Sound Practices Mailing List Files - Volume 1
=========================================================================
From: ecoleman@whidbey.net (Ed Coleman)
Subject: 7025,7025A ?
Date: Sat, 30 Aug 1997 19:13:45 -0800
Source: Sound Digest Archive v01.n007
Hey Folks, Can a 12ax7 be used as a substitute for a 7025 or 7025A ?Thanks Ed
Ed Coleman,M.ED.University of Washington.Transition Coordinator,Oak Harbor
School District,Oak Harbor Wa.USA.
Supporter of Habitat of Humanity and ZPG.Orbiting in the universe of
Marci,shining in the light of the dual sons Evan and Brendan Ameluxen
Coleman
Blackberries are all over the place! It's back to school!
=========================================================================
From: Scott Grammer <gesic@cdc.net>
Subject: Re: 7025,7025A ?
Date: Sat, 30 Aug 1997 23:43:20 -0400
Source: Sound Digest Archive v01.n007
Ed Coleman wrote:
> Hey Folks, Can a 12ax7 be used as a substitute for a 7025 or 7025A
> ?Thanks Ed
>
> Ed Coleman,M.ED.University of Washington.Transition Coordinator,Oak
> Harbor
> School District,Oak Harbor Wa.USA.
> Supporter of Habitat of Humanity and ZPG.Orbiting in the universe of
> Marci,shining in the light of the dual sons Evan and Brendan Ameluxen
> Coleman
> Blackberries are all over the place! It's back to school!
Yes, except it will be slightly noisier. The 7025 has a bifilar wound
filament intended to reduce hum induction from an ac filament supply.
Otherwise, it is a 12AX7.
S.G.
- --
"To save every cog and wheel is the first
precaution of intelligent tinkering." -Aldo Leopold.
Check out TubeDude's Webpage of Vacuum Tube Lore!
http://www.cdc.net/~gesic
=========================================================================
From: "JF" <jimfl@CyberRamp.net>
Subject: 7119, 5670, and 83 tubes
Date: Fri, 27 Nov 1998 15:51:22 -0600
Source: Sound Digest Archive v01.n506
Joes,
I'd like to pass on a source for these tubes at a great price. These tubes
are new.
5670W GE $1.00
7119 Amperex $5.50
83 Sylvania JAN $9.50
5842WA Raytheon $4.50
Price is in US dollars. Shipping is extra.
I just received a few myself. Lowell was a pleasure to deal with and
shipped the tubes promptly. Please contact him via e-mail at
k6kc@lightspeed.net
From Lowell's business card, I read that he also deals in old sound
equipment (1929 - 1975), theater and commercial, LPs, etc.
JF
=========================================================================
From: Grover Gardner <groverg@postoffice.att.net>
Subject: Re: 7119, 5670, and 83 tubes
Date: Fri, 27 Nov 1998 17:52:54 -0600
Source: Sound Digest Archive v01.n506
At 3:51 PM -0600 11/27/98, JF wrote:
>Joes,
>
>I'd like to pass on a source for these tubes at a great price. These tubes
>are new.
>
> 5670W GE $1.00
> 7119 Amperex $5.50
> 83 Sylvania JAN $9.50
> 5842WA Raytheon $4.50
>
>Price is in US dollars. Shipping is extra.
>
>I just received a few myself. Lowell was a pleasure to deal with and
>shipped the tubes promptly. Please contact him via e-mail at
>
> k6kc@lightspeed.net
>
>From Lowell's business card, I read that he also deals in old sound
>equipment (1929 - 1975), theater and commercial, LPs, etc.
>
>JF
A great tip, Jim--you could have kept this to yourself! ;-) Thanks for the
information.
Grover Gardner
groverg@postoffice.att.net
=========================================================================
From: "Mark Donen" <soledadd@worldnet.att.net>
Subject: 7189/el84
Date: Sun, 1 Feb 1998 19:34:29 -0500
Source: Sound Digest Archive v01.n178
Hi all,
I bought a Fisher X202 integrated real cheap for a friend this weekend. PP
7189 . It needs a couple of power tubes. A little checking around has made
me aware that 7189s are rather expensive. I know the tubes are not
identical but can the EL84/6BQ5 be substituted in this amp or are simple
mods needed?
TIA,
Mark
=========================================================================
From: "Aaron Bohnen" <bohnen@mail.unixg.ubc.ca>
Subject: Re: 7189/el84
Date: Mon, 2 Feb 1998 11:27:15 +0000
Source: Sound Digest Archive v01.n179
Hi everyone,
About the 7189/6BQ5/EL84 thing - there is only one new production tube
that I know of that can pass as a 7189 when used in an amp designed for
their higher plate voltage, and that is the Sovtek EL84M. The M
designates "military", or at least that's what I've been told. Many
people use these in place of 7189's. I don't have any myself and so
don't personally vouch for this but it certainly is worth
investigating.
On the flip side of the same coin, beware International Servicemaster
7189A's marked "W. Germany" as these are actually Sovtek 6BQ5's and
will glow cherry red in an amp designed for 7189's. This I can vouch
for since it happened to me just this weekend!
As I understand it, only the "M" Sovtek EL84's are suitable
substitutes. Maybe Ned at Triode Electronics, Steve at Angela Labs, or
Pat at STF Electronics would be able to confirm this.
best regards,
Aaron
> Check the plate voltage in the Fisher. EL84s are rated for 300V, 7189s
> are rated for 400V. I don't know if any of the current (Russian) EL84
> can be operated this much over ratings.
>
> GE Essential Characteristics:
>
> EL84/ 7189 7189 7189A
> 6BQ5 (pentode) (ultra-linear)
> ----------------------------------------------------------------------
> --- Vb max 300 400 375 440 volts Vsg
> max 300 300 375 400 volts Pd max 12.0 12.0 12.0 13.2 watts
> Psg max 2.0 2.0 2.0 2.2 watts
> ----------------------------------------------------------------------
> ---
>
> You are not the only one that is facing this problem. I need a couple
> of these things myself.
>
> --
> Dan Kerl
> dlkerl@ro.com
___________________________________________________________
Aaron Bohnen, B.A.Sc., E.I.T. email: bohnen@unixg.ubc.ca
- -Ph.D. Candidate, Civil Engineering Department, U.B.C.
- -Technicraft Engineering Services
=========================================================================
From: Grego Sanguinetti <grego@latticesemi.com>
Subject: Re: 7189/el84
Date: Mon, 2 Feb 1998 11:31:59 -0800 (PST)
Source: Sound Digest Archive v01.n179
On Mon, 2 Feb 1998, Dan Kerl wrote:
> Mark Donen wrote:
> > I bought a Fisher X202 integrated real cheap for a friend this weekend. PP
> > 7189 . It needs a couple of power tubes. A little checking around has made
> > me aware that 7189s are rather expensive. I know the tubes are not
> > identical but can the EL84/6BQ5 be substituted in this amp or are simple
> > mods needed?
>
> Check the plate voltage in the Fisher. EL84s are rated for 300V, 7189s are
> rated for 400V. I don't know if any of the current (Russian) EL84 can be
> operated this much over ratings.
Although I don't know about the X202, the Fisher X100 uses the 7189's and
definately takes advantage of the extra plate voltage. I would suspect the 202
does also. I have been told that one of the Sovtek variations, the EL84M I
think, is able to handle the extra voltage. I have not verified this myself.
- -grego
=========================================================================
From: Dan Kerl <dlkerl@ro.com>
Subject: Re: 7189/el84
Date: Mon, 02 Feb 1998 13:02:51 -0600
Source: Sound Digest Archive v01.n179
Mark Donen wrote:
>
> Hi all,
>
> I bought a Fisher X202 integrated real cheap for a friend this weekend. PP
> 7189 . It needs a couple of power tubes. A little checking around has made
> me aware that 7189s are rather expensive. I know the tubes are not
> identical but can the EL84/6BQ5 be substituted in this amp or are simple
> mods needed?
>
Check the plate voltage in the Fisher. EL84s are rated for 300V, 7189s are
rated for 400V. I don't know if any of the current (Russian) EL84 can be
operated this much over ratings.
GE Essential Characteristics:
EL84/ 7189 7189 7189A
6BQ5 (pentode) (ultra-linear)
- -------------------------------------------------------------------------
Vb max 300 400 375 440 volts
Vsg max 300 300 375 400 volts
Pd max 12.0 12.0 12.0 13.2 watts
Psg max 2.0 2.0 2.0 2.2 watts
- -------------------------------------------------------------------------
You are not the only one that is facing this problem. I need a couple of
these things myself.
- --
Dan Kerl
dlkerl@ro.com
=========================================================================
From: evaguido <EvaGuido@iaehv.nl>
Subject: Re: 7189/el84
Date: Mon, 02 Feb 1998 20:17:56 +0100
Source: Sound Digest Archive v01.n179
Hi
Go for the sovteks (the military ones, I am sorry I hate the army) or the
Golden Dragons. Not too expensive though ?
the original Philips sound like heaven, but these are expensive
Guido
At 19:34 1-2-98 -0500, Mark Donen wrote:
>Hi all,
>
>I bought a Fisher X202 integrated real cheap for a friend this weekend. PP
>7189 . It needs a couple of power tubes. A little checking around has made
>me aware that 7189s are rather expensive. I know the tubes are not
>identical but can the EL84/6BQ5 be substituted in this amp or are simple
>mods needed?
>
>TIA,
>
>Mark
>
>
=========================================================================
From: RICHARD JONES <RJ0101@Sprynet.Com>
Subject: 71A and preamp tubes
Date: Wed, 14 Oct 1998 12:49:01 -0500
Source: Sound Digest Archive v01.n454
At the moment I have a 76 based pre-amp. I am thinking of building a
pre-amp with plate loading chokes.
I am looking at many tubes including 71A, 46, 5687, 12AU7, 7119, 7044, 5842.
Probably i will put a Magnequest parafeed tranny on the output.
Any recommendations?
Also would it just be easier to build a integrated amp instead? Anyone
tried the 6AS7 in a parafeed or regular SE design?
Thanks for any help.
Richard.
=========================================================================
From: David Home <DHome@creo.com>
Subject: RE: 71A and preamp tubes
Date: Wed, 14 Oct 1998 15:10:49 -0700
Source: Sound Digest Archive v01.n454
What voltage can the C4S take across it?
-----Original Message-----
From: tubesguy@mail.execpc.com
[mailto:tubesguy@mail.execpc.com]
Sent: Wednesday, October 14, 1998 2:29 PM
To: RICHARD JONES
Cc: sound@deliverator.io.com
Subject: Re: 71A and preamp tubes
>At the moment I have a 76 based pre-amp. I am thinking of
building a
>pre-amp with plate loading chokes.
>
>I am looking at many tubes including 71A, 46, 5687, 12AU7,
7119, 7044, 5842.
>
>Probably i will put a Magnequest parafeed tranny on the
output.
>
>Any recommendations?
>Richard.
Yup. First try a C4S load on the 76, substituted for the
plate resistor
that is there now. If you like that, then think about using
the 15k nickel
parafeed B7 output tranny. That should be enough. If not,
then start
screwing around with other, perhaps less linear, tubes. HTH
- - Pat
Pat Currie (tubesguy@execpc.com)
=========================================================================
From: tubesguy@mail.execpc.com (Patrick Currie)
Subject: Re: 71A and preamp tubes
Date: Wed, 14 Oct 1998 16:28:49 -0500
Source: Sound Digest Archive v01.n454
>At the moment I have a 76 based pre-amp. I am thinking of building a
>pre-amp with plate loading chokes.
>
>I am looking at many tubes including 71A, 46, 5687, 12AU7, 7119, 7044, 5842.
>
>Probably i will put a Magnequest parafeed tranny on the output.
>
>Any recommendations?
>Richard.
Yup. First try a C4S load on the 76, substituted for the plate resistor
that is there now. If you like that, then think about using the 15k nickel
parafeed B7 output tranny. That should be enough. If not, then start
screwing around with other, perhaps less linear, tubes. HTH - Pat
Pat Currie (tubesguy@execpc.com)
=========================================================================
From: Grego Sanguinetti <grego@lscpdx.latticesemi.com>
Subject: Re: 71A and preamp tubes
Date: Fri, 16 Oct 1998 15:43:35 -0700
Source: Sound Digest Archive v01.n457
On Wed, Oct 14, 1998 at 12:49:01PM -0500, RICHARD JONES wrote:
> At the moment I have a 76 based pre-amp. I am thinking of building a
> pre-amp with plate loading chokes.
>
> I am looking at many tubes including 71A, 46, 5687, 12AU7, 7119, 7044, 5842.
>
> Probably i will put a Magnequest parafeed tranny on the output.
>
> Any recommendations?
Yes!
first off, I really like Pat's idea, worth trying I think.
quite a wide variety of tubes to choose from, not alot in common!
A wide variety of plate impedances makes me question the logic
of comparing all these with the same output tranny.
Drop the 12AU7 from the list.
The 5842 is fine but you have some better options listed.
The 71A, and 46 are kind of in their own category here. PSRR is low
on the these given the directly heated construction so that might be
a concern. Sweet sounding tubes though. My personal preferance for
preamps would be the 71A, a very revealing tube. Both of these will
probably need a voltage gain stage ahead of them though. The design
will look like a little power amp. With the right secondaries, it
would make a nice headphone amp.
The 5687/7119/7044 is a great tube, very versatile tube. Good sound,
Fairly low Rp wide band, low distortion... not much in the gain
department but hanging in there with the rest of this crowd, except
the 5842. Hard to go wrong with this one.
> Also would it just be easier to build a integrated amp instead?
maybe, but not as much fun.
> Anyone tried the 6AS7 in a parafeed or regular SE design?
not me.
- -grego
=========================================================================
From: ldmoore@lucent.com
Subject: 71A Data
Date: 29 Aug 97 07:25:00 -0400
Source: Sound Digest Archive v01.n004
Does anyone know the maximum plate dissipation for the 71A? Also, does
anyone have characteristic curves?
TIA,
L.D. Moore
ldmo@lucent.com
=========================================================================
From: Martin Needleman <mrndlmn@bayserve.net>
Subject: Re: 71A Data
Date: Fri, 29 Aug 1997 11:12:42 -0700
Source: Sound Digest Archive v01.n005
ldmoore@lucent.com wrote:
>
> Does anyone know the maximum plate dissipation for the 71A? Also, does
> anyone have characteristic curves?
>
> TIA,
> L.D. Moore
> ldmo@lucent.com
According to my old RCA Receiving Tube Manual it's 3.6 watts (180 volts
maximum at 20 mA)
=========================================================================
From: "Larry D. Moore" <l-moore@onu.edu>
Subject: 71A plate dissipation
Date: Tue, 05 Jan 1999 18:13:12 -0500
Source: Sound Digest Archive v01.n559
Well, I've looked everywhere...I know I asked this question before and jc
answered it; but, I can't find the email and I can seeem to "easily" find
it in the achives, so please help.
TIA,
L.D. Moore
p.s. I promise to write it in my tube manual.
=========================================================================
From: "Daniel J. Marshall" <danmarshall@worldnet.att.net>
Subject: 7355 specs, etc.
Date: Wed, 11 Mar 1998 21:16:15 -0800
Source: Sound Digest Archive v01.n214
Hi all,
I hate to trouble you all with this mundane stuff, but none of the half
dozen tube manuals I have lists the 7355 output tube and I have not used
them before. So, I would appreciate the specs if someone has them
handy. Better still, the PP load impedance at which they are
customarily operated. Yeah, I know, I could measure the turns ratio and
finger it out, but I have been pretty busy lately, so prefer to take the
easy way out.
I came across a Harmon Kardon Award Series A500 amplifier a while ago
that uses 7355s. On the plus side it has two Telefunken 12AX7s that
test at 100% plus and a Mullard Master 12AX7 at nearly a hundred percent
and the output tubes are still quite good. On the down side, the
chassis is filthy and has a fair bit of rust, though the faceplate is
not too bad. Unfortunately, the tone control circuits have a wad of
ceramic capacitors that would need to be changed. All in all, it is not
my bag, as I am currently thinking along the lines of minimal circuitry,
so I feel inclined to scavenge its output transformers and 12AX7s and
sell the output tubes to someone who needs them. This thing could be
restored, but would never be a thing of beauty without an inordinate
amount of work and I am not confident that it would be worth it.
I have some 6B4s I would like to build into a PP amp and need some
suitable output trannies. I suspect these are a bit on the high side,
impedancewise. Is there anything wrong with exceeding the rated plate
voltage of 6B4s to get a better match with a higher-than-optimum
impedance output transformer? I am not asking whether this is
theoretically possible, rather, practically speaking, would it likely
cause reliability problems with 6B4s. Will they arc over, or suffer
harm from operating at a plate voltage exceeding their rated maximum?
The book say 5,000 ohms PP for cathode bias and 3,000 for fixed bias.
Anything wrong with maybe upping the secondary tap to the next impedance
to halve the primary impedance? I would prefer to operate fixed bias, I
think. Anyway, if anyone has experience along this line, I would
appreciate hearing about the details. Thanks.
Dan Marshall.
=========================================================================
From: An-shyang Chu <achu@sandia.gov>
Subject: Re: 7355 specs, etc.
Date: 12 Mar 1998 08:02:28 -0700
Source: Sound Digest Archive v01.n214
Hi Dan,
Here is what I find in GE Essential Characteristics (reprited by Antique
Electronic Supply):
7355 beam power amplifier
filament: 6.3 @ 0.8 A
max plate diss: 18 watts
max plate volts: 500V
max screen volts and diss: 500V, 3.5 watts
class A: 250V plate @ 62 mA, 225V screen @ 3.2 mA, bias 15V, rp~ 42000 ohm, Gm ~
7600 and load line @ 2500 ohm with 9 watts out.
class AB: (1) 400V plate @ 56 mA, 300V screen @ 3.5 mA, bias @ 34 V, load line @
5000 ohm (p-p) with out put of 40 watts or (2) 300V plate @ 100 mA, screen 250V
@ 5.5 mA, bias @ 21V and load line of 4000 ohm (p-p) @ 28.5 watts out.
There is no sapacitance listed, sorry.
hopper
_______________________________________________________________________________
Subject: 7355 specs, etc.
From: danmarshall@worldnet.att.net at hubsmtp
Date: 3/11/98 10:43 PM
Hi all,
I hate to trouble you all with this mundane stuff, but none of the half
dozen tube manuals I have lists the 7355 output tube and I have not used
them before. So, I would appreciate the specs if someone has them
handy. Better still, the PP load impedance at which they are
customarily operated. Yeah, I know, I could measure the turns ratio and
finger it out, but I have been pretty busy lately, so prefer to take the
easy way out.
I came across a Harmon Kardon Award Series A500 amplifier a while ago
that uses 7355s. On the plus side it has two Telefunken 12AX7s that
test at 100% plus and a Mullard Master 12AX7 at nearly a hundred percent
and the output tubes are still quite good. On the down side, the
chassis is filthy and has a fair bit of rust, though the faceplate is
not too bad. Unfortunately, the tone control circuits have a wad of
ceramic capacitors that would need to be changed. All in all, it is not
my bag, as I am currently thinking along the lines of minimal circuitry,
so I feel inclined to scavenge its output transformers and 12AX7s and
sell the output tubes to someone who needs them. This thing could be
restored, but would never be a thing of beauty without an inordinate
amount of work and I am not confident that it would be worth it.
I have some 6B4s I would like to build into a PP amp and need some
suitable output trannies. I suspect these are a bit on the high side,
impedancewise. Is there anything wrong with exceeding the rated plate
voltage of 6B4s to get a better match with a higher-than-optimum
impedance output transformer? I am not asking whether this is
theoretically possible, rather, practically speaking, would it likely
cause reliability problems with 6B4s. Will they arc over, or suffer
harm from operating at a plate voltage exceeding their rated maximum?
The book say 5,000 ohms PP for cathode bias and 3,000 for fixed bias.
Anything wrong with maybe upping the secondary tap to the next impedance
to halve the primary impedance? I would prefer to operate fixed bias, I
think. Anyway, if anyone has experience along this line, I would
appreciate hearing about the details. Thanks.
Dan Marshall.
=========================================================================
From: Ron Bales <rbales@gte.net>
Subject: Re: 7355 specs, etc.
Date: Thu, 12 Mar 1998 08:40:18 -0500
Source: Sound Digest Archive v01.n214
Daniel J. Marshall wrote:
>
> Hi all,
>
> I hate to trouble you all with this mundane stuff, but none of the half
> dozen tube manuals I have lists the 7355 output tube and I have not used
> them before. So, I would appreciate the specs if someone has them
> handy. Better still, the PP load impedance at which they are
> customarily operated. Yeah, I know, I could measure the turns ratio and
> finger it out, but I have been pretty busy lately, so prefer to take the
> easy way out.
Hi Dan, my GE Essentials lists for the 7355
Class AB1 Amplifier
plate V ScreenV Grid-V PlatemV ScreenmV Load PP Rated power
400 300 34 56 3.5 5,000 40
300 250 21 100 5.5 4,000 28.5
> I have some 6B4s I would like to build into a PP amp and need some
> suitable output trannies. I suspect these are a bit on the high side,
> impedancewise.
It looks to me that your 6B4G's will be happy with anything in that
range. My 6A3's are not at all unhappy running into a pair of 5.3K
output I stole from a Pilot receiver that didn't have 7591s.
ROn
=========================================================================
From: Grover Gardner <groverg@postoffice.att.net>
Subject: Re: 7355 specs, etc.
Date: Thu, 12 Mar 1998 08:52:44 -0600
Source: Sound Digest Archive v01.n214
At 9:16 PM -0800 3/11/98, Daniel J. Marshall wrote:
>Hi all,
>
>I hate to trouble you all with this mundane stuff, but none of the half
>dozen tube manuals I have lists the 7355 output tube and I have not used
>them before. So, I would appreciate the specs if someone has them
>handy. Better still, the PP load impedance at which they are
>customarily operated. Yeah, I know, I could measure the turns ratio and
>finger it out, but I have been pretty busy lately, so prefer to take the
>easy way out.
Hey Dan--the 7355 calls for 4K p-p at 300 volts for 28 watts Po, or 5K p-p
at 400 volts for 40 watts Po. I suspect the former with the Hk but maybe
you can check the voltages and see where they're running it. Either way
there's no reason you couldn't use these trannies for 6B4s--I've used Dyna
trannies at 4.3K with 6B4s in class AB and the lower load is pretty perky
sounding! OTOH, you could rebuild the existing circuit on a fresh
chassis--the old HK amps are pretty sweet-sounding. Either way I'm sure
you could put those nice lil trannies to good use :-)
=========================================================================
From: evaguido <EvaGuido@iaehv.nl>
Subject: Re: 7355 specs, etc.
Date: Thu, 12 Mar 1998 19:52:27 +0100
Source: Sound Digest Archive v01.n215
>> I have some 6B4s I would like to build into a PP amp and need some
>> suitable output trannies. I suspect these are a bit on the high side,
>> impedancewise.
2.5 k to 3.5 k will be fine for each 2A3, 6A3 or 6B4G
Guido
>It looks to me that your 6B4G's will be happy with anything in that
>range. My 6A3's are not at all unhappy running into a pair of 5.3K
>output I stole from a Pilot receiver that didn't have 7591s.
>
>ROn
>
>
>
=========================================================================
From: Paul Joppa <pdj@ISDNseattle.net>
Subject: Re: 7355 specs, etc.
Date: Thu, 12 Mar 1998 22:45:09 -0800
Source: Sound Digest Archive v01.n215
GE 14th ed. says, 40w @ 5000CT @ 400/300v; 28w @4000CT @ 300/250v.
Should be fine with 6B4s at the usual 300v/50mA. Possibly a suitable
power transformer even.
- -Paul Joppa
Daniel J. Marshall wrote:
>
> Hi all,
>
> I hate to trouble you all with this mundane stuff, but none of the half
> dozen tube manuals I have lists the 7355 output tube and I have not used
> them before. So, I would appreciate the specs if someone has them
> handy. Better still, the PP load impedance at which they are
> customarily operated. Yeah, I know, I could measure the turns ratio and
> finger it out, but I have been pretty busy lately, so prefer to take the
> easy way out.
>
> I came across a Harmon Kardon Award Series A500 amplifier a while ago
> that uses 7355s. On the plus side it has two Telefunken 12AX7s that
> test at 100% plus and a Mullard Master 12AX7 at nearly a hundred percent
> and the output tubes are still quite good. On the down side, the
> chassis is filthy and has a fair bit of rust, though the faceplate is
> not too bad. Unfortunately, the tone control circuits have a wad of
> ceramic capacitors that would need to be changed. All in all, it is not
> my bag, as I am currently thinking along the lines of minimal circuitry,
> so I feel inclined to scavenge its output transformers and 12AX7s and
> sell the output tubes to someone who needs them. This thing could be
> restored, but would never be a thing of beauty without an inordinate
> amount of work and I am not confident that it would be worth it.
>
> I have some 6B4s I would like to build into a PP amp and need some
> suitable output trannies. I suspect these are a bit on the high side,
> impedancewise. Is there anything wrong with exceeding the rated plate
> voltage of 6B4s to get a better match with a higher-than-optimum
> impedance output transformer? I am not asking whether this is
> theoretically possible, rather, practically speaking, would it likely
> cause reliability problems with 6B4s. Will they arc over, or suffer
> harm from operating at a plate voltage exceeding their rated maximum?
> The book say 5,000 ohms PP for cathode bias and 3,000 for fixed bias.
> Anything wrong with maybe upping the secondary tap to the next impedance
> to halve the primary impedance? I would prefer to operate fixed bias, I
> think. Anyway, if anyone has experience along this line, I would
> appreciate hearing about the details. Thanks.
>
> Dan Marshall.
=========================================================================
From: Steve Fellini <steve@helix.nih.gov>
Subject: 755Cs [ was: antique stuffs ]
Date: Wed, 15 Jul 1998 18:24:56 -0400 (EDT)
Source: Sound Digest Archive v01.n344
From: Acrosound@aol.com
Date: Wed, 15 Jul 1998 16:28:50 EDT
Hey Mike...
Has anyone listened to the 755C's....I have at least two pair of these...any
impressions or comments from anyone on the C's???
Yeah, I've been listening to 755Cs on open baffles (roughly 3' x 3').
These are great speakers in the midrange. Wonderful vocals. Best for
small scale music... no surprise.
For the music I listen to, they are fully the equal of
Lowther/Medallions (not as nice on top, but smoother sounding mids and
no worse lower down). And far less money.
I've "heard" that the 755As work better in cabinets while the 755Cs
work better in open baffles. Haven't heard As (yet), but I had the Cs
in cabs and didn't fall in love with them there.
Steve
Steve.Fellini@nih.gov
=========================================================================
From: Ron Bales <rbales@gte.net>
Subject: 755 incognito
Date: Fri, 09 Jan 1998 22:05:26 -0500
Source: Sound Digest Archive v01.n157
found a University Sound PA column in a second hand shop. Took it apart
to find four 8" speakers two each of two different types. One pair has
a black plastic dome shaped dust cover and is not that interesting. The
other pair have fairly flat stamped steel frames in some sort of dull
silver finish. The cone is the interesting part the surround is red,
pleated and flat, about 5/8" wide. The cone proper is black paper and
conventional with a whizzer cone around the dust cap. the Whizzer has a
series of 1/8" holes near its perimeter.
Is this some variant on the 755C formula? I'm agoing to experiment with
these a bit. Might be another answer to low cost full range drivers.
The only apparent difference between these two pair of drivers is the
cone and dust cap, looks like a passive two way deal.
If anyone has specs for drivers numbered UNIVERSITY 5003022941 and OAK-
8 74, I'd really appreciate it. I'll post any interesting results.
ROn
=========================================================================
From: Josh Karnes <karnes@usa.net>
Subject: 7591A --> 6550 conversion
Date: Thu, 16 Oct 1997 09:46:11 -0500
Source: Sound Digest Archive v01.n071
the experts agree, it is highly unlikely that svetlana will make any
7591A's for general consumption anytime until the NEXT MILLENIUM!!
since i have this very nice quartet of nearly-NOS tung-sol 6550's sitting
here and their amps awaiting some repair, and i'm considering switching my
fisher to some other tube (5881's presumably), i was wondering whether the
6550 is a better match or will even work in place of the 7591A?
there is some socket rewiring and a handful of other little trickies to
make the 5881 switch, one of which is adjustment of the feedback (which i
am almost convinced needs to be handled by a dual-ganged pot for
adjustability). still you lose half or more of the original power output,
wondering what the ramifications of using a 6550 in there might be.
trying to make this as reversible a mod as possible while still giving me
the opportunity to use some new tubes.
later-
- -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
josh_karnes:
shileen's husband, jordan and hannah's daddy, guitarist, drummer,
composer, songwriter, audiophile, computer geek, mechanic, carpenter,
wannabe gourmet chef, keeper of the faith <><
=========================================================================
From: match@ee.utah.edu
Subject: Re: 7591A --> 6550 conversion
Date: Thu, 16 Oct 1997 14:14:35 +0000
Source: Sound Digest Archive v01.n071
> since i have this very nice quartet of nearly-NOS tung-sol 6550's sitting
> here and their amps awaiting some repair, and i'm considering switching my
> fisher to some other tube (5881's presumably), i was wondering whether the
> 6550 is a better match or will even work in place of the 7591A?
No way, Josh. The heater current is 1.6 amps for each of the 6550's
whereas it's only .8 amps for the 7591's. You would need to coax an
additional 3.2 amps of filament current from the power transformer!
My vote would be for 6L6GB's or maybe something similar.
Marvin
=========================================================================
From: Scott Grammer <gesic@cdc.net>
Subject: Re: 7591A --> 6550 conversion
Date: Thu, 16 Oct 1997 21:04:42 -0400
Source: Sound Digest Archive v01.n071
http://www.triodeel.com/7591.htm
This is a page from Teiode Electronics website that I think might solve
the problem.
Cheers!
S.G.
- --
"To save every cog and wheel is the first
precaution of intelligent tinkering." -Aldo Leopold.
Check out TubeDude's Webpage of Vacuum Tube Lore!
http://www.cdc.net/~gesic
=========================================================================
From: davidbarnett@aristotle.net (David N. Barnett)
Subject: Re: 7591A --> 6550 conversion
Date: Thu, 16 Oct 1997 22:12:46 GMT
Source: Sound Digest Archive v01.n071
On Thu, 16 Oct 1997 14:14:35 +0000, match@ee.utah.edu wrote:
>No way, Josh. The heater current is 1.6 amps for each of the 6550's
>whereas it's only .8 amps for the 7591's. You would need to coax an
>additional 3.2 amps of filament current from the power transformer!
Not only that, but the 6550 doesn't have as much gain, requiring more
voltage from the drivers. And along with that, it takes a lot of B-
voltage to pull the 6550 grids down for AB1 operation; probably
outside the range of adjustment of any 7591 amp.
- --dnb
=========================================================================
From: match@ee.utah.edu
Subject: Re: 7591A --> 6550 conversion
Date: Fri, 17 Oct 1997 09:57:16 +0000
Source: Sound Digest Archive v01.n072
David wrote:
> On Thu, 16 Oct 1997 14:14:35 +0000, match@ee.utah.edu wrote:
>
> >No way, Josh. The heater current is 1.6 amps for each of the 6550's
> >whereas it's only .8 amps for the 7591's. You would need to coax an
> >additional 3.2 amps of filament current from the power transformer!
>
> Not only that, but the 6550 doesn't have as much gain, requiring more
> voltage from the drivers. And along with that, it takes a lot of B-
> voltage to pull the 6550 grids down for AB1 operation; probably
> outside the range of adjustment of any 7591 amp.
>
> --dnb
>
Actually the 6L6 and variants don't have near the gain either, but at
least you can get close on the bias. I'm not sure of a better
replacement, perhaps one exists, but a 6L6 will work.
Marvin
=========================================================================
From: Jeremy Epstein <70664.154@CompuServe.COM>
Subject: 7591 puzzler
Date: Wed, 15 Oct 1997 15:40:55 -0400
Source: Sound Digest Archive v01.n070
Joenetters:
A list member and I have tried to consummate a deal for a pair of
7591's and we have run into a snag. NOTE: we are having no trouble
resolving the deal amicably, this is _not_ a call for a referee.
However, we both would like to know what the heck is going on.
Intellectual curiousity and all that. I asked Ned Carlson, of Triode
Electronics, a Chicago tube dealer and Ampeg guru, what was going on
and his reply is included below.
The equipment I have is an Ampeg Rocket R-12A guitar combo amp, which
uses the circuit diagrammed at :
http://users.aol.com/portaflex/schems/r-12a.gif
for the handy reference of all you Joenetters.
I have a pair of Ampeg-labelled Sylvania 7591A's in it, presumably
these have been in there since the amp was built in the early 60's.
It works fine and was serviced about a year ago by a competent tech.
When the "new" tubes arrived (Lowery Organ-labelled 7591's) I
installed them in the amp. With either one of the old tubes in, and
either one of the new tubes installed, OR with both the new tubes
installed, there an extremely loud hum comes from the amp,
independent of the volume knob's setting, and I'm pretty sure no signal
can be heard. (I turned the amp off immediately each time for fear of
damaging the speaker - this hum was that loud - so I'm not really
sure about whether the signal is getting through at all underneath
the hum.)
One person I asked suggested that I had turned the tube and installed
it aligned to the wrong pins - so I was careful not to do that when I
checked again, and the problem still persisted. The alignment keys
are intact anyway so doing this would have been unlikely to begin with.
Here is my correspondence with Ned :
NED> From: Ned Carlson > INTERNET:triodeel@ameritech.net
NED> Subj: Re: 7591/A difference? HELP!
<snip>
J > >Are the new pair de facto bad, or are the 7591's different by some fatal
J > >way from the "a"'s? Or - is there some kind of "manufacturers option"
J > >problem, mis- or un-connected pin, that I need to know about.
NED> What you have is a heater-cathode short or leakage
NED> In a fixed-bias amplifier you might not notice as the heater
NED> CT is connected to ground (literally connected right to the cathode).
NED> You could try hooking the heater CT to cathodes
NED> (top of the 140 cathode resistor), see if the hum goes away.
J > >I don't want to send these back if they are working as they are supposed
J > >to, that's not HIS fault, but if they are bad I will, of course.
NED> Naw, hum isn't normal. Note that certain tube testers won't
NED> check high-resistance (ie: enough to make it hum) shorts
NED> too well, or they might have worked fine in a different amp..
NED> so he might not have known, but from your point of view, they're NG.
Now, the seller (I'm leaving him anonymous although he can certainly
jump in here if he wants to, I'm leaving it up to him, and I've
edited out references to his gear so he might remain anonymous more
easily if he wants to do that) had checked the tubes before the sale,
and they tested very good. Here is what he did when he got them back :
SEL> Jeremy,
SEL>
SEL> I got the tubes back in the mail last night. I plugged them back into
SEL> the tube tester, and still got no shorts on either one. So I then
SEL> measured the resistance between pins on both tubes, and compared them to
SEL> the tired old tubes I got with the (HIFI). The heater pins showed no
SEL> shorts of any kind, and I tried to measure a resistance between the
SEL> heater and all of the other pins on both tubes, using my multimeter.
SEL> There was no leakage whatsoever, even on the 2000 megaohm (yup, my
SEL> multimeter measures that high, and can even get a resistance from a
SEL> pencil trace.) Nothing. It read open line on all pins other than the
SEL> other heater pin, which at that scale read as a short.
SEL>
SEL> I also popped them into the (HIFI) and listened to them. I even tried to
SEL> unbalace the hum pot to see if that would do something, but the hum was
SEL> no worse than the other tubes I got with the (HIFI) unit under any
SEL> circumstances.
Also, from another post:
SEL> BTW, I tested the resistance between the pins
SEL> with the tube cold, and also with the tube quite hot. After running them
SEL> in the (HIFI) for about an hour under normal listening conditions, they
SEL> were quite hot, and I pulled them out (carefully) and measured the
SEL> inter-pin resistances.
Continuing :
SEL> The problem might still be in your amp. I was curious, and found the
SEL> following post in my archived copies of the joenet posts that I'm
SEL> attaching describing a simular problem.
<snipped a post describing Josh Karnes' trials and tribulations : it's
probably not the same problem IMHO, he's talking small signal tubes, and
he can hear signal under the hum and I _think_ I can't.>
Both Mr. Seller and myself want to know the following : is there
something wrong with my amp? Is there something wrong with BOTH
tubes? Is there some gremlin like a manufacturer's option, dead pin,
missing optional connection, blah blah blah, bedeviling us? Is there
some key difference between 7591 and 7591A that is turning up here?
Does anybody care to offer any suggestions for things we can try to
help us learn more about this mystery?
I also want to put in a plug for Ned here : he's been a big help in
this and other situations and is from all I can tell a nice guy. Buy
tubes from him if you get a chance.
- -j
=========================================================================
From: "Bottlehead" <Bottlehead@prodigy.net>
Subject: Re: 7591 puzzler
Date: Wed, 15 Oct 1997 16:38:40 -0700
Source: Sound Digest Archive v01.n070
>
> Or could it be that organs and guitars don't like to mix? :-).
>
You kiddin'?
How about Wes Montgomery and Jimmy Smith, or Danny Gatton and Joey de
Francesco?
Doc B.
=========================================================================
From: "Markowitz, Gary" <MarkowitzG@nabisco.com>
Subject: RE: 7591 puzzler
Date: Wed, 15 Oct 1997 17:49:50 -0400
Source: Sound Digest Archive v01.n070
Jeremy and all,
Thanks for the offer to keep my identity secret, but there's really no
need. We both just want to figure out what's going on.
To fill in the blanks, The tube tester I used was an Hikock 532, on
which I've tested other octal tubes before. The (HIF) was the Eico
ST-70 I picked up last weekend.
I checked the URL that Jeremy posted against the data sheets of the
7591, and the pinouts look identical.
Or could it be that organs and guitars don't like to mix? :-).
Thanks in advance for any help you might have unraveling this mystery.
Gary Markowitz
MarkowitzG@nabisco.com
- ------------------------------------------------------------------------
- ----------------------------
"Into the keyboard, thru the processor, off the NIC, past the gateway,
nothing but Net"
=========================================================================
From: Josh Karnes <karnes@usa.net>
Subject: Re: 7591 puzzler
Date: Thu, 16 Oct 1997 08:32:44 -0500
Source: Sound Digest Archive v01.n070
>I have a pair of Ampeg-labelled Sylvania 7591A's in it, presumably
>these have been in there since the amp was built in the early 60's.
>It works fine and was serviced about a year ago by a competent tech.
>
>When the "new" tubes arrived (Lowery Organ-labelled 7591's) I
>installed them in the amp. With either one of the old tubes in, and
>either one of the new tubes installed, OR with both the new tubes
>installed, there an extremely loud hum comes from the amp
>SEL> The problem might still be in your amp. I was curious, and found the
>SEL> following post in my archived copies of the joenet posts that I'm
>SEL> attaching describing a simular problem.
>
><snipped a post describing Josh Karnes' trials and tribulations : it's
>probably not the same problem IMHO, he's talking small signal tubes, and
>he can hear signal under the hum and I _think_ I can't.>
ok, well my problem that was probably pointed out here seems to have been a
turntable grounding problem, that is if it is the RECENT hum problem. this
might be a reference to a very old problem with some 6550 amps which
resulted from a bad filter cap, but unlikely applicable either way, imho.
>Both Mr. Seller and myself want to know the following : is there
>something wrong with my amp? Is there something wrong with BOTH
>tubes? Is there some gremlin like a manufacturer's option, dead pin,
>missing optional connection, blah blah blah, bedeviling us? Is there
>some key difference between 7591 and 7591A that is turning up here?
i don't think there is really any difference between 7591 and 7591A,
functionally at least. darn it if i don't have the tube databook handy.
one of you guys has this online, don't you? could you forward me the URL
and i'll look into it more seriously.
the circuit looks pretty normal to me! can't see what the problem could
have been. of course there are some "optionally" connected pins in the
7591 i think, you might want to double check. there are some connections
which are connected to two pins (might just be the screen grid... i NEED
that databook!). it would be worthwhile to jumper the socket to make these
connections just in case. maybe mr. seller (who seems to have been
identified by now) might be kind enough to crack open the eico and see
exactly how the socket is connected so you can duplicate that in the ampeg.
>
>Does anybody care to offer any suggestions for things we can try to
>help us learn more about this mystery?
the only thing i can think is that perhaps there is an unconnected pin that
just happens to be connected in the eico. first place i'd look is in the
wiring of the socket that it works in, which is the eico. anyone have a
schematic for an eico st-70 in a scanned format that we can look at on the
net? this would be intensely handy anyway for me since a friend is likely
to buy one soon and i imagine i will get "tech" duties when it arrives.
i am intensely interested. i will look at my fisher tonight (the
schematic) to see how the sockets are connected just to add that info into
the pot.
later-
- -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
josh_karnes:
shileen's husband, jordan and hannah's daddy, guitarist, drummer,
composer, songwriter, audiophile, computer geek, mechanic, carpenter,
wannabe gourmet chef, keeper of the faith <><
=========================================================================
From: Josh Karnes <karnes@usa.net>
Subject: Re: 7591 puzzler
Date: Thu, 16 Oct 1997 09:26:12 -0500
Source: Sound Digest Archive v01.n070
ok i found the 7591A data on line, still don't know what is different about
it and the regular old 7591. looks like the only pins which have two
connected to the same part are the screen grids, which according to the
schematic posted for the ampeg are both connected so there should be no
problem assuming the wiring in the amp actually matches the schematic.
i still would check the sockets for wiring though!
later-
- -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
josh_karnes:
shileen's husband, jordan and hannah's daddy, guitarist, drummer,
composer, songwriter, audiophile, computer geek, mechanic, carpenter,
wannabe gourmet chef, keeper of the faith <><
=========================================================================
From: "Markowitz, Gary" <MarkowitzG@nabisco.com>
Subject: RE: 7591 puzzler
Date: Thu, 16 Oct 1997 09:35:30 -0400
Source: Sound Digest Archive v01.n070
Doc,
>You kiddin'?
>How about Wes Montgomery and Jimmy Smith, or Danny Gatton and
>Joey de Francesco?
Were talkin' parts here. Not musicians! :-).
Gary Markowitz
MarkowitzG@nabisco.com
- ------------------------------------------------------------------------
- ----------------------------
"Into the keyboard, thru the processor, off the NIC, past the gateway,
nothing but Net"
=========================================================================
From: Joe Pledger <doodle@navicom.com>
Subject: Re: 7591 puzzler
Date: Thu, 16 Oct 1997 09:35:26 -0700
Source: Sound Digest Archive v01.n071
Josh Karnes wrote:
-snip-
> i don't think there is really any difference between 7591 and 7591A,
> functionally at least. darn it if i don't have the tube databook handy.
> one of you guys has this online, don't you? could you forward me the URL
> and i'll look into it more seriously.
>
-snip-
This won't be much help, but here's what my GE book shows:
7591 & 7591-A are listed with identical characteristics (to the extent
that the manual covers) . Since I don't have a graphics tablet input
to e-mail msg screen, I'll try to describe the pin desig's.
starting with heater and going toward plate: (fil, cathode, three
grids, plate)
Heater: Pins 2 & 7
cathode: Pin 5
1st grid: pin 6
2nd grid: pins 8 & 4
3rd grid: pin 5 (internal connection to cathode)
plate: pin 3
(pin 1 shows no connection.
Sounds like the answer must be in the circuit differences between the
two amps.
Regards,
Joe Pledger
=========================================================================
From: Robert Root <rrjlife@earthlink.net>
Subject: 7788 as driver:
Date: Sun, 09 Aug 1998 21:28:12 -0700
Source: Sound Digest Archive v01.n382
One of my friends has reworked his 300B amp. He has been using
the Tango NY-15 Ni for some time and finds it more detailed than
past units. I sent him some 6CJ3's and with his LCLC network is more
detailed with better bass. He is using We-300B's at 410volta/60ma.
He has tried various drivers, but changed to the 437A. He is using
Tads with 416-8B in Onken for the bass. He likes the 437, but tried
his trusty 7788-triode connected and is really elated with the
results. The 7788 is cap coupled to the 300B by an AN 0.22 copper/oil
He runs the 7788 at 210volts/7ma and claims high output and good
sensitivity with this setup. Could this really be?
=========================================================================
From: Grego Sanguinetti <grego@lscpdx.latticesemi.com>
Subject: Re: 7788 as driver:
Date: Mon, 10 Aug 1998 10:50:12 -0700
Source: Sound Digest Archive v01.n383
On Mon, Aug 10, 1998 at 11:40:40PM +0700, Johari Yip wrote:
> Hi guys,
>
> Robert, you must have read my mind. I'm also contemplating on using the 7788
> as driver for my SE 845 running low and hot. 450V at 80mA is what the 845 is
> going to have. I would like to know whether the 7788, triode connected, will
> be a good driver for this particular task? Appreciate your views.
Not directed to me, but I will butt in anyway.
Yes, I have used 845s in the B52 amp. There the 7788 is going through
a 1:2 IT.
The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
However it does not require lots of current to sound nice, as indicated
by Robert's friend's operating point.
Which leads me to a note about the 7788 driver in the SP15 article. There
is a mistake on the schematic. The schematic shows the model number for the
modified 2K IT, however the indicated current for the driver is for the
stock 5K IT. With the 2K IT the driver runs close to 50mA for some 7788's.
When running with the 2K IT, I swapped the lower 0C3 for an 0A3 (wild looking)
to reduce the Vp to about 180v. That drops the current to about 17mA.
Sounds fine that way.
The measured distortion with this driver (which is VERY low!) varies little
with current and operating point, compared with other such tubes I have
checked out. Kind of amazing that way. It can swing huge voltage and source
loads of current without loosing it's composure.
You may well find a tube that you like the sound of better than the 7788,
but you will not find a more linear driver or one so robust.
My experience is only with IT coupling though. I don't know how it will
sound RC coupled.
- -grego
PS. Pat, if you haven't gotten 600A settings for the 7788 by Friday, drop
me a note at grego@europa.com and I will work them out for you. Can't do
it until this weekend though.
> Thanks and Regards,
> [ Johari Yip ]
> hfyip@pacific.net.sg
>
> -----Original Message-----
> From: Robert Root <rrjlife@earthlink.net>
> To: sound@deliverator.io.com <sound@deliverator.io.com>
> Date: Monday, August 10, 1998 11:54 AM
> Subject: 7788 as driver:
>
>
> >One of my friends has reworked his 300B amp. He has been using
> > the Tango NY-15 Ni for some time and finds it more detailed than
> > past units. I sent him some 6CJ3's and with his LCLC network is more
> > detailed with better bass. He is using We-300B's at 410volta/60ma.
> > He has tried various drivers, but changed to the 437A. He is using
> > Tads with 416-8B in Onken for the bass. He likes the 437, but tried
> > his trusty 7788-triode connected and is really elated with the
> > results. The 7788 is cap coupled to the 300B by an AN 0.22 copper/oil
> > He runs the 7788 at 210volts/7ma and claims high output and good
> > sensitivity with this setup. Could this really be?
yes
=========================================================================
From: Joseph Lowe <jlowe@cdc.net>
Subject: Re: 7788 as driver:
Date: Mon, 10 Aug 1998 20:04:16 -0400 (EDT)
Source: Sound Digest Archive v01.n383
On Sun, 9 Aug 1998, Robert Root wrote:
> He likes the 437, but tried
> his trusty 7788-triode connected and is really elated with the
> results. The 7788 is cap coupled to the 300B by an AN 0.22 copper/oil
> He runs the 7788 at 210volts/7ma and claims high output and good
> sensitivity with this setup. Could this really be?
>
I am listening to 7788's driving Svet 300B's (B.B. King L.A. Midnight on
vinyl right now). Lots of detail and punch. They could care less about the
input C of a 300B, and can push some serious grid current if need be.
I am running them at 125V 25Ma. Nicad biased. They are IT coupled to the
300B grid through a 1:2 IT. This setup will drive anything including an
845 under full steam. Never had much luck using them R-C though.
=========================================================================
From: "Johari Yip" <hfyip@pacific.net.sg>
Subject: Re: 7788 as driver:
Date: Mon, 10 Aug 1998 23:40:40 +0700
Source: Sound Digest Archive v01.n383
Hi guys,
Robert, you must have read my mind. I'm also contemplating on using the 7788
as driver for my SE 845 running low and hot. 450V at 80mA is what the 845 is
going to have. I would like to know whether the 7788, triode connected, will
be a good driver for this particular task? Appreciate your views.
Thanks and Regards,
[ Johari Yip ]
hfyip@pacific.net.sg
- -----Original Message-----
From: Robert Root <rrjlife@earthlink.net>
To: sound@deliverator.io.com <sound@deliverator.io.com>
Date: Monday, August 10, 1998 11:54 AM
Subject: 7788 as driver:
>One of my friends has reworked his 300B amp. He has been using
> the Tango NY-15 Ni for some time and finds it more detailed than
> past units. I sent him some 6CJ3's and with his LCLC network is more
> detailed with better bass. He is using We-300B's at 410volta/60ma.
> He has tried various drivers, but changed to the 437A. He is using
> Tads with 416-8B in Onken for the bass. He likes the 437, but tried
> his trusty 7788-triode connected and is really elated with the
> results. The 7788 is cap coupled to the 300B by an AN 0.22 copper/oil
> He runs the 7788 at 210volts/7ma and claims high output and good
> sensitivity with this setup. Could this really be?
>
=========================================================================
From: "Johari Yip" <hfyip@pacific.net.sg>
Subject: Re: 7788 as driver:
Date: Tue, 11 Aug 1998 08:42:35 +0800
Source: Sound Digest Archive v01.n383
Thanks Grego for your view. Tells you that I've yet to catch a glimpse of
the latest SP. Appreciate it.
Cheers,
Johari Yip
[ hfyip@pacific.net.sg ]
- ----------
> From: Grego Sanguinetti <grego@lscpdx.latticesemi.com>
> To: sound@deliverator.io.com
> Subject: Re: 7788 as driver:
> Date: Tuesday, August 11, 1998 1:50 AM
> Not directed to me, but I will butt in anyway.
>
> Yes, I have used 845s in the B52 amp. There the 7788 is going through
> a 1:2 IT.
>
> The 7788 in triode mode has a mu of about 56 and a measured Rp of about
1k3.
> It will survive at 210v Vp at 51mA!! I know, I ran it that way for a
while.
> However it does not require lots of current to sound nice, as indicated
> by Robert's friend's operating point.
>
> Which leads me to a note about the 7788 driver in the SP15 article. There
> is a mistake on the schematic. The schematic shows the model number for
the
> modified 2K IT, however the indicated current for the driver is for the
> stock 5K IT. With the 2K IT the driver runs close to 50mA for some
7788's.
>
> When running with the 2K IT, I swapped the lower 0C3 for an 0A3 (wild
looking)
> to reduce the Vp to about 180v. That drops the current to about 17mA.
> Sounds fine that way.
>
> The measured distortion with this driver (which is VERY low!) varies
little
> with current and operating point, compared with other such tubes I have
> checked out. Kind of amazing that way. It can swing huge voltage and
source
> loads of current without loosing it's composure.
>
> You may well find a tube that you like the sound of better than the 7788,
> but you will not find a more linear driver or one so robust.
>
> My experience is only with IT coupling though. I don't know how it will
> sound RC coupled.
>
> -grego
>
>
> PS. Pat, if you haven't gotten 600A settings for the 7788 by Friday, drop
> me a note at grego@europa.com and I will work them out for you. Can't do
> it until this weekend though.
=========================================================================
From: Grego Sanguinetti <grego@lscpdx.latticesemi.com>
Subject: Re: 7788 as driver:
Date: Tue, 11 Aug 1998 10:39:25 -0700
Source: Sound Digest Archive v01.n384
> Joe Lowe, knows his stuff. I believe him. He is using a step up tranny.
> Much respected, Grego is also running a step up tranny. So what gives?
Flattery alert.
> design criteria?
>
> Well, (1) the driver must have a low enough output impedance be able to
> match well with the input impedance of the output stage, (2) the driver
> must be able to deal with the Miller effect associated with the output
> tube, and (3) the driver must be able to swing enough voltage. There is
> something else too; but, this is a basic idea.
Yes there are others, besides sound of course, as I will get too.
> I've had a ton of experience with the 417/5842 as a driver and in SE
> configuration as a one tube amp. To me, it doesn't cut it. It has the
> current and the low impedance; but, it lacks the voltage swing. Used
I also went through the 5842 after hearing about it from guys here on the
list. I still think it is a fine tube but voltage was definately the
problem. But not just output swing. Input swing was an issue also. I
couldn't find a usable bias point above around 1.7v and that just wasn't
enough for my systems, as a driver tube anyway. So I moved on to others
like the 6J4WA (great sounding tube).
> forget it. The 437 is more of the same. Perhaps this is why Joe and
> Grego go with the step up trannies. Let's look one step further.
Sure, I needed more swing and didn't want another tube stage.
> Suppose for a moment that I'm right and that you are asking the 5842 for
> swing and that it approaches nonlinearity. One would expect that if you
> put an inherently more linear tube (triode wired 7788) in its place
> things would improve. Is this what Robert's friend found? I bet it is.
> Is this why Grego goes with the 7788? I bet it is.
Initially because it was because it had more flexible operating points.
Along time ago some Ham friends had told me about the 7788 and gave
me a couple of used ones. They thought I should use them in my guitar
amps. It didn't really work out and then I found out how expensive they
were. This was when they were still made and they cost a fortune!
Then Lowe and behold (sorry, couldn't resist B^), Joe talks about using
it as a HiFi driver. Damn yes, that's the ticket. So I dug them up and
sure enough, as Joe said, loaded with an IT (or choke) they kick major
ass. My test set up said they were like no distortion so I called up
Matt Kamna and hauled one over, with one of my Sowter 5K IT's and set
up a test with his test gear (better than mine). Man, we were blown
away. We got the silly little thing to pump out 450v (with the IT in
1:2 mode) before it started to visually clip!!! We probably could have
done even better if we had rebiased for a higher plate voltage.
Maybe it was the beer but we started hoppin' around and acted pretty silly.
Nerds in heaven and the pearly gates had Amperex across them!
> So why do people build two stage amps? Is it less complicated? Is it
> easier to understand?
Simple, after a few beers, you can still trace the wiring.
> Probably. Is it why people lust for interstage
> transformers? Could be; but, I doubt this one. Let me share something I
> found with those lurking, I was running a 5842 SE amp. I built an
> independent 71A stage with its own power supply. I then choke loaded the
> 5842 and cap coupled to the 71A stage. Now I had the direct heated
> sound. (A side note here is that I bet Tom Ronan's 26 line stage with the
> 5842 SE amp assimilates a direct heated output stage amp sonically) I
> put in some interstage transformers. Things improved. Then I dispensed
> with the 5842 and use a single stage capable of some voltage swing. WOW!
> Granted, I didn't quite have the gain; but, the sonics were much
> improved. My conclusion, it takes three stages. Plus this allows the
> use of low mu tubes... :>)
...Kind of getting distracted by someone who wants me to work for a
living, but I am not sure I see your point here?
- -grego
=========================================================================
From: ldmo@cbmaila.cb.lucent.com
Subject: RE: 7788 as driver:
Date: 11 Aug 98 10:41:00 -0400
Source: Sound Digest Archive v01.n384
Gang:
I'm sorry I haven't had much time to contribute lately; but, allow me to
present some thoughts I've had on this post.
Joe Lowe, knows his stuff. I believe him. He is using a step up tranny.
Much respected, Grego is also running a step up tranny. So what gives?
What are we really trying to achieve. In other words, what are our
design criteria?
Well, (1) the driver must have a low enough output impedance be able to
match well with the input impedance of the output stage, (2) the driver
must be able to deal with the Miller effect associated with the output
tube, and (3) the driver must be able to swing enough voltage. There is
something else too; but, this is a basic idea.
I've had a ton of experience with the 417/5842 as a driver and in SE
configuration as a one tube amp. To me, it doesn't cut it. It has the
current and the low impedance; but, it lacks the voltage swing. Used
within its limitations it is good; but, ask it to swing some voltage and
forget it. The 437 is more of the same. Perhaps this is why Joe and
Grego go with the step up trannies. Let's look one step further.
Suppose for a moment that I'm right and that you are asking the 5842 for
swing and that it approaches nonlinearity. One would expect that if you
put an inherently more linear tube (triode wired 7788) in its place
things would improve. Is this what Robert's friend found? I bet it is.
Is this why Grego goes with the 7788? I bet it is.
So why do people build two stage amps? Is it less complicated? Is it
easier to understand? Probably. Is it why people lust for interstage
transformers? Could be; but, I doubt this one. Let me share something I
found with those lurking, I was running a 5842 SE amp. I built an
independent 71A stage with its own power supply. I then choke loaded the
5842 and cap coupled to the 71A stage. Now I had the direct heated
sound. (A side note here is that I bet Tom Ronan's 26 line stage with the
5842 SE amp assimilates a direct heated output stage amp sonically) I
put in some interstage transformers. Things improved. Then I dispensed
with the 5842 and use a single stage capable of some voltage swing. WOW!
Granted, I didn't quite have the gain; but, the sonics were much
improved. My conclusion, it takes three stages. Plus this allows the
use of low mu tubes... :>)
Robert, have your friend remove one LC section in the output stage power
supply and build an independent power supply for the input stage which is
CLC using a low value choke. Then tell me what you think. wink!
Just some thoughts,
L.D. Moore
-----Original Message-----
From: owner-sound [SMTP:owner-sound@lists.io.com]
Sent: Monday, August 10, 1998 8:04 PM
To: Robert Root
Cc: sound
Subject: Re: 7788 as driver:
On Sun, 9 Aug 1998, Robert Root wrote:
> He likes the 437, but tried
> his trusty 7788-triode connected and is really elated with the
> results. The 7788 is cap coupled to the 300B by an AN 0.22 copper/oil
> He runs the 7788 at 210volts/7ma and claims high output and good
> sensitivity with this setup. Could this really be?
>
I am listening to 7788's driving Svet 300B's (B.B. King L.A. Midnight on
vinyl right now). Lots of detail and punch. They could care less about
the
input C of a 300B, and can push some serious grid current if need be.
I am running them at 125V 25Ma. Nicad biased. They are IT coupled to the
300B grid through a 1:2 IT. This setup will drive anything including an
845 under full steam. Never had much luck using them R-C though.
=========================================================================
From: Joseph Lowe <jlowe@cdc.net>
Subject: RE: 7788 as driver:
Date: Tue, 11 Aug 1998 21:10:18 -0400 (EDT)
Source: Sound Digest Archive v01.n385
On 11 Aug 1998 ldmo@cbmaila.cb.lucent.com wrote:
> Gang:
> (2) the driver
> must be able to deal with the Miller effect associated with the output
> tube, and (3) the driver must be able to swing enough voltage. There is
> something else too; but, this is a basic idea.
These two things are seriously intertwined. The miller effect is very
pronounced with tubes in the 417 family. High grid - plate C with high Mu,
a bad combination. To further complicate things the load impedance
reflected back to the grid gets twisted every which way which when dealing
with the Miller effect. RDH 3 (not 4) has a complete treatment of the
subject.
The input C of a 7788, even triode connected, is WAY lower than a 417,
greatly reducing the Miller effect. Also keep in mind that the 417 was
designed for grounded grid RF service where grid - plate C is not a
problem. The 7788 on the other hand was designed for grounded cathode
video bandwidth apps. The most famous application for them was the Vert.
outputs in 70's vintage Tek Video waveform monitors.
You guys that are running them beyond their ratings will discover that
they have a habit of going flat all of a sudden. That was the falure mode
in the Tek scopes where they ran them blazing hot to get that last few
Mhz of bandwidth. Don't think you are getting away with something.
=========================================================================
From: Joseph Lowe <jlowe@cdc.net>
Subject: Re: 7788 as driver:
Date: Tue, 11 Aug 1998 21:21:20 -0400 (EDT)
Source: Sound Digest Archive v01.n385
On Tue, 11 Aug 1998, Grego Sanguinetti wrote:
> We got the silly little thing to pump out 450v (with the IT in
> 1:2 mode) before it started to visually clip!!! We probably could have
> done even better if we had rebiased for a higher plate voltage.
> Maybe it was the beer but we started hoppin' around and acted pretty silly.
> Nerds in heaven and the pearly gates had Amperex across them!
The first time I saw the voltage from an IT coupled 7788, I thought
something was seriously wrong with the test setup! How the Hell can a
tube with 150 V on the plate be putting out 375V???
=========================================================================
From: "J. Gordon Rankin" <waudio@cinti.net>
Subject: Re: 7788 as driver:
Date: Wed, 12 Aug 98 11:17:22 -0500
Source: Sound Digest Archive v01.n385
Grego & Company;
>> forget it. The 437 is more of the same. Perhaps this is why Joe and
>> Grego go with the step up trannies. Let's look one step further.
I agree with the comment on the 417A, never enough. But I have to
disagree about the 437A, man this is easily 3 417A's in the same bottle.
I get tons of V swing and really low Rp (typically less than 1K at 20ma).
I just got a fax of the review of my Triton-300B Signatures that uses a
437A IT->300B by Larry Kay of Fi and he was stunned. Actually I think it
was some of the best work I had heard to date.
> >The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
> >It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
Now does anyone have any curves for the 7788 triode connected? What is
the max wattage and max cathode current? Does the Rp change significantly
with current? To get an Rp of 1300 what current does the tube need to be
biased at?
Thanks in advance as always!
Gordon
=======> Wavelength Audio <=======
mailto:waudio@cinti.net
http://www.wavelengthaudio.com
ph.fx. 513-271-4186 USA
=========================================================================
From: Grego Sanguinetti <grego@lscpdx.latticesemi.com>
Subject: Re: 7788 as driver:
Date: Wed, 12 Aug 1998 13:22:17 -0700
Source: Sound Digest Archive v01.n386
On Wed, Aug 12, 1998 at 11:17:22AM -0500, J. Gordon Rankin wrote:
> I agree with the comment on the 417A, never enough. But I have to
> disagree about the 437A, man this is easily 3 417A's in the same bottle.
> I get tons of V swing and really low Rp (typically less than 1K at 20ma).
> I just got a fax of the review of my Triton-300B Signatures that uses a
> 437A IT->300B by Larry Kay of Fi and he was stunned. Actually I think it
> was some of the best work I had heard to date.
cool, then by all means try out the 7788 and let us know how you
think they compare. Both fine tubes of course, in the top of the breed.
The 7788 is, at least at this point, cheaper by half.
> > >The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
> > >It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
>
> Now does anyone have any curves for the 7788 triode connected? What is
> the max wattage and max cathode current? Does the Rp change significantly
> with current? To get an Rp of 1300 what current does the tube need to be
> biased at?
sorry that I don't have any data at work and I don't have
any hardcopy curves.
As I recall the max Pd was 5w?
max Vp is 400v
Didn't take Rp at varing current, just at the particular
op point of interest so don't have delta data. I still don't
have any power in the shop so further data will have to
wait. Also my Rp was a back of matchbook calculation while
we were hooting over the distortion. It should not be considered
super reliable data at this point.
The Rp of 1K3 was measured with 30-35mA (can't recall exactly).
- -grego
=========================================================================
From: Darrell Whitfield <dwhitf@swbell.net>
Subject: Re: 7788 as driver:
Date: Wed, 12 Aug 1998 16:39:53 -0500
Source: Sound Digest Archive v01.n386
I have the data sheets for the 7788 and I just got a scanner but I'm inexperience
with it,if someone would like to scan the sheets and put them on the net for
everyone I'll snail it to you.Otherwise I'll give it a try and post them this
weekend if there is any interest.
Later
Darrell
J. Gordon Rankin wrote:
> Grego & Company;
>
> >> forget it. The 437 is more of the same. Perhaps this is why Joe and
> >> Grego go with the step up trannies. Let's look one step further.
>
> I agree with the comment on the 417A, never enough. But I have to
> disagree about the 437A, man this is easily 3 417A's in the same bottle.
> I get tons of V swing and really low Rp (typically less than 1K at 20ma).
> I just got a fax of the review of my Triton-300B Signatures that uses a
> 437A IT->300B by Larry Kay of Fi and he was stunned. Actually I think it
> was some of the best work I had heard to date.
>
> > >The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
> > >It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
>
> Now does anyone have any curves for the 7788 triode connected? What is
> the max wattage and max cathode current? Does the Rp change significantly
> with current? To get an Rp of 1300 what current does the tube need to be
> biased at?
>
> Thanks in advance as always!
> Gordon
>
> =======> Wavelength Audio <=======
> mailto:waudio@cinti.net
> http://www.wavelengthaudio.com
> ph.fx. 513-271-4186 USA
=========================================================================
From: Paul Joppa <pdj@ISDNseattle.net>
Subject: Re: 7788 as driver:
Date: Wed, 12 Aug 1998 23:06:11 -0700
Source: Sound Digest Archive v01.n387
This was a good post, inspired me to the following comments:
ldmo@cbmaila.cb.lucent.com wrote:
...snip...
> Well, (1) the driver must have a low enough output impedance be able to
> match well with the input impedance of the output stage, (2) the driver
> must be able to deal with the Miller effect associated with the output
> tube, and (3) the driver must be able to swing enough voltage. There is
> something else too; but, this is a basic idea.
1 and 2 of the above relate to driver stage output impedance. 3
relates to power, in the context of the other two. A 2:1 interstage
step-up on a 1300-ohm rp 7788 at 210 volts makes it effectively a
5200-ohm rp device at 420 volts. If there were such a beast (gm of
12500) as linear as a triode-connected 7788 it might sound similar -
but I don't know of one. Maybe a 6SN7GTB with paralleled sections, but
that has less gain and less gm ...
> I've had a ton of experience with the 417/5842 as a driver and in SE
> configuration as a one tube amp. To me, it doesn't cut it. It has the
> current and the low impedance; but, it lacks the voltage swing.
Yes - it's a low-impedance 4-watt device, so it can't take much
voltage (spec at 180v).
> ... Used
> within its limitations it is good; but, ask it to swing some voltage and
> forget it. The 437 is more of the same.
Of course - it's twice the current, half the resistance - and the same
voltage limitation.
> ... Perhaps this is why Joe and
> Grego go with the step up trannies. Let's look one step further.
> Suppose for a moment that I'm right and that you are asking the 5842 for
> swing and that it approaches nonlinearity. One would expect that if you
> put an inherently more linear tube (triode wired 7788) in its place
> things would improve. Is this what Robert's friend found? I bet it is.
> Is this why Grego goes with the 7788? I bet it is.
Has anyone compared 5842 with a step-up transformer? At 1.5 ratio it
has about the same source impedance as a 7788 at 2:1 step-up. To be
fair, run the 5842 at 180 v and the 7788 at 135v so the power
dissipation and voltage capability and effective impedance are all
similar.
> So why do people build two stage amps? Is it less complicated? Is it
> easier to understand?
Partly based on two theories: 1) fewer stages means less high-order
distortion - more stages has the same effect as feedback in that way.
2) fewer caps in the signal path.
... I snipped the rest; had nothing to contribute there.
- -Paul Joppa
=========================================================================
From: "Johari Yip" <hfyip@pacific.net.sg>
Subject: Re: 7788 as driver:
Date: Thu, 13 Aug 1998 08:36:52 +0800
Source: Sound Digest Archive v01.n387
Thanks Darrell, That's great.
Cheers,
Johari Yip
[ hfyip@pacific.net.sg ]
- ----------
> From: Darrell Whitfield <dwhitf@swbell.net>
> To: J. Gordon Rankin <waudio@cinti.net>
> Cc: Sound Practices MAIL LIST <sound@deliverator.io.com>
> Subject: Re: 7788 as driver:
> Date: Thursday, August 13, 1998 5:39 AM
>
> I have the data sheets for the 7788 and I just got a scanner but I'm
inexperience
> with it,if someone would like to scan the sheets and put them on the net
for
> everyone I'll snail it to you.Otherwise I'll give it a try and post them
this
> weekend if there is any interest.
>
> Later
>
> Darrell
>
> J. Gordon Rankin wrote:
>
> > Grego & Company;
> >
> > >> forget it. The 437 is more of the same. Perhaps this is why Joe and
> > >> Grego go with the step up trannies. Let's look one step further.
> >
> > I agree with the comment on the 417A, never enough. But I have to
> > disagree about the 437A, man this is easily 3 417A's in the same
bottle.
> > I get tons of V swing and really low Rp (typically less than 1K at
20ma).
> > I just got a fax of the review of my Triton-300B Signatures that uses a
> > 437A IT->300B by Larry Kay of Fi and he was stunned. Actually I think
it
> > was some of the best work I had heard to date.
> >
> > > >The 7788 in triode mode has a mu of about 56 and a measured Rp of
about 1k3.
> > > >It will survive at 210v Vp at 51mA!! I know, I ran it that way for a
while.
> >
> > Now does anyone have any curves for the 7788 triode connected? What is
> > the max wattage and max cathode current? Does the Rp change
significantly
> > with current? To get an Rp of 1300 what current does the tube need to
be
> > biased at?
> >
> > Thanks in advance as always!
> > Gordon
> >
> > =======> Wavelength Audio <=======
> > mailto:waudio@cinti.net
> > http://www.wavelengthaudio.com
> > ph.fx. 513-271-4186 USA
>
>
=========================================================================
From: Darrell Whitfield <dwhitf@swbell.net>
Subject: Re: 7788 as driver:
Date: Thu, 13 Aug 1998 11:47:37 -0500
Source: Sound Digest Archive v01.n387
Grego Sanguinetti wrote:
> On Wed, Aug 12, 1998 at 04:39:53PM -0500, Darrell Whitfield wrote:
> > I have the data sheets for the 7788 and I just got a scanner but I'm inexperience
> > with it,if someone would like to scan the sheets and put them on the net for
> > everyone I'll snail it to you.Otherwise I'll give it a try and post them this
> > weekend if there is any interest.
> >
> > Later
> >
> > Darrell
>
> I have a good scanner, but by the time you got them to me
> you could have already done it this weekend. Besides, this
> will be a good oportunity to learn the scanner right!
>
> give it a try.
>
> -grego
Thanks for a word of encouragement Grego,but I don't have time to read the manual this
week I'll be ready next time. I prority-mailed Scott Grammer and Dave Stagner they seem
to be with-in 8 hours of St.Louis (I think) so maybe they will have them this
weekend.The real hero here is Thomas Dunker who mail them to me from Norway. (nice guy)
Have a nice day
Darrell
=========================================================================
From: tubesguy@mail.execpc.com (Patrick Currie)
Subject: 7788 as one-tuber
Date: Tue, 11 Aug 1998 07:57:19 -0500
Source: Sound Digest Archive v01.n384
>The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
>It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
>-grego
Ladies and gentlemen -
I believe we have our candidate for the ultimate spud amp - 2 or maybe 3
watts out at this operating point! Hmm, maybe I'll hold onto those
Brooklyn chokes, at least thru the weekend. - Pat
Pat Currie (tubesguy@execpc.com)
=========================================================================
From: Dave Stagner <dstagner@icarus.net>
Subject: Re: 7788 as one-tuber
Date: Tue, 11 Aug 1998 10:14:41 -0500 (CDT)
Source: Sound Digest Archive v01.n384
On Tue, 11 Aug 1998, Patrick Currie wrote:
> >The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
> >It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
>
> I believe we have our candidate for the ultimate spud amp - 2 or maybe 3
> watts out at this operating point! Hmm, maybe I'll hold onto those
> Brooklyn chokes, at least thru the weekend. - Pat
Y'know, i was thinking exactly the same thing... damn! I think i gotta
find me a pair...
- -dave
Practice beautiful randomness and act kind of senseless.
<dstagner@icarus.net>
=========================================================================
From: ldmo@cbmaila.cb.lucent.com
Subject: RE: 7788 as one-tuber
Date: 11 Aug 98 10:42:00 -0400
Source: Sound Digest Archive v01.n384
Beautiful thought Pat! DO IT!
L.D. Moore
-----Original Message-----
From: owner-sound [SMTP:owner-sound@lists.io.com]
Sent: Tuesday, August 11, 1998 7:57 AM
To: sound
Subject: 7788 as one-tuber
>The 7788 in triode mode has a mu of about 56 and a measured Rp of about
1k3.
>It will survive at 210v Vp at 51mA!! I know, I ran it that way for a
while.
>-grego
Ladies and gentlemen -
I believe we have our candidate for the ultimate spud amp - 2 or maybe 3
watts out at this operating point! Hmm, maybe I'll hold onto those
Brooklyn chokes, at least thru the weekend. - Pat
Pat Currie (tubesguy@execpc.com)
=========================================================================
From: Joseph Lowe <jlowe@cdc.net>
Subject: Re: 7788 as one-tuber
Date: Tue, 11 Aug 1998 20:38:24 -0400 (EDT)
Source: Sound Digest Archive v01.n385
On Tue, 11 Aug 1998, Patrick Currie wrote:
> I believe we have our candidate for the ultimate spud amp - 2 or maybe 3
> watts out at this operating point! Hmm, maybe I'll hold onto those
> Brooklyn chokes, at least thru the weekend. - Pat
Try this sometime: Choke loaded 7788 cap coupled to your >300 Ohm
headphones with a 1K series resistor. I assure you it will be the best
headphone amp you have ever heard. Play around with the resistor
value. It is a balancing act between output voltage swing and distortion.
The distortion spectra of this setup is very nice, about .2% H2, with very
little third and almost unmeasurable higher harmonics. The 50,000 Gm of
the 7788 gives very detailed low level information.
How about real headphone jack on your power amp?
=========================================================================
From: MHuber@t-online.de (Manfred Huber)
Subject: Re: 7788 as one-tuber
Date: Tue, 11 Aug 1998 22:16:20 +0100
Source: Sound Digest Archive v01.n385
>I believe we have our candidate for the ultimate spud amp
Good idea!
You may also want to have a look at the EC8020.
Noval base
Pa max=8W
Up max=300V
Ip max=70mA
mu=55
Rp=900 Ohms
I once tried this tube as a driver. The operating point
was at about 260V/30mA with Ug=-3.4V. With an 1:1 IT on
the anode I managed to get out clean 400Vpp. With this kind of swing
and an output impedance of 900 Ohms this driver kicks ass.
The EC8020 was intended as a UHF output triode in grounded
grid mode. With a gm of 60000 !!! it just *loves* to oscillate <g>
I can offer hand-drawn plate curves for this tube if
someone is interested.
Manfred
- ------------------
Manfred Huber
MHuber@t-online.de
- ------------------
=========================================================================
From: Paul Joppa <pdj@ISDNseattle.net>
Subject: Re: 7788 as one-tuber
Date: Tue, 11 Aug 1998 22:39:23 -0700
Source: Sound Digest Archive v01.n385
Patrick Currie wrote:
>
> >The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
> >It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
>
> >-grego
>
> Ladies and gentlemen -
>
> I believe we have our candidate for the ultimate spud amp - 2 or maybe 3
> watts out at this operating point! Hmm, maybe I'll hold onto those
> Brooklyn chokes, at least thru the weekend. - Pat
That's pretty hot - you won't get much efficiency at that point. Plus
it exceeds the rated dissipation by nearly 100%. At 210 volts, you'll
actually get more output at 35mA with a 2500-3000 ohm load. Max rated
screen voltage is 200v, but maybe triode-wired you can go a little
more?
- -Paul Joppa
=========================================================================
From: Grego Sanguinetti <grego@lscpdx.latticesemi.com>
Subject: Re: 7788 as one-tuber
Date: Wed, 12 Aug 1998 13:08:59 -0700
Source: Sound Digest Archive v01.n386
On Tue, Aug 11, 1998 at 10:39:23PM -0700, Paul Joppa wrote:
> > >The 7788 in triode mode has a mu of about 56 and a measured Rp of about 1k3.
> > >It will survive at 210v Vp at 51mA!! I know, I ran it that way for a while.
> >
> > >-grego
>
> That's pretty hot - you won't get much efficiency at that point. Plus
> it exceeds the rated dissipation by nearly 100%. At 210 volts, you'll
> actually get more output at 35mA with a 2500-3000 ohm load. Max rated
> screen voltage is 200v, but maybe triode-wired you can go a little
> more?
Actually I wasn't suggesting that as an operating point.
I reset my plate voltage very soon after that. But I did
run it that way for a while just to see how they held up.
It did fine. But I would heed Joe's warning and keep within spec.
- -grego
=========================================================================
From: evaguido <EvaGuido@iaehv.nl>
Subject: Re: 7788 as one-tuber
Date: Wed, 12 Aug 1998 19:34:32 +0200
Source: Sound Digest Archive v01.n386
Just for the record: E55L (pentode) works as well: gm = 55 mA/V, do not
know Rp as triode though.
Guido
At 20:38 11-8-98 -0400, Joseph Lowe wrote:
>On Tue, 11 Aug 1998, Patrick Currie wrote:
>
>> I believe we have our candidate for the ultimate spud amp - 2 or maybe 3
>> watts out at this operating point! Hmm, maybe I'll hold onto those
>> Brooklyn chokes, at least thru the weekend. - Pat
>
>Try this sometime: Choke loaded 7788 cap coupled to your >300 Ohm
>headphones with a 1K series resistor. I assure you it will be the best
>headphone amp you have ever heard. Play around with the resistor
>value. It is a balancing act between output voltage swing and distortion.
>
>The distortion spectra of this setup is very nice, about .2% H2, with very
>little third and almost unmeasurable higher harmonics. The 50,000 Gm of
>the 7788 gives very detailed low level information.
>
>How about real headphone jack on your power amp?
>
>
>
>
>
=========================================================================
From: Dave Stagner <dstagner@icarus.net>
Subject: Re: 7788 curves; I missed 'em
Date: Mon, 24 Aug 1998 21:30:26 -0500 (CDT)
Source: Sound Digest Archive v01.n400
Don't remember who got the curves up first, but i have them up too.
http://www.spnz.org/selfbias/tubes/7788/
- -dave
Practice beautiful randomness and act kind of senseless.
<dstagner@icarus.net>
=========================================================================
From: "Sellek, Grant (TSA)" <Grant.Sellek@roads.sa.gov.au>
Subject: 7788 curves; I missed 'em
Date: Tue, 25 Aug 1998 09:14:54 +0930
Source: Sound Digest Archive v01.n400
Hi gang, I saw mention posted of people having the 7788 curves, but I missed
the earlier posts. Was it a WWW address? Was it a file someone was posting
out? Did it include a curve for triode-mode?
TIA,
Grant
Grant Sellek
Adelaide, Australia
grant.sellek@roads.sa.gov.au
=========================================================================
From: Tom Ronan <tronan@orion.it.luc.edu>
Subject: 7788 operating points
Date: Wed, 08 Jul 1998 13:40:45 -0500
Source: Sound Digest Archive v01.n336
Here are a few points of data for you folks who want to use the 7788 triode
wired:
Tube #1
152 v plate 2.2v 9.6mA
130 v plate 2.2V 14.3mA
155 v plate 3V 17mA
Tube #2
153 v plate 2.5V 19.5 mA
128 v plate 2.9V 16.4mA
I think I've got these sorted correctly between the tubes...either way it
should give you some data to work wtih. Unfortunately, I've been unable to
get the tube to bias much higher at these voltages, no matter what I did.
Next I'll try some higher voltages to see if I can get a higher bias. I
just want 4 volts from the thing, but it biases at 13.5V in pentode mode at
35mA! Am I wrong in thinking that if a tube biases at 20mA and 2.5V at
153V plate in triode wired mode, then I can (while maintaining the current
at 20mA) increase both the plate voltage and the bias to get my desired
result of 4 volts bias?
It's a shame I dont have curves for these...
Tom
- ----------------------------------------
Tom Ronan 1045 W. Montana
773.528.0882 Chicago, IL 60614
Lowther America - Chicago Representative
=========================================================================
From: Sridhar Gantimahapatruni <Ganti@acta.com>
Subject: 7788 tube data
Date: Wed, 23 Dec 1998 10:26:56 -0800
Source: Sound Digest Archive v01.n550
I was wondering if anybody out there has data on 7788 tube. Please reply
to my home email address which is ganti@ix.netcom.com
Thanks
ganti
=========================================================================
From: pjbone@juno.com (Peter J. Boser)
Subject: 78 tips
Date: Thu, 8 Jan 1998 15:04:20 -0500
Source: Sound Digest Archive v01.n156
I'm sending this to a number of lists in the hope of reaching a maximum
audience -- sorry if it's a bit off topic for some.
Does anyone have any suggestions for a preamp for 78 rpm records? I
don't have much knowledge about them, but it looks to me like there was a
period where some (mostly mono?) preamps had options for different
equalization curves, filters, etc. Cheap would be a priority, and so
would realistic availability, but I guess I could live with a quest for a
while. Does anybody know what models I should look for?
I would also be willing to think about a mono integrated amp (or
receiver, I suppose) if anyone knows of any I should be looking for.
While we're at it, how about suggested 78 rpm turntables and cartridges.
I can make my VPI go 78 with the PLC(dedicated line conditioner which can
dial in oscillation frequency), but I don't have a suitable stylus
(although I have a Shure V15V, for which I think one's available).
The inspiration for all of this is that I bought the IKEA record racks
mentioned by Michael Fremer in _Stereoph*le_, and while re-organizing
records I found I had a bunch more unplayed (by me) dusty 78's than I
thought.
Which brings me to my final (I promise) question -- cleaning 78's. Any
recommendations? I have a Nitty Gritty 1.0 -- does anyone know if that
cool adapter for 45's and 78's fits on mine? What fluid should I use?
Different ones for different types of 78's? Homemade or commercial?
Thanks in advance for any suggestions.
Pete
=========================================================================
From: Tim Reese <reese@nmr.MGH.harvard.EDU>
Subject: Re: 78 tips
Date: Thu, 8 Jan 1998 18:44:04 -0500 (EST)
Source: Sound Digest Archive v01.n156
>Does anyone have any suggestions for a preamp for 78 rpm records? I
>don't have much knowledge about them, but it looks to me like there was a
>period where some (mostly mono?) preamps had options for different
>equalization curves, filters, etc. Cheap would be a priority, and so
>would realistic availability, but I guess I could live with a quest for a
>while. Does anybody know what models I should look for?
Charley Kittelson (via EB) in GA V4 #2 recommends the "mono Scott 121C
if you listen to old records with unusual response curves".
- ---------------------------------------------------------------
Tim Reese, MGH NMR Center reese@nmr.MGH.harvard.edu
Old Engineering Proverb : never calculate what you can measure.
=========================================================================
From: Geoff Armstrong <geofstro@monaco.mc>
Subject: Re: 78 tips
Date: Fri, 9 Jan 1998 09:32:09 +0100
Source: Sound Digest Archive v01.n157
Peter,
Here are two URL's to get you started:
http://www.audio-restoration.com/
http://www.78rpm.com/
http://rogue.northwest.com/~cerasin9/
Geoff Armstrong
The Analogue Domain = The true sound of music!
=========================================================================
From: Plaato <Plaato@aol.com>
Subject: Re: 78 tips
Date: Fri, 9 Jan 1998 23:15:17 EST
Source: Sound Digest Archive v01.n157
<<HI
In a message dated 1/8/98 5:33:34 PM, you wrote:
<<Does anyone have any suggestions for a preamp for 78 rpm records?
I've always used a Macintosh C20. The advantage here is that you can play
either channel in mono. One channel ( in stereo) will often be cleaner
sounding on an old 78. We used to do this with great success in restoring old
Blind Lemon Jefferson 78 records when I was in college.
The C20 came with response curve EQ settings for most major 78 labels to be
used with its own settings. I posted these and others from an old audio
magazine article on 78's to this list about two years ago. I Would be willing
to do so again if there was enough interest. At the very least I would be
happy to mail them to you.
The other nice thing about the C20 is that the high filter settings are in
line with the record out jacks. Useful for making clean recordings.
While we're at it, how about suggested 78 rpm turntables and cartridges.
My favorite 78 setup has always been a Thorens TD124 with a Shure M1
arm/cartridge combo. This was first suggested by Clark Johnson, of PF fame,
who is a local 78 afflictionado here in Boston.
Lately I have been enjoying 78's on an old Rek O Kut Rondine deluxe with a
Thorens arm and Shure m55 cartridge. there's something of a synergy with
direct drive TT's and 78's, I think.
Which brings me to my final (I promise) question -- cleaning 78's. Any
recommendations? >>
Mild ivory soap and warm water. I use a washcloth, and keep the label dry.
Rinse well, then gently towel dry.
Hope this helps.
Henry Platt
>>
=========================================================================
From: "Bottlehead" <Bottlehead@prodigy.net>
Subject: Re: 78 tips
Date: Tue, 13 Jan 1998 09:56:12 -0800
Source: Sound Digest Archive v01.n159
>
> >Does anyone have any suggestions for a preamp for 78 rpm records? I
> >don't have much knowledge about them, but it looks to me like there was
a
> >period where some (mostly mono?) preamps had options for different
> >equalization curves, filters, etc. Cheap would be a priority, and so
> >would realistic availability, but I guess I could live with a quest for
a
> >while. Does anybody know what models I should look for?
>
> Charley Kittelson (via EB) in GA V4 #2 recommends the "mono Scott 121C
> if you listen to old records with unusual response curves".
>
We did a comparison of my stock 121C to a recapped Fisher 50C a few years
back, using a TD124, SME, and Shure SC-35 with 3 mil conical stylus, a
Burwen TNE, and an SAE "click and popper".
The 50C was preferred by most, even though lacking the fine adjustivity and
extra do-dads of the 121, better bass, clearer sounding.
The Scott noise suppressor is pretty crappy compared to the TNE, which is
quite good, reducing a lot of surface noise, though not the big pops,
without taking too much music. The SAE was very good at big scratches, but
not so hot at the surface noise.
All this processing is nice if your 78s are really hosed, and you can
switch it out on the primo stuff.
Actually the TNE would probably be very nice with worn LP's too, after
replacing all the fonky ICs inside with some new age junk.
By the way, *never* hot plug one of these. I smoked mine that way, and
haven't gotten around to fixing it.
And don't forget that big stylus for 78s. Makes a world of difference.
Doc B.
=========================================================================
From: Rick Francis <rfranci@uoft03.UTOLEDO.EDU>
Subject: Re: 78 tips--"hot plug"?
Date: Tue, 13 Jan 1998 14:49:56 -0500 (EST)
Source: Sound Digest Archive v01.n159
On Tue, 13 Jan 1998, Bottlehead wrote:
> By the way, *never* hot plug one of these. I smoked mine that way, and
> haven't gotten around to fixing it.
>
Huh? How do I avoid doing it if I don't know what it is... Hot ground?
Floating ground?
Rick a.k.a. "list idiot"
=========================================================================
From: "Bottlehead" <Bottlehead@prodigy.net>
Subject: Re: 78 tips--"hot plug"?
Date: Tue, 13 Jan 1998 13:53:59 -0800
Source: Sound Digest Archive v01.n160
> > By the way, *never* hot plug one of these. I smoked mine that way, and
> > haven't gotten around to fixing it.
> >
> Huh? How do I avoid doing it if I don't know what it is... Hot ground?
> Floating ground?
>
> Rick a.k.a. "list idiot"
Hot plugging is pulling the cables out of, or plugging them into, a live
system. I pulled the input cables out while the TNE was on, and poof, no
more output. Apparently took out some device in the input stage.
I have an evil, but well earned reputation for this bad habit, which I am
trying to stop since running my PM2As with 20 watt amps.
Doc B.
=========================================================================
From: PJBSLB <PJBSLB@aol.com>
Subject: Re: 78 tips--"hot plug"?
Date: Tue, 13 Jan 1998 23:24:21 EST
Source: Sound Digest Archive v01.n160
In a message dated 98-01-13 17:45:54 EST, you write:
<< running my PM2As with 20 watt amps.>>
20 Watts!!!!!! What are you, some kind of power hungry Phase Linear-
converted SET traitor? ;-)
=========================================================================
From: "Bottlehead" <Bottlehead@prodigy.net>
Subject: Re: 78 tips--"hot plug"?
Date: Wed, 14 Jan 1998 07:38:07 -0800
Source: Sound Digest Archive v01.n160
> << running my PM2As with 20 watt amps.>>
> 20 Watts!!!!!! What are you, some kind of power hungry Phase Linear-
> converted SET traitor? ;-)
No way.
That's 20 SE parafeed VV52 watts, homes.
You want live levels in a good sized room, you gotta pay to play.
Running a super tweeter with the 2As, and a bi amped 96 dB sub (on 25 SE
211 watts) with my Lowthers too. Don't knock it til you try it. Closing in
on Exemplar and Edgarhorn dynamics, but with better extension and midrange
integration.
This all goes back to a concert by the Seattle Symphony last summer. When I
came home from it and listened to my system, I decided that, to reproduce
that kind of music believably, you need some mildly serious power into
something as inefficient as 97-98dB speaks.
Sooo- 45W into a wideband, tonally balanced 97dB or so system works.
2W into a 103 dB system would work too, but wideband and tonally balanced
don't fit into that program quite right. Yet. Getting closer though. Stay
tuned.
Doc B.
=========================================================================
From: el34@juno.com
Subject: Re: 78 tips--"hot plug"?
Date: Wed, 14 Jan 1998 10:10:24 -0500
Source: Sound Digest Archive v01.n160
On Tue, 13 Jan 1998 13:53:59 -0800 "Bottlehead" <Bottlehead@prodigy.net>
writes:
>Hot plugging is pulling the cables out of, or plugging them into, a
>live
>system. I pulled the input cables out while the TNE was on, and poof,
>no
>more output. Apparently took out some device in the input stage.
>I have an evil, but well earned reputation for this bad habit, which I
>am
>trying to stop since running my PM2As with 20 watt amps.
I managed to smoke a sound card in my computer this way when I hot
plugged into a tube preamp. Actually what happened was I let the tip of
the phono plug touch the ring on the preamp. There was a visible spark,
and then an
"ohnosecond" later It started to dawn on me I had just screwed up big
time. I was lucky it only got the sound card!
There were a few tense moments until I made sure everything else still
worked.
A lot of the old tube gear did not use a grounded plug, but instead had
an internal cap from one side of the line to the case. There is a 50/50
chance that you will end up with the case tied to the national power grid
through a .1mf cap!
NEVER connect anything to a computer that does not have a grounded plug.
If you must, measure the voltage difference between the devices first
with a high impedance voltmeter.
=========================================================================
From: Carter Hendricks <carterh@crl.com>
Subject: .7 Watt / 26 pre
Date: Mon, 09 Mar 1998 21:54:41 -0600
Source: Sound Digest Archive v01.n212
Ronan called and said that he'd be in St Louis for the [past]] weekend,
and that he'd bring his 46 amp. I've been listening to a 417 amp with
identical Lucas Cant transformers and I was curious how the two amps
would compare. I borrowed a good CD player [Stanplayer was down,
now fixed] and preamp.
The two amps were interesting together. I think the 46's [temporary? 5687
driver stage] are smoother and more together sounding but that the bass
is less solid and there is a little less clarity than with the 417A tube by
itself.
Fair enough. I'll leave it to Tom to elaborate.
[I wonder how much better the 417A might be with the kind of developed
power supply Tom has in the 46 amp. Remember I've just using the Conrad
Johnson kludge].
What blew me away was the 26 line stage he brought down.
I was building one myself but was wondering just why.
Well, we tried all the combinations we could think of with the equipment
at hand. Including no preamp. The 26 added music and fun. Not some
bull**** veiling thing: pianos sound -wonderful- with the 26. It wasn't
a scientific test, and preparations for Anna's 7th birthday party sorta
interfered with our listening, but the 26 was the other star of the
weekend. 'Should have mine done in a few days...
Tim Reese