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Tung Sol 7581A for more 6L6 headroom?

drbob1

Gold Supporting Member
Messages
29,207
In a cathode biased amp I suppose it's possible that you'll get an actual change in output by switching tubes, but in most fixed bias amps I don't think it makes a huge difference. Tubes with totally different construction (like substituting an EL34 or KT66 for a 6L6 may sound more different, but just beefed up tubes, not so much. You'll get way more change in clean overhead by reducing the gain of the first preamp tube by switching in a 5751, and it'll cost a lot less!
 

muchXS

Member
Messages
1,215
I can say one thing about these 7581A's, the idle current is much higher than a 6L6GC.
As mentioned above a tube will only stay clean as long as there's enough extra in the power supply to support it.

35 watts plate dissipation says to me they'll work well in certain situations, for example I'll bet they're a lot of fun in a Twin running on two tubes instead of four.

I like the GE 7591A's in my K&M Custom too...sounds great!
That's more like a beefed up 6V6 to 19W or roughly the output of a 6L6GB or lower, isn't it?
A 7591A is a whole 'nuther kettle of fish. 6V6s and 6L6s are beam power tubes. The 7591A is a power pentode, one of a very few U.S. designed power pentodes. Like other power pentodes it punches way above its weight class.
 

HotBluePlates

Member
Messages
12,059
That's more like a beefed up 6V6 to 19W or roughly the output of a 6L6GB or lower, isn't it?
19w plate dissipation like the earliest (derated) metal 6L6's. But it's in a bottle the size of a 6V6GT. And transconductance is more than double that of a 6V6 (and nearly-double a 6L6), meaning they require very little bias or drive voltage in an output stage.

Oh, and the different pinout.

The (real) 7591 is a very different tube than either a 6V6 or 6L6; I don't know how the Russian made "7591" does/doesn't live up to the old specs.
 

Greyhound69

Member
Messages
28
I have been using this tube for a few months now and I can say as someone who uses NOS tubes in most cases; this is a good tube!!! It doesn’t have the personality of the JJ 6L6GC but that’s not necessarily a bad thing. After trying both in my Kendrick badassman, this tube is more controlled and has a wider frequency response than the JJ. Of The 6l6gc types besides NOS, I would only ever use this tube or the JJ.
 

stahlhart

Silver Supporting Member
Messages
2,619
Have four of these in my V-4B, and they appear to be holding up so far, but I am keeping my fingers crossed still. Will probably take the plunge on NOS 7027As at some point. Maybe.
 

zestystrat

Member
Messages
2,616
Sorry to dig up this old thread but my '65 Tremolux is in need of some new tubes. Would this be a good choice?

In general, the Tremolux is a clean machine so the idea of more headroom isn't really a big selling point.
 

BenTobith

Fragile Harmonics
Platinum Supporting Member
Messages
1,044
Sorry to dig up this old thread but my '65 Tremolux is in need of some new tubes. Would this be a good choice?

In general, the Tremolux is a clean machine so the idea of more headroom isn't really a big selling point.
You have to be careful with these when it comes to biasing. They are rather different from regular 6L6GC/GB and could be out of the desired bias range of your amp.
 

HotBluePlates

Member
Messages
12,059
Well, 5 watts for starters.
The higher maximum rating doesn't matter.

If you compare the "new Tung Sol 7581" (35w) sheet to the "original Tung Sol 7581" sheet, you'll see New Sensor just copied the old sheet while removing dates and the original company's address.

If you then compare to the "original Tung Sol 6L6GC" (30w) sheet, you'll see the original company carried everything from the 6L6GC sheet to the 7581 sheet except for the maximum ratings.

If you then walk that back to the "original Tung Sol 6L6G" (19w) sheet, you'll see all the same data except for maximum ratings, plus one condition added to the 6L6GC sheet for 55w from a push-pull pair (due to higher supply voltage).


What's the point? 7581 = 6L6GC = 6L6G, unless the amp used exceeds the ratings of the earlier tube-type. Otherwise they "bias the same" within the limits of tube-to-tube variation (and how the individual user chooses to run the tubes).
 
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BenTobith

Fragile Harmonics
Platinum Supporting Member
Messages
1,044
The higher maximum rating doesn't matter.

If you compare the "new Tung Sol 7581" (35w) sheet to the "original Tung Sol 7581" sheet, you'll see New Sensor just copied the old sheet while removing dates and the original company's address.

If you then compare to the "original Tung Sol 6L6GC" (30w) sheet, you'll see the original company carried everything from the 6L6GC sheet to the 7581 sheet except for the maximum ratings.

If you then walk that back to the "original Tung Sol 6L6G" (19w) sheet, you'll see all the same data except for maximum ratings, plus one condition added to the 6L6GC sheet for 55w from a push-pull pair (due to higher supply voltage).


What's the point? 7581 = 6L6GC = 6L6G, unless the amp used exceeds the ratings of the earlier tube-type. Otherwise they "bias the same" within the limits of tube-to-tube variation (and how the individual user chooses to run the tubes).
I thought this thread was about the 7581A?
 

Jim Miller

Double Platinum Member
Messages
274
Last year I found a matched pair of GE 7581A slightly used that I picked up for $100. I had a very nice pair of RCA 6L6's in my Rambler, I can not totally describe the difference, but the GE's in my Rambler are just "magical". They pair very well with the natural 3d sound of a Rambler. I am just hoping that everything that I have read about the Stoutness of the GE 7581As is accurate, I can not afford the current going rate for theses tubes.

Very Respectfully,

Jim Miller
 
Messages
6,864
Same-Same.

Tung Sol 7581
Tung Sol 7581A

But really this thread is about a new Russian tube using an old American brand-name and type-number. So who really knows what the Russian tube can do?
They were met by rather heated reactions for essentially releasing a 6L6GC with people expecting a 35W bottle. Thus they went back to the drawing board and came up with the 7581A. Not tried it personally but it's supposed to have that extra amount of power that makes it an A. Also the innards are vastly different between the non-A and the A.
 






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