I'm fixing a Japanese receiver that uses 7591s but I don't want to spend
$100 on a set of 7591EHs.

I've got a quad of 7591XYZ. I know these are re-based 5881s. A couple of
questions:

1. What mods are required to sub in a 7591 PP circuit? I can find a
reference to the mod but not the details.

2. Any caveats?

3. Do these really suck?

TIA,

Jon

Jon Yaeger wrote:

I'm fixing a Japanese receiver that uses 7591s but I don't want to spend
$100 on a set of 7591EHs.

I've got a quad of 7591XYZ. I know these are re-based 5881s. A couple of
questions:

1. What mods are required to sub in a 7591 PP circuit? I can find a
reference to the mod but not the details.

The 7591XYZ used to come with a 10W sandbox resistor (per pair).

I think I have some in the shop somewhere, so I'll take a look
tomorrow. Something in the back of my head says the sandbox
was 200 ohms.

2. Any caveats?

Well, yeah. They sound like ass.

3. Do these really suck?

See above. ;-)

BTW, my price for a set of the 7591EH is $84. Most folks think
they sound pretty good. (I'm talking guitar amps, here.) I just
got a batch of the JJ 7591S yesterday; they're cheaper - $72/quad.
I don't know how good they are, but I've seen favorable reviews.
(Unfavorable ones, too.) They won't be ready to go for 2-3 weeks,
as I have a ****load of other (higher demand) stuff to cook before
I do those.

LV

in article , Lord Valve at
wrote on 6/4/05 1:33 AM:



Jon Yaeger wrote:

I'm fixing a Japanese receiver that uses 7591s but I don't want to spend
$100 on a set of 7591EHs.

I've got a quad of 7591XYZ. I know these are re-based 5881s. A couple of
questions:

1. What mods are required to sub in a 7591 PP circuit? I can find a
reference to the mod but not the details.

The 7591XYZ used to come with a 10W sandbox resistor (per pair).

I think I have some in the shop somewhere, so I'll take a look
tomorrow. Something in the back of my head says the sandbox
was 200 ohms.

2. Any caveats?

Well, yeah. They sound like ass.

3. Do these really suck?

See above. ;-)

BTW, my price for a set of the 7591EH is $84. Most folks think
they sound pretty good. (I'm talking guitar amps, here.) I just
got a batch of the JJ 7591S yesterday; they're cheaper - $72/quad.
I don't know how good they are, but I've seen favorable reviews.
(Unfavorable ones, too.) They won't be ready to go for 2-3 weeks,
as I have a ****load of other (higher demand) stuff to cook before
I do those.

LV



Thanks for the reply, LV.

So would you use a 200 ohm resistor for a cathode resistor in an amp with
fixed bias?

Jon Yaeger wrote:

in article , Lord Valve at
wrote on 6/4/05 1:33 AM:



Jon Yaeger wrote:

I'm fixing a Japanese receiver that uses 7591s but I don't want to spend
$100 on a set of 7591EHs.

I've got a quad of 7591XYZ. I know these are re-based 5881s. A couple of
questions:

1. What mods are required to sub in a 7591 PP circuit? I can find a
reference to the mod but not the details.

The 7591XYZ used to come with a 10W sandbox resistor (per pair).

I think I have some in the shop somewhere, so I'll take a look
tomorrow. Something in the back of my head says the sandbox
was 200 ohms.

2. Any caveats?

Well, yeah. They sound like ass.

3. Do these really suck?

See above. ;-)

BTW, my price for a set of the 7591EH is $84. Most folks think
they sound pretty good. (I'm talking guitar amps, here.) I just
got a batch of the JJ 7591S yesterday; they're cheaper - $72/quad.
I don't know how good they are, but I've seen favorable reviews.
(Unfavorable ones, too.) They won't be ready to go for 2-3 weeks,
as I have a ****load of other (higher demand) stuff to cook before
I do those.

LV


Thanks for the reply, LV.

So would you use a 200 ohm resistor for a cathode resistor in an amp with
fixed bias?

The dope sheet that comes with the 7591XYZ says you should change the cathode
resistor to 250 ohms/10 watts. (I assume this is for a pair of tubes.)

They're talking about guitar amps here. They also say if your application
is for fixed bias, you'll need to mod the bias supply so it can go into the
-37 volt region.

LV

On Fri, 03 Jun 2005 19:30:39 -0400, Jon Yaeger
wrote:

I'm fixing a Japanese receiver that uses 7591s but I don't want to spend
$100 on a set of 7591EHs.

I've got a quad of 7591XYZ. I know these are re-based 5881s. A couple of
questions:

1. What mods are required to sub in a 7591 PP circuit? I can find a
reference to the mod but not the details.

2. Any caveats?

3. Do these really suck?

TIA,

Jon

Well, sure you can rebias or use combination fixed and cathode bias.
The REAL question is - can the driver produce nearly twice as much
undistorted P-P voltage? If not, you'll be reducing output power
considerably. The amp WILL suck if you don't have enough grid drive.
JJ and EH tubes don't cost that much. Save the Sovteks for a H-K or
other amp needing 7355s - drop-in replacement.

in article 42a3435f.13401953@news-server, Tom Bavis at
wrote on 6/5/05 2:33 PM:

On Fri, 03 Jun 2005 19:30:39 -0400, Jon Yaeger
wrote:

I'm fixing a Japanese receiver that uses 7591s but I don't want to spend
$100 on a set of 7591EHs.

I've got a quad of 7591XYZ. I know these are re-based 5881s. A couple of
questions:

1. What mods are required to sub in a 7591 PP circuit? I can find a
reference to the mod but not the details.

2. Any caveats?

3. Do these really suck?

TIA,

Jon

Well, sure you can rebias or use combination fixed and cathode bias.
The REAL question is - can the driver produce nearly twice as much
undistorted P-P voltage? If not, you'll be reducing output power
considerably. The amp WILL suck if you don't have enough grid drive.
JJ and EH tubes don't cost that much. Save the Sovteks for a H-K or
other amp needing 7355s - drop-in replacement.

Thanks, Tom. I looked for a spec sheet on the 7591XYZs without much luck.
I guess I can assume they are the same as the 5881s for determining drive
requirements?


Jon Yaeger
www.yaegeeraudio.com

On Fri, 03 Jun 2005 19:30:39 +0000, Jon Yaeger wrote:

I'm fixing a Japanese receiver that uses 7591s but I don't want to spend
$100 on a set of 7591EHs.

I've got a quad of 7591XYZ. I know these are re-based 5881s. A couple of
questions:

1. What mods are required to sub in a 7591 PP circuit? I can find a
reference to the mod but not the details.

Most Japanese receivers that use 7591, use fixed bias and you'll
need to fiddle with the bias supply to use 7591XYZ.

Typically, the Japanese copied HH Scott (IIRC, Japan actually
issued an HH Scott postage stamp. Better than the New Zealanders
treated their homeboy EH Scott). The filament supply is usually
bias supply, so you may be stuck trying to bias the 7591XYZ.

JMHO, you ought to ditch the 7591XYZ on Ebay and use EH or JJ 7591.


--
Ned Carlson Triode Electronics Chicago,IL USA
www.triodeelectronics.com