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Does anyone have specs for the "new" Tung-sol 7591s
Does anyone have specs for the "new" Tung-sol 7591s
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Old 16th November 2019, 03:24 PM   #1
charnich74 is offline charnich74  United States
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Default Does anyone have specs for the "new" Tung-sol 7591s

Hi guys, I was trying to find a spec sheet for the new version of the Tung-sol 7591s. I've heard they are a hotter tube than the originals. The only spec sheet I can find was on tubedepot and its the one for the original tube from 1961. Cheers
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Old 16th November 2019, 03:40 PM   #2
Steve Morley is offline Steve Morley  Canada
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https://shop.ehx.com/catalog/addimages/7591.pdf
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Old 16th November 2019, 04:04 PM   #3
kodabmx is offline kodabmx  Canada
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Does anyone have specs for the "new" Tung-sol 7591s
Quote:
Originally Posted by charnich74 View Post
Hi guys, I was trying to find a spec sheet for the new version of the Tung-sol 7591s. I've heard they are a hotter tube than the originals. The only spec sheet I can find was on tubedepot and its the one for the original tube from 1961. Cheers

Unfortunately, the one Steve linked is from 1961 also.

The Tung-Sol website has the datasheet, but they've just replaced the bottom line of the sheet with an overlay saying New Sensor. It's the old datasheet, too.

Tung-Sol.com:: 7581 Vacuum Tube page
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Old 16th November 2019, 04:12 PM   #4
petertub is offline petertub  Sweden
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Does anyone have specs for the "new" Tung-sol 7591s
Quote:
Originally Posted by charnich74 View Post
Hi guys, I was trying to find a spec sheet for the new version of the Tung-sol 7591s. I've heard they are a hotter tube than the originals. The only spec sheet I can find was on tubedepot and its the one for the original tube from 1961. Cheers
If it is a true 7591 that spec will do. If figures are different it is no 7591
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Old 16th November 2019, 05:04 PM   #5
charnich74 is offline charnich74  United States
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Quote:
Originally Posted by kodabmx View Post
Unfortunately, the one Steve linked is from 1961 also.

The Tung-Sol website has the datasheet, but they've just replaced the bottom line of the sheet with an overlay saying New Sensor. It's the old datasheet, too.

Tung-Sol.com:: 7581 Vacuum Tube page
Ok now I'm really confused. This is listed as a 7581 not a 7591, and why doesn't ts when list a 7591. Or more specifically a 7591A is what they are being Marketed as.

*edit* just noticed that the tube they call a 7581 has a different pinout than the 7591.

Last edited by charnich74; 16th November 2019 at 05:30 PM.
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Old 16th November 2019, 05:07 PM   #6
charnich74 is offline charnich74  United States
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Quote:
Originally Posted by petertub View Post
If it is a true 7591 that spec will do. If figures are different it is no 7591
I don't get why multiple resellers of the tube, including Jim Mcshane are telling me I'll b need to rebias the amp and the dissipations are different on the new tube when all written specs are the same. WTH is going on? On paper it looks like it is a drop in replacement.

Last edited by charnich74; 16th November 2019 at 05:18 PM.
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Old 16th November 2019, 05:17 PM   #7
petertub is offline petertub  Sweden
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Does anyone have specs for the "new" Tung-sol 7591s
Quote:
Originally Posted by charnich74 View Post
I don't get why multiple resellers of the tube, including Jim Mcshane are telling me I'll b need to rebias the amp and the dissipation temps are different on the new tube when all written specs are the same. WTH is going on? On paper it looks like it is a drop in replacement.
Tube characteristics will vary +-20% or more, and they did so even in the good old days. Thats why you have to rebias.
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Old 16th November 2019, 05:25 PM   #8
charnich74 is offline charnich74  United States
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Quote:
Originally Posted by petertub View Post
Tube characteristics will vary +-20% or more, and they did so even in the good old days. Thats why you have to rebias.
Thanks for the insight but I think there's more to it than that. Here is a snippet from McShanes website. "Important note - updated! There have been some cases where the new production 7591A (and 7868) tubes have had trouble
in circuits using a very high value grid resistor - as vintage Scotts, Fishers, and others sometimes do. The best solution is changing
all the grid resistors to 200K-220K from the original value, since often the factory spec resistors exceeded the maximum
recommendations. For instance, Fisher routinely used 330K carbon resistors that would often drift up to 360K over time! As well,
to prevent loss of deep bass energy a change of the output coupling cap value to .1 uf (preferred) is needed. I stock all the parts
you need, the parts cost is only $15.00 to $30.00 per amp, depending on the coupling cap you prefer to use. As well, many amps
will require adjustable bias to be installed to accommmodate the available tubes.
"

And here is what he said in an email to me."

I believe your amp has adjustable bias – if it doesn’t it would need to be installed. Also, the stock amp has no means to measure the bias. The easiest solution is to install 10 Ohm 1 watt resistors in each tube cathode from the cathode to ground. This will allow you to read the voltage across the resistor and use Ohm’s Law to calculate the current flow. You want no higher than 35 ma. of cathode current through any single tube – otherwise they will exceed the maximum dissipation level they can handle.

And here is what Warren Coleman said from ValueTubes "
I would count on rebiasing the amp. The new 7591s, both EH and TS, run a bit hotter than the older Sylvanias for example. To avoid having to rebias, you will want to stick to NOS or good tested used. I only have a matched quad of GE coin base 7591 available but I do see quite a few others selling good used 7591s on eBay now."

It doesn't sound to me like its spec'd the same as the old ones. All I want to see is the new dissipation values so that I can properly bias the amp.

Last edited by charnich74; 16th November 2019 at 05:39 PM.
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Old 16th November 2019, 05:45 PM   #9
petertub is offline petertub  Sweden
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Does anyone have specs for the "new" Tung-sol 7591s
It's no surprise that newly made tubes has different characteristics then old used ones.

you should always ( this is not new) check/adjust bias in fixed bias amps when changing power tubes. Even new tubes from the same brand will vary a lot, that's why using

matched tubes are important for best balance and lowest distortion.
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Old 16th November 2019, 06:26 PM   #10
6vheater is offline 6vheater
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Go to Gillespie's site.
He has an extensive tests of NOS v repro 7591 with Q & A
All your questions will be answered.

Bearing in mind a 7591 is HALF a 8417 stuffed in a 6V6 glass, and you will get why it's impossible to replicate exactly.

The problem with high gain valves like this, they self bias, and propel themselves rapidly towards melt down if not spot on.
The repro ones are made in eastern Europe, who never made /tried to make them originally.

As far as I am aware it's a Westinghouse design like the 8417 was.

Last edited by 6vheater; 16th November 2019 at 06:29 PM.
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