Author Topic: GE 7581a tube anyone?  (Read 675 times)

Offline Kent Kassler

GE 7581a tube anyone?
« on: June 19, 2018, 07:24:41 AM »
Morning gents...i am rebuilding a pair of Quad ii amps and have three of these output tubes....anybody perhaps have a single to sell maybe?
Cheers Andre.
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.

Offline fredeb

Re: GE 7581a tube anyone?
« Reply #1 on: June 19, 2018, 07:33:51 AM »
Hey Andre - I think I have a single 7581 , not sure whether it is a GE though ?


« Last Edit: June 19, 2018, 07:50:56 AM by fredeb »
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline fredeb

Re: GE 7581a tube anyone?
« Reply #2 on: June 19, 2018, 08:10:48 AM »
Just looked - it appears that what I have is a pair of EH 7591a's . Which in fact looks suspiciously like a Ruskie 6P3S-E , or like tube depot's "Prefered Series" 6L6-GC .



 





...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Kent Kassler

Re: GE 7581a tube anyone?
« Reply #3 on: June 19, 2018, 08:15:41 AM »
Howzit bud....looks like I will have to get a quad of 6L6 or such for this pair if I don't find one....so sad....they were garage packed and one was smashed.....a real pity.....I should see Rick soon and will send your goodies to the West with him....anyone have a quadset of tubes as an option then for these.....have lots to trade or buy.
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.

Offline Kent Kassler

Re: GE 7581a tube anyone?
« Reply #4 on: June 19, 2018, 08:20:10 AM »
Maybe when you have a gap....Will send some pics of the last pair I did....I can't post pics....lame i know....but they come out really nice.....should post them here.
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.

Offline fredeb

Re: GE 7581a tube anyone?
« Reply #5 on: June 19, 2018, 11:36:55 AM »


Andre has 3 of these ATM .

« Last Edit: June 19, 2018, 11:40:41 AM by fredeb »
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Qualityten

Re: GE 7581a tube anyone?
« Reply #6 on: June 24, 2018, 04:40:38 PM »
The EH 7591A tubes were re-pinned 6L6/5881 tubes.  That was the only new option till JJ started making true 7591s.

Offline Ampdog

Re: GE 7581a tube anyone?
« Reply #7 on: June 29, 2018, 12:14:30 PM »
Before some confusion sets in:

Types 7581A, 7027 and 6L6GC are direct equivalents for all practical purposes, except that the 6L6GC Pa = 30W compared to the other's 35W. There are some differences in maximum voltages. The 7581 'specially made for audio', cannot now find any reason e.g. more ruggedised as I seem to recall  from a descrioption ca. 1960. They are all beam tetrodes.

Type 6(Pi)3S is also about the same, but with lower Pa = 19W, thus about the same as the first 6L6s - lower than 5881 (little data obtainable).  Also a beam tetrode.

Type 7591 is quite different. It is a power pentode (not beam tube) quite similar to the EL34, but with Pa=19W maximum only, heater current 0,8A. (Not sure that it fits anywhere in this thread topic.)
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Nidri

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Re: GE 7581a tube anyone?
« Reply #8 on: June 29, 2018, 08:36:40 PM »
I know it's expensive but would it not be worthwhile braving the 'Bay to get a fourth GE to complete the quad set?
e.g. https://www.ebay.com/itm/One-pair-of-7581A-Tubes-From-GE-Close-Ratings-Different-Getter-Shape/371430926600?hash=item567b022908:g:wk0AAOSwDNdV6vdn

Otherwise (heresy!) I've read good things about the new production Tung-Sol 7581A
(There was an earlier 7581 - supposedly the newer A model is much improved.)
https://www.tubedepot.com/products/tung-sol-7581a-new-production-power-vacuum-tube

If the Rand wasn't so weak these semi-NOS Winged C's are also really, really good (I only have a pair unfortunately).
https://www.watfordvalves.com/product_detail.asp?id=273

Or take a chance on some cheap NOS Sovteks?
https://nesstone.com/product/sovtek-5881-6l6gc-nos-tube/

OR some NOS Philipses:
https://www.ebay.com/itm/JAN-Philips-6L6WGB-tube-NOS-matched-quad/292610567088?hash=item4420f2ebb0:g:u2gAAOSw-b9az6TH


2c
« Last Edit: June 29, 2018, 08:45:04 PM by Nidri »

Offline Ampdog

Re: GE 7581a tube anyone?
« Reply #9 on: June 30, 2018, 04:02:38 AM »
OOPS!

The mire deepens/thickens. Because the basic 6L6 construction was so successful (almost like the DC3- Dakota aircraft!) a number of variations sprang up over the years.

Some good, some not so good.

Mind that the 6L6WGB has 26W maximum plate dissipation and somewhat lower rated maximum electrode voltages. But again being a military intended valve, many users have claimed using higher voltages and going to 30W plate dissipation. The difference can be negligible in practice; dependant on ventilation.

As said, because of the highly successful design one needs to be careful of manufacturer's claims. Not intending to upset members unneccesarily, but when I read about bass, mids and treble being superior this or that way, I disregard claims. (A different topic: Electronic devices do not have emotion and cannot produce this or that tone more lushly or whatever the claim. But let that rest.)

Thus in the almost frenetic scramble to impress, I would direct members away from brand promotion. I would encourage reads from a.o. the international "DIYaudio" site. Stalwarts like Tubelab, Wavebourn, SY, Kevin KR et al can be believed. A lot of reading available, but mind the potholes!

If of any value, I found the more expensive Tung-Sol 6L6GC - STR to have a quite small spread in characteristics; my tests involved some 30 tubes, so perhaps of some value. (I currently use them in the Hallé, if of further interest, but where they have not yet had a lot of hours.) Another visible feature: The cooling fins (or one U-shaped one) on the G1 pins up top. E.g. GEC sports the largest ones. A most reliable 6L6GC; I imported 12 about 30 years ago but all gone by now.

Perhaps of little importance in docile domestic equipment, but the comparatively flimsy element mounting structure in some photos does not impress. These days where internal connections go directly to tube pins, those act as mechanical 'braces', and there is little excuse not to have a sturdy internal mounting construction.

Last general point: Anodes which have a slight arc shape of the active part is superior to fully box shaped ones.

This all about the 6L6, but as said the 7581A is identical except for slightly higher maximum ratings, at least according to the RCA Tube Manual and other data sheets.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline charles

Re: GE 7581a tube anyone?
« Reply #10 on: June 30, 2018, 07:40:24 AM »
Ampdog, you are correct regarding the 26W maximum plate dissipation. I found the 5881's data in one of the RCA's Receiving Manuals.

The 5881 exact equivalent is 6L6WGB

Quad II's operators manual indicates the 5881/6L6G as replacements for the KT66

I still have 6L6WGB/5881 NOS valves in stock.             

Offline Nidri

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Re: GE 7581a tube anyone?
« Reply #11 on: June 30, 2018, 07:46:13 AM »
^^^ Thank you for the further insight.

I suppose valves are like any other product category; manufacturers make all kinds of claims regarding their products.
Whether these claims are a) substantiated, b) meaningful or even c) true is another matter entirely.

For the Winged C valves I mentioned, for example, the manufacturer claims:
- "The Svetlana 6L6GC was designed based on the famous Sylvania STR 387 6L6GC and manufactured in the JSC Svetlana factory in St. Petersburg, Russia." (Note: Point they're making here is these weren't made by New Sensor. Further reading below*.)
- "Tight manufacturing specification, tolerances and improved processing provided the best made modern 6L6GC with improved reliability and superior sonic performance that rivalled the old USA made valves."
- "The Svetlana 6L6GC features thick mica spacers and internal bracing to help reduce vibrations and microphonics. It features a gold plated molybdenum alloy control grid and graphite coated screen grid to reduce secondary emission."

So are these claims a) substantiated, b) meaningful and c) true?

I don't know. I can't confirm their claims on any technical level, I wouldn't know what to look or test for.
(Not that I even have anything in the way of measuring equipment anyway.)
They certainly seem very rugged, for what it's worth, which I magine isn't a whole lot.

All I know is the amplifier successfully plays music when they are in position.
I'll even go as far as saying the system sounds good overall.
Which, I suppose, really just means the valves are (choosing words carefully) functioning as expected in a way that is technically compatible with the circuit they're being used in.
Whether another brand of (compatible) valve would sound any better (or worse) is, of course, a can of worms that I do not intend to open.

Well not on a public forum anyway.  ;)


* https://www.stereophile.com/news/022304svetlana/index.html

Offline Qualityten

Re: GE 7581a tube anyone?
« Reply #12 on: June 30, 2018, 11:35:00 AM »
Regarding Ampdog's points about 7591A valves.  The point I made in an earlier post about them is that although it is a 6L6 in operating conditions, the pins have been named changed to correspond to this of a 7591. I.e. It was offered as a rough plug-in replacement for 7591s when no new ones were being made.

This means that if 7591As are used as 6L6s, sockets must be required accordingly, with changes to the connections to pins 5, 6 and 8.

I hope that's helpful. I know the discussion is about 7581 and 6L6 valves. Just picking up on fredeb's post and pictures in #3 above.

Offline charles

Re: GE 7581a tube anyone?
« Reply #13 on: June 30, 2018, 12:28:22 PM »
From Ampdog:

"Type 7591 is quite different. It is a power pentode (not beam tube) quite similar to the EL34, but with Pa=19W maximum only, heater current 0,8A."

So this is not one of the 6L6 family of tubes.

I will not use it in a Quad II power amplifier. 
« Last Edit: June 30, 2018, 12:32:46 PM by charles »

Offline Qualityten

Re: GE 7581a tube anyone?
« Reply #14 on: June 30, 2018, 10:55:08 PM »
From Ampdog:

"Type 7591 is quite different. It is a power pentode (not beam tube) quite similar to the EL34, but with Pa=19W maximum only, heater current 0,8A."

So this is not one of the 6L6 family of tubes.

I will not use it in a Quad II power amplifier.
Yes, correct.  My point is don't use the 7591As either as direct 6L6 substitutes, even though they look like 6L6/5881s, as the pins are different.  Over and out. :)