6GM5 = 7591 ?????????

susan horn

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Sep 11, 1998, 3:00:00 AM9/11/98

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Hello,

Can anyone give advice reguarding the replacement of 7591s with
6GM5s??
Is there any short commings to be considered in this swap for a Fisher
500C ie.sonics ,longgevity ?
I can pick these up for less than half the price of 7591s.

Thanks
John

Ross Lipman

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Sep 11, 1998, 3:00:00 AM9/11/98

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Same tube- different pin out. You need either an adaptor ($15 ea from
AES) or rewire the sockets.

Good Luck,

Ross Lipman

rl1...@ix.netcom.com

Mr. James C. Mcshane

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Sep 12, 1998, 3:00:00 AM9/12/98

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6GM5s are equivalent to 7591 and 7868, just on a miniature 9 pin base.
to use them in an amp designed for 7591s you'll have to replace the
tube sockets or get an adapter. AES has adapters for sale.

Some receivers have very little room around the output tubes , so the
height of an adapter is a problem. I'm not aware of any difference
sonically or lifewise.

Jim McShane
MLJ...@prodigy.com

Steve Kelsay

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Sep 13, 1998, 3:00:00 AM9/13/98

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Jim Cross

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Sep 14, 1998, 3:00:00 AM9/14/98

to susan horn

susan horn wrote:
>
> Hello,
>
> Can anyone give advice reguarding the replacement of 7591s with
> 6GM5s??
> Is there any short commings to be considered in this swap for a Fisher
> 500C ie.sonics ,longgevity ?
> I can pick these up for less than half the price of 7591s.
>
> Thanks
> John

These are electrically identical with different bases. Check out the
first "tube tidbit" on the website listed below.

--
Jim Cross - Vacuum Tubes, Inc.
http://www.cinternet.net/~vactubes
email to vact...@cinternet.net
Check us out for new, used, audio, antique, and collectable types.

Vacuum Tubes, Inc.
3246 Floridale Lane
Cincinnati, OH 45239-6203

Mark Williams

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Oct 22, 1998, 3:00:00 AM10/22/98

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Sam wrote:

{OOPS, blank post -- nothing there, Sam.}

But, it's something I've wondered about. Since the 7591 is expensive,
why not sub a more common tube? However, despite Ned's suggestion, the
5881=6L6 is not a pentode, it is a beam power tube with lower plate
resistance (poorer match to output transformer, higher distortion).
It's not a perfect cross for the 7591, by any stretch.

I might try an EL-34 instead -- it is a true pentode with similar plate
resistance. Problem is the heater current is twice the current of the
7591 (1.6 A vs 0.8). Clearly that would have to be taken care of or you
risk the filament winding. The 6L6 at 0.9A is pretty safe.

I'll play it again for Sam: Has anyone tried this? Inquiring minds
inquire.

Paul Gustafson

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Oct 23, 1998, 3:00:00 AM10/23/98

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Hi Mark and R.A.T.,
How about 7868's. They are a great sounding tube with similar ratings.
There was some discussion about this a while back (during the andre
days) and they seem to be available still.
$0.02
Paul G.

Ned Carlson

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Oct 24, 1998, 3:00:00 AM10/24/98

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On Thu, 22 Oct 1998 16:10:42 -0700, Mark Williams <ma...@cup.hp.com>
wrote:

>Sam wrote:
>
>{OOPS, blank post -- nothing there, Sam.}
>
>But, it's something I've wondered about. Since the 7591 is expensive,
>why not sub a more common tube? However, despite Ned's suggestion, the
>5881=6L6 is not a pentode, it is a beam power tube with lower plate
>resistance (poorer match to output transformer, higher distortion).
>It's not a perfect cross for the 7591, by any stretch.

It's a fairly good match to the output xfmrs (usually about 6000-7000
ohms) used with 7591. Note that plate load figures aren't written
in stone by any means, figures are given for an average tube,
at the best combination of distortion & power output.

Whether 7591 is a pentode or tetrode depends on
which book you're reading GE calls it a "beam power tube",
ie: a tetrode, RCA calls it a "power pentode".
I guess I'll have to break a dud open & see.

>
>I might try an EL-34 instead -- it is a true pentode with similar plate
>resistance. Problem is the heater current is twice the current of the
>7591 (1.6 A vs 0.8). Clearly that would have to be taken care of or you
>risk the filament winding. The 6L6 at 0.9A is pretty safe.

Most of these amps are running hotter than the dickens
just the way they are.I wouldn't chance the EL34's.

I have heard of folks actually subbing 25L6 or 6W6-GT!
Don't know how well *that* works.

Ned Carlson Triode Electronics "where da tubes are!"
2225 W Roscoe Chicago, IL, 60618 USA
ph 773-871-7459 fax 773-871-7938
12:30 to 8 PM CT, (1830-0200 UTC) 12:30-5 Sat, Closed Wed & Sun
http://www.triodeel.com
Your Start Page for Tube and Tube Amp info on the net...
http://www.triodeel.com/tlinks.htm

Michael C. Marx

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Oct 25, 1998, 2:00:00 AM10/25/98

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I have used 6GM5's in my Scott 299C for almost a year. They work great.
They should. They have EXACTLY the same specs as the 7591. You really
don't gain much by using 7868's. They're rare and expensive, too.

Mike
SND Tube Sales
http://www.vacuumtubes.com