[Peter Wieck]

Whilst at Kutztown, I snagged a complete set of Iron from a Fisher
500B, all parts & pieces testing good via a VOM (unproven in a
circuit), but no sign of heat-damage, bad wire, cracking, rust or
otherwise. Rumor has it that this receiver/amp (500B) was not that bad
even if based on the 7591 output tubes. $12.50 for the lot did not seem
like a half-bad price, either.

I am inclined to maybe build an amp over the winter, using this iron,
likely based on 6BQ5/EL84 PP outputs, not sure of any driver
configuration.

What I would also like to include on the same chassis (but a separate
P/S and shielded) is a phono pre-amp. However, this is a separate issue
for the long-run. This will be my first foray into a scratch-project.

I have any number of "name" tubes including several sets of Siemens,
Mullard, Sylvania and Telefunken-branded EL-84 NOS tubes, as well as
lots of various 6 & 12V 9-pin drivers from 7199s through all of the 12
& 6V dual-triodes.

Any suggestions? I would prefer to keep it simple for the first
go-round.

Peter Wieck
Wyncote, PA

[Tom Bavis]

On 23 Sep 2006 18:29:16 -0700, "Peter Wieck" wrote:

Whilst at Kutztown, I snagged a complete set of Iron from a Fisher
500B, all parts & pieces testing good via a VOM (unproven in a
circuit), but no sign of heat-damage, bad wire, cracking, rust or
otherwise. Rumor has it that this receiver/amp (500B) was not that bad
even if based on the 7591 output tubes. $12.50 for the lot did not seem
like a half-bad price, either.

I am inclined to maybe build an amp over the winter, using this iron,
likely based on 6BQ5/EL84 PP outputs, not sure of any driver
configuration.

What I would also like to include on the same chassis (but a separate
P/S and shielded) is a phono pre-amp. However, this is a separate issue
for the long-run. This will be my first foray into a scratch-project.

I have any number of "name" tubes including several sets of Siemens,
Mullard, Sylvania and Telefunken-branded EL-84 NOS tubes, as well as
lots of various 6 & 12V 9-pin drivers from 7199s through all of the 12
& 6V dual-triodes.

Any suggestions? I would prefer to keep it simple for the first
go-round.

Peter Wieck
Wyncote, PA


With the supply voltage and transformer impedance you have, I would
use EL34 or 6L6. 1/2 12AX7 driving a 12BH7 or 6CG7 long-tail
splitter. 6CW5 (EL86) or 6Y6 could be used if you use a full-wave
bridge for 200V instead of a voltage doubler.

Tom Bavis

[Omer Suleimanagich]

Peter,

I would keep the 7591's in it and use a matched set of Slovak JJ's. My
biased Sanasui 1000A sounds like heaven with them!

EL84's don't have the Mojo like the 7591's nor do the EL34's, or 6L6's. To
me , it sounds like putting a VW engine into a 912 Porsche. If anything, I
would like to see one of these units use 6550's or KT90's if you could take
this unit there.

That's just me!

Omer
"Tom Bavis" wrote in message
news:4515fd65.47266578@news-server...
On 23 Sep 2006 18:29:16 -0700, "Peter Wieck" wrote:

Whilst at Kutztown, I snagged a complete set of Iron from a Fisher
500B, all parts & pieces testing good via a VOM (unproven in a
circuit), but no sign of heat-damage, bad wire, cracking, rust or
otherwise. Rumor has it that this receiver/amp (500B) was not that bad
even if based on the 7591 output tubes. $12.50 for the lot did not seem
like a half-bad price, either.

I am inclined to maybe build an amp over the winter, using this iron,
likely based on 6BQ5/EL84 PP outputs, not sure of any driver
configuration.

What I would also like to include on the same chassis (but a separate
P/S and shielded) is a phono pre-amp. However, this is a separate issue
for the long-run. This will be my first foray into a scratch-project.

I have any number of "name" tubes including several sets of Siemens,
Mullard, Sylvania and Telefunken-branded EL-84 NOS tubes, as well as
lots of various 6 & 12V 9-pin drivers from 7199s through all of the 12
& 6V dual-triodes.

Any suggestions? I would prefer to keep it simple for the first
go-round.

Peter Wieck
Wyncote, PA


With the supply voltage and transformer impedance you have, I would
use EL34 or 6L6. 1/2 12AX7 driving a 12BH7 or 6CG7 long-tail
splitter. 6CW5 (EL86) or 6Y6 could be used if you use a full-wave
bridge for 200V instead of a voltage doubler.

Tom Bavis

[Peter Wieck]

Omer Suleimanagich wrote:

If anything, I would like to see one of these units use 6550's or KT90's if you could take this unit there.

That's just me!

I do have a matched quad of NOS Tung-Sol 6550s. And I think I have a
set of unmatched NOS Philips floating around somewhere. But this seems
like a lot for such small OPTs. I was saving the 6550s for the Scott
LK-150, anyway.

I do also have Mullard & GE EL34s, I had not counted on purchasing new
tubes... but I will take this under advisement as I search for
appropriate circuits. Once I do choose output tubes, I will work on the
layout, sheet-metal and spacing as I do not want a mare's nest above or
below the chassis, nor do I want heat problems. I have also been
hoarding some very nice ceramic sockets of all sizes for some years,
some of them equipped with bright nickle-plated flanges and shields
should that need arise.

Thoughts on filtering? I intend to use a bridge rectifier, I have been
thinking of using parallel 2uF, 600V mylars as setting them staggered
on both sides of a glass perf-board below the chassis would not add
much depth, not take up much real-estate relative to the tube layout
and could be neatly shielded "along the back" so to speak.

Alternately, I have a supply of 5AR4s, more 5U4s than should be
considered sane, and so forth. Also various chokes, though none of them
much more than junk-box stuff.

Thanks again for the replies. I am collecting ideas at this point. When
the cold weather sets in and the Honey-dos & such reduce, I will start
collating them to an actual starting point.

[Omer Suleimanagich]

Peter,

What's the issue with 7591's?!

Those tubes came out of the early 60's, the climax of vacuum tube circuitry!

A time when we were figuring out how to send man on the moon.

If you want some more oomph, ask our resident aerospace engineer/tech, Jeff
Angus. The two of us did some amazing things with my Sansui 1000A.

Send Jeff the schematics of the 500B, tell him your music preferences, and
he will help take you to nirvana with that receiver!

Just ask him about some of the seven herbs and spices he uses with the caps.

Ever since Jeff serviced a few guitar amps, folks around here have been
walking away from their bumble bee caps, en masse!

Omer


"Peter Wieck" wrote in message
oups.com...

Omer Suleimanagich wrote:

If anything, I would like to see one of these units use 6550's or KT90's
if you could take this unit there.

That's just me!

I do have a matched quad of NOS Tung-Sol 6550s. And I think I have a
set of unmatched NOS Philips floating around somewhere. But this seems
like a lot for such small OPTs. I was saving the 6550s for the Scott
LK-150, anyway.

I do also have Mullard & GE EL34s, I had not counted on purchasing new
tubes... but I will take this under advisement as I search for
appropriate circuits. Once I do choose output tubes, I will work on the
layout, sheet-metal and spacing as I do not want a mare's nest above or
below the chassis, nor do I want heat problems. I have also been
hoarding some very nice ceramic sockets of all sizes for some years,
some of them equipped with bright nickle-plated flanges and shields
should that need arise.

Thoughts on filtering? I intend to use a bridge rectifier, I have been
thinking of using parallel 2uF, 600V mylars as setting them staggered
on both sides of a glass perf-board below the chassis would not add
much depth, not take up much real-estate relative to the tube layout
and could be neatly shielded "along the back" so to speak.

Alternately, I have a supply of 5AR4s, more 5U4s than should be
considered sane, and so forth. Also various chokes, though none of them
much more than junk-box stuff.

Thanks again for the replies. I am collecting ideas at this point. When
the cold weather sets in and the Honey-dos & such reduce, I will start
collating them to an actual starting point.

[Omer Suleimanagich]

You're thinking of the Porsche 914. That one can take a six cylinder
Porsche engine. The 912's 4 cylinder has few more horsys and is better made
than the VW's four cylinder.

Omer

P. S. Peter has so much equipment, that it would make the retired folks from
the Sarnoff lab wince!


"Bret Ludwig" wrote in message
ps.com...

Omer Suleimanagich wrote:
Peter,

I would keep the 7591's in it and use a matched set of Slovak JJ's. My
biased Sanasui 1000A sounds like heaven with them!

EL84's don't have the Mojo like the 7591's nor do the EL34's, or 6L6's.
To
me , it sounds like putting a VW engine into a 912 Porsche. If anything,
I
would like to see one of these units use 6550's or KT90's if you could
take
this unit there.


The Porsche 912 DOES have (what is in truth) a VW engine! It's the
pushrod flat four albeit with a three piece case. Most 912s have been
upgraded to 911a or had Corvair, rotary, V6 or V8 swaps.

What IS the impedance ratio of these particular transformers? As
actually determined by test and not what anyone else says?

[Peter Wieck]

Omer Suleimanagich wrote:
Peter,

What's the issue with 7591's?!

No real issues, other than I have no NOS versions in-hand... meaning I
would be required to use modern production and/or talk a friend out of
a quad. Jeff I know, that is a good lead.

Thanks again.

Peter Wieck
Wyncote, PA

[Peter Wieck]

Bret Ludwig wrote:

I'd build a working breadboard first, then take it apart and put it on
the nice chassis. I like transmission oil pans or architectural
aluminum offcuts. Some people use cake pans. If you have a rugrat-free
lab the good old actual breadboard has much to recommend it too.

If you don't have a scope, a audio gen, a AF AC voltmeter, and a dummy
load you are not going to succeed and shouldn't start.

I would punch and bend the chassis based on the choice of output tubes,
which would push back to the driver tubes and so forth. Of course it
would be bread-boarded and proven before final assembly, but I would
attempt to modularize the power-supply and get that settled first. I am
leaning to SS rectification, and I can manage some of the disadvantages
of that choice by my choice in caps and other options.

As to scope, dummy-load, AF generator and an AC rms Voltmeter good up
to 100khz, I have all that.

Peter Wieck
Wyncote, PA

[Omer Suleimanagich]

Hi Peter,

The 7591's can be bought for $65.00 at AES, matched! I would suggest
hotrodding the receiver than cannibalizing. I say this, if all knobs, dial
and face plate are intact.

You could place a solid-state stereo decoder and solid-state rectify the
power supply. If the receiver has the wood cabinet, you could place a fan
in back.

Omer

P. S. Thanks for the detailed help with the Pioneer SX110 last June. I got
it to work with an EM84, but I think I will switch it to an EM87. Jeff and
I are currently rebuilding an RCA stereo simulator, so we'll get the decoder
to work on the mark.


"Peter Wieck" wrote in message
ups.com...

Omer Suleimanagich wrote:
Peter,

What's the issue with 7591's?!

No real issues, other than I have no NOS versions in-hand... meaning I
would be required to use modern production and/or talk a friend out of
a quad. Jeff I know, that is a good lead.

Thanks again.

Peter Wieck
Wyncote, PA

[Peter Wieck]

Omer.....

I snagged the Iron.... no receiver attached. So, anything I do at this
point brings them back to utility.

Peter Wieck
Wyncote, PA

[Chris Hornbeck]

On 24 Sep 2006 17:41:03 -0700, "Peter Wieck" wrote:

I snagged the Iron.... no receiver attached. So, anything I do at this
point brings them back to utility.

A good initial sanity-check is to add up heater currents,
and hopefully to derate the poor old guy a little. You
don't have the economic constraints of the OEM, so can
afford to be generous to a forty year old power
transformer.

EL84's match to a higher load impedance than the OPT
provides, so speaker choice will be critical, but not
impossible. 3dB steps aren't the end of the world,
anyway.

The 6L6 family matches to the OPT's very well, and
with very little heater current penalty.

My personal direction would be triode-connected octals
from the 6L6 family, "fixed" (adjustable by pot) bias
and a really nice driver stage that you've fancied
trying for years, whatever that is. Patrick's web
site has a very well worked out example of a good'un.
But that's just me.

Remember also that line voltages today are *much* higher
than the power transformer was designed for.

Much thanks, as always, and have fun,

Chris Hornbeck

[John Byrns]

In article ,
Chris Hornbeck wrote:

On 24 Sep 2006 17:41:03 -0700, "Peter Wieck" wrote:

I snagged the Iron.... no receiver attached. So, anything I do at this
point brings them back to utility.

A good initial sanity-check is to add up heater currents,
and hopefully to derate the poor old guy a little. You
don't have the economic constraints of the OEM, so can
afford to be generous to a forty year old power
transformer.

EL84's match to a higher load impedance than the OPT
provides, so speaker choice will be critical, but not
impossible. 3dB steps aren't the end of the world,
anyway.

IIRC Mullard had an EL84 design that that worked with a lower load
impedance than is commonly used with EL84s, probably perfect for use
with this "Iron".


Regards,

John Byrns

[Chris Hornbeck]

On Mon, 25 Sep 2006 03:32:34 GMT, John Byrns
wrote:

IIRC Mullard had an EL84 design that that worked with a lower load
impedance than is commonly used with EL84s, probably perfect for use
with this "Iron".

I'm kinda assuming (yeah, I know) that Peter will strap G2's
to plates, as any right-thinking, God-fearing person would.(!)

The standard 7591 plate-to-plate load was 6600 Ohms, not
too far below the EL84 numbers of 8000 to 10000, but these
numbers are all for pentode or UL use, as they were
*always* used back in the day.

These OPT's don't have screen taps, so anything except
triode strapping would be pretty strange to contemporary
fashion, but not impossible.

Push-pull parallel'd EL84's would be very tasty if
available filament current allowed. Modern Russian
bottles run forever with 400 volts on the plates+G2.
Easy cathode bias; very linear, and forgiving loading, too.
Maybe 30-35 mA per bottle... Class A all the way.

Much thanks, as always,

Chris Hornbeck

[Jon Yaeger]

Omer Suleimanagich wrote:

If anything, I would like to see one of these units use 6550's or KT90's
if you could take this unit there.

That's just me!

I do have a matched quad of NOS Tung-Sol 6550s. And I think I have a
set of unmatched NOS Philips floating around somewhere. But this seems
like a lot for such small OPTs. I was saving the 6550s for the Scott
LK-150, anyway.

I do also have Mullard & GE EL34s, I had not counted on purchasing new
tubes... but I will take this under advisement as I search for
appropriate circuits. Once I do choose output tubes, I will work on the
layout, sheet-metal and spacing as I do not want a mare's nest above or
below the chassis, nor do I want heat problems. I have also been
hoarding some very nice ceramic sockets of all sizes for some years,
some of them equipped with bright nickle-plated flanges and shields
should that need arise.

Thoughts on filtering? I intend to use a bridge rectifier, I have been
thinking of using parallel 2uF, 600V mylars as setting them staggered
on both sides of a glass perf-board below the chassis would not add
much depth, not take up much real-estate relative to the tube layout
and could be neatly shielded "along the back" so to speak.

Alternately, I have a supply of 5AR4s, more 5U4s than should be
considered sane, and so forth. Also various chokes, though none of them
much more than junk-box stuff.

Thanks again for the replies. I am collecting ideas at this point. When
the cold weather sets in and the Honey-dos & such reduce, I will start
collating them to an actual starting point.




My neighbor retrofitted a Fisher 500 with EL34s and it works fine, in spite
of the fact that the EL34 draws 1.5A of filament current and the 7591 0.8A
each. Personally, I wouldn't tax the OEM filament transformer that much.

I also wouldn't sub a quad of EL84s for a pair of 7591s. Simpler is better.
Balance & matching is easier with fewer tubes.

The 7591 is a good tube and I'd probably stick with it. If you are looking
for something cheaper, the 6L6/5881 series draw 0.9 A heater current and can
operate at the voltages you'll encounter.

Fisher used solid state full-wave rectification in this series.

Good luck.

Jon

[Peter Wieck]

Jon Yaeger wrote:
Stuff snipped.

Thank you.

The OEM ran 2 x 12AX7 + 4 X 7591 from one winding and 4 x 12AX7 + 2 X
6AU6 + 1 x 6AQ8 from another, best I can read a very tiny schematic and
no further research yet.

With care, I think I have some wiggle-room as I am not running a
receiver, just a power-amp. But de-rating the total load is a good
idea.

I am definitely not trying to "cheap out", I was kinda-sorta trying to
stick within my present tube stock. Given that some of my 'vintage'
12AX7s are apparently worth more than a JJ quad of 7591s, that is not
the point. I could probably flog a pair of NIB smooth-plate teles and
make enough to cover gold-plating whatever results I achieve... Hey,
that's the ticket!! If it don't work, it looks good, and I can still
brag....

Peter Wieck
Wyncote, PA

[John Byrns]

In article ,
Chris Hornbeck wrote:

On Mon, 25 Sep 2006 03:32:34 GMT, John Byrns
wrote:

IIRC Mullard had an EL84 design that that worked with a lower load
impedance than is commonly used with EL84s, probably perfect for use
with this "Iron".

I'm kinda assuming (yeah, I know) that Peter will strap G2's
to plates, as any right-thinking, God-fearing person would.(!)

The standard 7591 plate-to-plate load was 6600 Ohms, not
too far below the EL84 numbers of 8000 to 10000, but these
numbers are all for pentode or UL use, as they were
*always* used back in the day.


The Mullard book "Mullard Tube Circuits For Audio Amplifiers" describes
what Mullard calls "Low Loading" operation of pentodes. Mullard claims
that "Low Loading" gives lower distortion than the normal loading for
the EL84. "Low Loading" uses both a lower load impedance and lower
standing current in the two tubes, in the case of the EL84 the plate to
plate load impedance is 6k Ohms, and the standing plate current is 2x24
mA. The general scheme is described on page 19 of the book, and its
application is described in the article on the 510 amplifier starting on
page 39. Three output stage options are described for the 510 using
Normal, Low, and Distributed loading.


Regards,

John Byrns

[Peter Wieck]

Bret Ludwig wrote:

I would dodge the whole issue of how much current the filaments pull
(well, heaters) by using a second, dedicated heater supply transformer.
And given the price of NOS audio types I would do my experimentation
and prototyping with the cheapest new tube, on the proven theory
accidents happen. Then you can put in your NOS glass.

Of course, and of course. Unless I go for a minimalist design (and why
I was drawn to the EL84/6BQ5 in the first place. I was figuring a total
of six or eight tubes with a SS power-supply. If I do put a tube
phono-pre-amp on the same chassis, it would have a dedicated filament
supply, likely with DC on the filaments for lower noise... just my
random thought on the noise bit related to phono stages And that would
require a volume control amongst other things.

I do not agree the 7591 is a good tube. There are IMO reasons it never
was used in successful or desireable guitar amps nor, with the
exception of the MC225, any of the big players' hi-fi gear. It is
(hint, hint!) more less a 50L6 with a 6.3 heater.

Be that as it may, that it was never used in a guitar amp is more a
positive in my mind than a negative. Guitar amps are stupid, slow,
sloppy beasts at best made for brute-force purposes, and distortion is
desireable. Now, Scott and Fisher were Big Players by any measure,
Avery Fisher Hall at Lincoln Center was built on that play... So don't
sell them so short so fast.

If your goals are to actually have a first rate amp for serious
listening as opposed to something to mess with on the bench-a good
goal, but different-have you thought of selling those Fisher
transformers to Fisher owners needing them (as there are no repros....)
or guitar guys, and buying some new hi-fi transformers?

That is a thought as well. But I am a parsimonious (NOT cheap, BTW)
SOB, I have the Fisher iron.... Yeah, I could flog them
onesies-twosies-or-a-set, then I would be responsible for them at a
level that I resist (but do not necessarily reject). On the other hand,
Magnequest, I am repeatedly told, is right down the street from me....

One thing to keep in mind: We have one last vacation trip this early
fall, and some wrapping up at the summer house. I will not be even
sketching a schematic until November at the earliest. Right now, it is
all picking up ideas and collating them for the best results. I will be
learning each step of the way, so much caution and much testing will be
done as I go along. This amp is no Athena springing fully armored from
her father's brow. To-date, I have fixed them, never designed them.
Cleaned & restored the painting, never painted it.

Peter Wieck
Wyncote, PA

[Sander deWaal]

"Peter Wieck" said:


One thing to keep in mind: We have one last vacation trip this early
fall, and some wrapping up at the summer house. I will not be even
sketching a schematic until November at the earliest. Right now, it is
all picking up ideas and collating them for the best results. I will be
learning each step of the way, so much caution and much testing will be
done as I go along. This amp is no Athena springing fully armored from
her father's brow. To-date, I have fixed them, never designed them.
Cleaned & restored the painting, never painted it.


How about a pair of 6B4G in push pull per channel?
They're fairly easy to drive, almost like a 2A3, and the filament is a
modest 6V/1A per tube.

You''l get about 10...15 watts of nice triode power, depending on the
losses in the tranny and the amount of class A operation that you
allow for.
Also, the high voltage doesn't have to be absurdly high, everything
from 320...400V will work fine, if they're indeed 6600 ohms from plate
to plate.

I have a similar amp with 2A3s and old Unitran trannies, that also
happen to be 6600 ohms (intended for PP EL34 UL).
Driven with a nice ECC83 floating paraphase and 12BH7 driver stage,
there's plenty of voltage swing available.

I can scan the schematic and e-mail it to you, if you like.

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Peter Wieck]

Sander deWaal wrote:

I can scan the schematic and e-mail it to you, if you like.

That would certainly be an elegant place to start.

I do happen to have four 2A3s in the inventory as well, but I would
_never_ use them for this purpose if/as there are vintage radios in
need.

Thank you!

Peter Wieck
Wyncote, PA

[Sander deWaal]

"Peter Wieck" said:


I can scan the schematic and e-mail it to you, if you like.


That would certainly be an elegant place to start.

I do happen to have four 2A3s in the inventory as well, but I would
_never_ use them for this purpose if/as there are vintage radios in
need.

Thank you!



FWIW, Sovtek and some Chinese manufacturers make 2A3s, and they're
excellent for audio.

I wouldn't dare to use NOS, but I know that there must be truckloads
of Ultron 6B4Gs around somewhere, at least they were made and sold
well into the '80s for just pennies.
They can't be all gone, can they?

The only problem with 6B4G as opposed to 2A3 is the higher potential
difference between one side of the filament cathode and the other,
when DC is used.
When using AC for the filament, that's not much of a problem (who said
anything about hum?) , but with DC filament supply, this may well be a
problem with 6B4G wrt. linearity.
I haven't encountered this with the 2A3s I have, which happen to be
oddball Chinese versions with octal sockets that apparently nobody
wanted, so I took them for a mere 10 euros at a local hamfest.

2A3s are still useable with AC filament supply, as long as one
carefully balances between both ends of the cathodes to ground with a
potmeter, or even better, a CT on the filament winding.

I'll have to dig into the archives for the schematic, and e-mail it as
soon as I have found it.

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Raymond Koonce]

Sander deWaal wrote:

"Peter Wieck" said:



snip


FWIW, Sovtek and some Chinese manufacturers make 2A3s, and they're
excellent for audio.

Sander and Peter,

I can second the recommendation of the Sovtek 2A3s. They're sturdy. I
had a friend who accidentially reversed a 2A3 and a 5Z3 in their
respective sockets (300-0-300 VAC power trans.) and both tubes survived
a power-on.

Regards,

Raymond

snip

[John Byrns]

In article .com, "Bret
Ludwig" wrote:

Jon Yaeger wrote:

My neighbor retrofitted a Fisher 500 with EL34s and it works fine, in spite
of the fact that the EL34 draws 1.5A of filament current and the 7591 0.8A
each. Personally, I wouldn't tax the OEM filament transformer that much.

I also wouldn't sub a quad of EL84s for a pair of 7591s. Simpler is better.
Balance & matching is easier with fewer tubes.

The 7591 is a good tube and I'd probably stick with it. If you are looking
for something cheaper, the 6L6/5881 series draw 0.9 A heater current and can
operate at the voltages you'll encounter.


I would dodge the whole issue of how much current the filaments pull
(well, heaters) by using a second, dedicated heater supply transformer.
And given the price of NOS audio types I would do my experimentation
and prototyping with the cheapest new tube, on the proven theory
accidents happen. Then you can put in your NOS glass.

I do not agree the 7591 is a good tube. There are IMO reasons it never
was used in successful or desireable guitar amps nor, with the
exception of the MC225, any of the big players' hi-fi gear. It is
(hint, hint!) more less a 50L6 with a 6.3 heater.

Bret, can you explain on what basis you say a 7591 is "more less a 50L6
with a 6.3 heater"? The 7591 and the 50L6 aren't even remotely related as
far as I can tell. The 6.3 volt heater version of the 50L6 is the 6W6.
Per the following table the 6W6 has a lower plate dissipation rating, a
lower transconductance, and a higher heater current/power requirement than
the 7591. Oh, and by the way, the 50L6/6W6 is a great tube.

6W6 7591

Plate Dissipation 12 Watts 19 Watts

Transconductance 8,000 umhos 10,200 umhos

Heater current 1.2 amps 0.8 amps


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

[Peter Wieck]

Bret Ludwig wrote:

Magnequeef is a corupt dishonest outfit, if that's who you want to
support go right ahead. I will and have bought stuf from halfway around
the world simply because I do not wish to support the son of a whore
Mike LeFevre. He is a liar, a crook and a charlatan.

Lemme see. Bret Ludwig, Andrew Jute McCoy, George Middius and various
assorted sock-puppets, slime, exudations and odiferous fulminations
dislike Magnequest.

Hmmmm..... Looks like a damned solid endorsement to me.

Peter Wieck
Wyncote, PA

[Omer Suleimanagich]

What about being unique and experimental, and make an amp using four 1625's?

Omer


"Bret Ludwig" wrote in message
ps.com...

John Byrns wrote:
snip





I do not agree the 7591 is a good tube. There are IMO reasons it never
was used in successful or desireable guitar amps nor, with the
exception of the MC225, any of the big players' hi-fi gear. It is
(hint, hint!) more less a 50L6 with a 6.3 heater.

Bret, can you explain on what basis you say a 7591 is "more less a 50L6
with a 6.3 heater"? The 7591 and the 50L6 aren't even remotely related
as
far as I can tell. The 6.3 volt heater version of the 50L6 is the 6W6.
Per the following table the 6W6 has a lower plate dissipation rating, a
lower transconductance, and a higher heater current/power requirement
than
the 7591. Oh, and by the way, the 50L6/6W6 is a great tube.

6W6 7591

Plate Dissipation 12 Watts 19 Watts

Transconductance 8,000 umhos 10,200 umhos

Heater current 1.2 amps 0.8 amps



Maybe more less than more!

The above table is only useful if you add on figures for other tubes
like the 6L6, 6V6, 6AQ5 and 6BQ5 so an overall pattern can be
established. As with the 50L6 intended for AA5 radios, the 7591 was
intended to be an improvement over the 6L6/5881 in needing less drive
and saving a stage. In the late seventies they were cheap and I
decided to experiment with building a guitar amp with one and players
"thought it blew". (They might have said some different thing, "sucks"
was common then but I don't remember "blows" as much.) It went from
clean to total powerboot ("power boot" meant "vomit violently", nothing
to do with computers, which booted with toggle switches, or organ stop
like keys, on the front panel) in a hurry.

I dislike it for hi-fi because of ruggedness and price as well as its
overload characteristics. While in the hi-fi business we like to stay
very far in the linear range, music inherently has a high crest factor
and unless you have 10 kW you will overload sooner or later.

I agree the 50L6 is a great tube...if you are into AA5 radios. I never
liked series string plastic case radios, Hammarlunds and Collinses and
Racals were more my style.

[Jon Yaeger]

in article , Bret Ludwig
at wrote on 9/26/06 8:22 PM:


John Byrns wrote:
snip





I do not agree the 7591 is a good tube. There are IMO reasons it never
was used in successful or desireable guitar amps nor, with the
exception of the MC225, any of the big players' hi-fi gear. It is
(hint, hint!) more less a 50L6 with a 6.3 heater.

Bret, can you explain on what basis you say a 7591 is "more less a 50L6
with a 6.3 heater"? The 7591 and the 50L6 aren't even remotely related as
far as I can tell. The 6.3 volt heater version of the 50L6 is the 6W6.
Per the following table the 6W6 has a lower plate dissipation rating, a
lower transconductance, and a higher heater current/power requirement than
the 7591. Oh, and by the way, the 50L6/6W6 is a great tube.

6W6 7591

Plate Dissipation 12 Watts 19 Watts

Transconductance 8,000 umhos 10,200 umhos

Heater current 1.2 amps 0.8 amps



Maybe more less than more!

The above table is only useful if you add on figures for other tubes
like the 6L6, 6V6, 6AQ5 and 6BQ5 so an overall pattern can be
established. As with the 50L6 intended for AA5 radios, the 7591 was
intended to be an improvement over the 6L6/5881 in needing less drive
and saving a stage. In the late seventies they were cheap and I
decided to experiment with building a guitar amp with one and players
"thought it blew". (They might have said some different thing, "sucks"
was common then but I don't remember "blows" as much.) It went from
clean to total powerboot ("power boot" meant "vomit violently", nothing
to do with computers, which booted with toggle switches, or organ stop
like keys, on the front panel) in a hurry.

I dislike it for hi-fi because of ruggedness and price as well as its
overload characteristics. While in the hi-fi business we like to stay
very far in the linear range, music inherently has a high crest factor
and unless you have 10 kW you will overload sooner or later.

I agree the 50L6 is a great tube...if you are into AA5 radios. I never
liked series string plastic case radios, Hammarlunds and Collinses and
Racals were more my style.



AA5 radios (at least the ones that I remember) used 50C5s, not 50L6.

What ones are you referring to that supposedly use 50L6's?

Jon

[Peter Wieck]

Jon Yaeger wrote:
AA5 radios (at least the ones that I remember) used 50C5s, not 50L6.

What ones are you referring to that supposedly use 50L6's?

http://www.nostalgiaair.org/PagesByM...5/M0003475.pdf

And many others in the Crosley line.

http://www.nostalgiaair.org/PagesByM...1/M0013591.pdf

And many others in the Philco line.

Also, Belmont, RCA, Bendix.... And so forth.

Peter Wieck
Wyncote, PA

[Peter Wieck]

Omer Suleimanagich wrote:
What about being unique and experimental, and make an amp using four 1625's?

Omer:

I would like to build this beast without a top cage. Animals and
grandchildren preclude a grid-cap. No HV above the chassis.

But, an interesting idea withall. I understand that the 1625 is a
drop-in for the 807, which has its following, and one I briefly
considered until the grid-cap came to mind.

Peter Wieck
Wyncote, PA

[Sander deWaal]

"Peter Wieck" said:


Sander deWaal wrote:

I can scan the schematic and e-mail it to you, if you like.


That would certainly be an elegant place to start.

I do happen to have four 2A3s in the inventory as well, but I would
_never_ use them for this purpose if/as there are vintage radios in
need.

Thank you!


Just a reminder: I'm halfway through my stash of loose schematics,
sketchbooks etc ;-)

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Peter Wieck]

Bret Ludwig wrote:
Peter Wieck wrote:
Omer Suleimanagich wrote:
What about being unique and experimental, and make an amp using four 1625's?

Omer:

I would like to build this beast without a top cage. Animals and
grandchildren preclude a grid-cap. No HV above the chassis.

Then you'd be right irresponsible not to put a cage on in any event.
And keep it off the floor!

Good design and layout will protect small hands from hot tubes. And
cats sense infra-red so would not be prone to being burnt. But not from
kitten paws pulling grid-caps, and the potential consequences to small
hands. Off the floor... yeah, right. Why didn't I think of that???

Peter Wieck
Wyncote, PA

[Chris Hornbeck]

On 27 Sep 2006 03:51:23 -0700, "Peter Wieck" wrote:

But, an interesting idea withall. I understand that the 1625 is a
drop-in for the 807, which has its following, and one I briefly
considered until the grid-cap came to mind.

It has a different (nowadays pretty much unique) base, 7 pins,
and the 12.6 volt filament.

Upside is that beautiful bottles made by extinct hobbits are
available for peanuts.

But don't tell anybody, or they'll disappear.

Much thanks, as always,

Chris Hornbeck

[MarkS]

"Chris Hornbeck" wrote in message
...
On 27 Sep 2006 03:51:23 -0700, "Peter Wieck" wrote:

But, an interesting idea withall. I understand that the 1625 is a
drop-in for the 807, which has its following, and one I briefly
considered until the grid-cap came to mind.

It has a different (nowadays pretty much unique) base, 7 pins,
and the 12.6 volt filament.

Upside is that beautiful bottles made by extinct hobbits are
available for peanuts.

But don't tell anybody, or they'll disappear.

Much thanks, as always,

Chris Hornbeck

The 7 pin that fits this tube is available from AES, they seem to be recent
production. Tubes are $5.50 ea! I have a few and they are built like the
baked clay **** house down the street. Thick ceramic support plates ect.
Nice tubes. They certainly would be a good match to the Fisher iron (triode
strapped or tetrode w/ regulated screens) but understand the safety
considerations due to the plate caps. I seem to remember reading that they
were used as Tx tubes in MIL hardware as installed in fighter planes?
Best Regards,
MarkS

[David L. Foreman]

On 27 Sep 2006 03:51:23 -0700, "Peter Wieck" wrote:


Omer Suleimanagich wrote:
What about being unique and experimental, and make an amp using four 1625's?

Omer:

I would like to build this beast without a top cage. Animals and
grandchildren preclude a grid-cap. No HV above the chassis.

But, an interesting idea withall. I understand that the 1625 is a
drop-in for the 807, which has its following, and one I briefly
considered until the grid-cap came to mind.

Peter Wieck
Wyncote, PA

Peter
The 1625 has a 28 volt heater and I think the suppressor was tied in some
different way. The hams building SSB linear amps would remove the base and
disconnect the suppressor, bring it out so they could connect directly to it.
The 1625 was used in the ARC-5 etc. transmittes and were very cheap, being war
surplus. They would, if I remember, use 4 of them in the amp. A lot less
expensive then the 807.
Dave Foreman