7591 tubes

cspyon

cspyon

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As you know, 7591 tubes were popular output tubes for McIntosh MC225, MA230, and other famous amp brands such as Eico and Fisher. I'm surprised to know that Westinghouse produced coin-base 7591 tubes, or 7591A. What surprised me more was that GE's coin-base 7591 had similar dot patterns on the glass. As you know, Westinghouse first developed and produced 7591 in 1959, but stopped producing it several years later.
Is it possible GE made 7591 for Westinghouse? 20230430_231121.jpg Screenshot_20230430-231216_eBay.jpg
 
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cspyon said:
I'm surprised to know that Westinghouse produced coin-base 7591 tubes, or 7591A. What surprised me more was that GE's coin-base 7591 had similar dot patterns on the glass.
As you know, Westinghouse first developed and produced 7591 in 1959, but stopped producing it several years later.
Is it possible GE made 7591 for Westinghouse? View attachment 2874990 View attachment 2874991
Click to expand...

From what I have read, Westinghouse 7591 production stopped in 1970 and was labeled as 7591.
They continued to market 7591's after 1970, and most of post 1970 Westinghouse 7591's that I have seen were 7591A's that were been made by Sylvania.
The Sylvania made tubes of that era are easy to identify by their "dish" style getters as opposed to the Westinghouse or GE "Halo getters".
Both GE and Sylvania made Coin Base 7591A's.
The "Halo" getters and Stencil tube ID script indicate the tubes in your pictures were made by GE.
From my experience, either GE or Sylvania 7591A's are excellent performing tubes.

From what I have read, the 7591A designation was created by Sylvania in response to Amplifier manufacturer requests for tubes that radiated less heat out of the top of the tube. The heat radiation was creating warranty issues due to heat discoloration at the top side of low profile tube enclosures..
The "dish getter" was a change to direct the heat side ways.
Since the electrical specs were identical to the 7591, other tube manufacturers adopted the 7591A designation to identify their new production 7591's without changing the direction of heat radiation.
 
Pablodeux said:
From what I have read, Westinghouse 7591 production stopped in 1970 and was labeled as 7591.
They continued to market 7591's after 1970, and most of post 1970 Westinghouse 7591's that I have seen were 7591A's that were been made by Sylvania.
The Sylvania made tubes of that era are easy to identify by their "dish" style getters as opposed to the Westinghouse or GE "Halo getters".
Both GE and Sylvania made Coin Base 7591A's.
The "Halo" getters and Stencil tube ID script indicate the tubes in your pictures were made by GE.
From my experience, either GE or Sylvania 7591A's are excellent performing tubes.

From what I have read, the 7591A designation was created by Sylvania in response to Amplifier manufacturer requests for tubes that radiated less heat out of the top of the tube. The heat radiation was creating warranty issues due to heat discoloration at the top side of low profile tube enclosures..
The "dish getter" was a change to direct the heat side ways.
Since the electrical specs were identical to the 7591, other tube manufacturers adopted the 7591A designation to identify their new production 7591's without changing the direction of heat radiation.
Click to expand...
Thanks for your kind reply.
On googling on this tube, I've found the attached document on 7591A, published by Westinghouse on April, 1963.
It mentions 7591A as early as 1963, and the so-called ''special low-loss base', which seems to refer to the coin-base tube:
chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/http://www.r-type.org/pdfs/7591a.pdf
Also, this interesting story on 7591 tubes:
https://mail.google.com/mail/u/0/#i...jsMgBNXLpjXWHfG?projector=1&messagePartId=0.1
 
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cspyon said:
Thanks for your kind reply.
On googling on this tube, I've found the attached document on 7591A, published by Westinghouse on April, 1963.
It mentions 7591A as early as 1963, and the so-called ''special low-loss base', which seems to refer to the coin-base tube:
chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/http://www.r-type.org/pdfs/7591a.pdf
Also, this interesting story on 7591 tubes:
https://mail.google.com/mail/u/0/#i...jsMgBNXLpjXWHfG?projector=1&messagePartId=0.1
Click to expand...

I believe that all coin base are not low-loss types.

The low-loss base are the micanol ones. I'm not sure, but I know GE made these tan colored base output tubes, 7591A being one of them. They maybe micanol or some other special low-loss type.

As far as I know, Westinghouse only made Bakelite bases. No micanol ones.

7591A_tan and black.jpg
 
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Mr Boochie said:
I believe that all coin base are not low-loss types.

The low-loss base are the micanol ones. I'm not sure, but I know GE made these pink colored base tubes, 7591A being one of them. They maybe micanol or some other special low-loss type.

As far as I know, Westinghouse only made Bakelite bases. No micanol ones.

View attachment 2875144
Click to expand...

That's why I started this thread.
I found one on this forum:
https://audiokarma.org/forums/index.php?threads/westinghouse-7591-date-code.398868/page-2
 
cspyon said:
Thanks for your kind reply.
On googling on this tube, I've found the attached document on 7591A, published by Westinghouse on April, 1963.
It mentions 7591A as early as 1963, and the so-called ''special low-loss base', which seems to refer to the coin-base tube:
chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/http://www.r-type.org/pdfs/7591a.pdf
Also, this interesting story on 7591 tubes:
https://mail.google.com/mail/u/0/#i...jsMgBNXLpjXWHfG?projector=1&messagePartId=0.1
Click to expand...

That Westinghouse data sheet from 1963 is interesting.
I'm not sure I understand the significance of the "controlled zero bias plate and screen currents" is, but that and the "low loss base" seem to be identified as what distinguishes it from their 7591.
As Mr Boochie points out this would indicate a Micanol base was used.
The figures of the 7591A in the data sheet show a conventionally shaped base as opposed to a coin base.
The Sylvania 7591A Tube Manual doesn't spell out base material or Zero bias plate and screen current.

The early versions of the Westinghouse 7591 had a conventional Bakelite base that was taller than the Micanol based tubes, and also had a second side getter in addition to the top getter.
There are some good pictures of the Westinghouse 7591A that accompany tubes that are currently for sale on ebay.

I couldn't access the Google link you provided for the 7591, since it required Google with personally identifiable information that I won't supply.
I think it may capture the VTV issue 20 story which I have found to be good reading.
 
See if you can access this link:

https://worldradiohistory.com/Archi...m-Tube-Valley/Vacuum-Tube-Valley-Issue-20.pdf

I don't know what the significance of controlled zero-bias plate and screen current are. I presume that it is good? :idea:

The base of the early 7591A is made of "Plaskon," low-loss material, according to Ludwell Sibley. Those are the smoother tan colored bases, on the left. The right ones are standard Bakelite.

7591A pink and black bottom1.jpg
 
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By Low Loss, do they mean it doesn't transfer heat as quickly or cost them as much to make? :rolleyes:

And thanks, Mr. Boochie, for that link, it's very interesting for historical, manufacturing, and circuitry details.
 
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probably supposed to mean less electrically leaky. I've seen some of the black base tubes where the base is absolutely barbecued to the point where I'd wonder if it was leaking electrically.
 
oldflame said:
By Low Loss, do they mean it doesn't transfer heat as quickly or cost them as much to make?
Click to expand...

"Y" = better, longer lasting electrical insulator than the typical Bakelite base. Not as good as the mil spec ceramic, but cheaper. Most "Y" tubes are mil spec.

My understanding is that GE patented "Plaskon" was longer lasting than the Bakelite base. But, not the electrical insulation that the phenolic base has (at least those built to mil spec standards).

But, it was more expensive to make, GE only used them on tubes for a few years. Mostly output tubes. They have a cult following --- along with many other things in life. :)

7581A.jpg
GE (Owensboro, KY made) 7581A
 
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I lived in Elmira NY. The Bendix tube factory became Westinghouse, or visa-versa. The cartons will note Elmira if made there.
 
Pablodeux said:
From what I have read, Westinghouse 7591 production stopped in 1970 and was labeled as 7591.
They continued to market 7591's after 1970, and most of post 1970 Westinghouse 7591's that I have seen were 7591A's that were been made by Sylvania.
The Sylvania made tubes of that era are easy to identify by their "dish" style getters as opposed to the Westinghouse or GE "Halo getters".
Both GE and Sylvania made Coin Base 7591A's.
The "Halo" getters and Stencil tube ID script indicate the tubes in your pictures were made by GE.
From my experience, either GE or Sylvania 7591A's are excellent performing tubes.

From what I have read, the 7591A designation was created by Sylvania in response to Amplifier manufacturer requests for tubes that radiated less heat out of the top of the tube. The heat radiation was creating warranty issues due to heat discoloration at the top side of low profile tube enclosures..
The "dish getter" was a change to direct the heat side ways.
Since the electrical specs were identical to the 7591, other tube manufacturers adopted the 7591A designation to identify their new production 7591's without changing the direction of heat radiation.
Click to expand...
Obviously, Westinghouse made 7591A in 1970.GridArt_20230807_155829246.jpg
And this document attests to the fact:
chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/http://www.r-type.org/pdfs/7591a.pdf
 
cspyon said:
I have no idea, but I see the Westinghouse logo on the coin-base 7591A. I wonder if Westinghouse produced both coin-base 7591A and it's original style 7591 even in the 1970s.
Click to expand...
Really? I was told those coin base Westinghouse 7591A were relabeled Sylvania (or Philips ECG) made tubes. :idea:
 
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