Oddball Compactron tube/compatability question

Pete McAvity · From: St. Louis, Missouri USA

Hoping someone can help me identify a mystery 12 pin Compactron tube. Pictured on the left is the unknown subject in a small glass envelope. On the right is a presumed stock 6C10 out of a 1972 Peavey “Vintage 410” combo for size reference. The original 6c10 tubes test strong on an old Knight 400a tester but are microphonic. So, hoping for help:

-Identifying the unknown tube to determine if it’s a suitable sub, and if unsuccessful:

-understanding any potential unwanted ramifications by blindly swapping an unknown preamp tube. Since these are each essentially one and a half 12au/t/x’s in a bottle, can they be safely exchanged with no bad results to the amp aside from the signal quality?

Thanks, all.

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Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.

They say "thats how it goes". I say "that ain't the way it stays!"

Bruce Derr · From: Lee, New Hampshire, USA

There are around 100 different compactron tube types and only a few of them are triple triodes. Chances of the unmarked tube being compatible are small. It's not a good idea to try it in the amp without knowing the tube type or at least the pinout. It's possible to cause damage to the amp.

Stephen Cowell · From: Round Rock, Texas, USA

If you can plug it into your tube tester with the same socket/settings and get readings for both A and B sides then it is probably safe to plug it into your amp... there appear to be no shorts.
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Pete McAvity · From: St. Louis, Missouri USA

Thanks Stephen! Yeah, I have two & they test strong as 6c10s. I suspect that they may be 6k11 pulled from my Ampeg V4.
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.

They say "thats how it goes". I say "that ain't the way it stays!"

Donny Hinson · From: Glen Burnie, Md. U.S.A.

The 6BK11 is the best substitute for the 6C10, but they’re also scarce as hen’s teeth. A 6D10 will work, but will reduce your output, since the gain of that tube is about 35% lower. The same is true for the 6AK10. Triple triodes are rare, and the only reason Fender used them was probably because they got a good deal on a few thousand of them.

The last 6C10 I bought was back in the 1980’s, and was about $6. If you can even find a new one now, it’ll set you back from $75-$125. And if my Fender Super Twin ever needs another one, I’ll probably mod the amp chassis and install two 12AX7A’s instead, which I have a bunch of NOS in my stash.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

6C10 are not particularly rare - there is no essential problem finding one. Prices vary, but they're not insane, considering the general cost trends for NOS tubes. But quite a number of Super Champ users have subbed the less-expensive 6AC10 with reasonable results. They are both triple high-mu triode Compactrons. I think the 6C10 triodes are nominal gain = 100, 6AC10 nominal gain = 62, i.e., more or less 12AX7 vs. 5751. I frequently sub 5751 tubes in 12AX7 stages because I frequently prefer the sound. Only way I can tell is to try the sub and listen to see if I like it.

6BK11 on the other hand is essentially unobtainium. I think I may have scarfed up the last two on Planet Earth about 10 years ago at a guitar show in Cleveland, for my Ampegs. They were pulls from Ampegs - they still had the Ampeg logo on them. I don't think I've seen a true NOS 6BK11 in the last 35 years.

If your application can handle lower gains, the 6U10 is fairly abundant and inexpensive.

IMO, Compactrons were one of the dumbest ideas in the world of vacuum tubes. They were mostly marketed to TV manufacturers, with the selling point of reducing size/cost. But going away from prevailing standards is a perfect recipe for high cost. Nobody has made them for decades - why would they?

ajm · From: Los Angeles

To add to/clarify something that Dave Mudgett said:

I believe the "Super Champ" that he referred to is the late 80's Fender Super Champ designed by Paul Rivera.
I have one and it does use a 6C10.
The first and very early 70's Peavey Classic series also used them.

I agree with the comment about NOT swapping tubes willy-nilly into an amp unless you know what you are doing.
If you want to do it with your own amp, fine.
But don't advise somebody else to do it to their amp.

Pete McAvity · From: St. Louis, Missouri USA

Thanks, AJM. This is indeed a pre-Classic line Peavey, all tube. Plopped them in and they're an improvement over the pair of 6AC10s I had in (to my ears anyway)!
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.

They say "thats how it goes". I say "that ain't the way it stays!"

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Dave, I found a source for NOS 6BK11, and they have multiples available. But at $160 apiece, I don’t think there’ll be many takers! Laughing

The cheaper 6C10 is what I’d use to sub for the 6BK11. If the medium-mu amp section proved objectionable, you could tweak the B+ down on that triode plate to lower the gain. I’m not a real stickler for “original”, especially if it works the same, but I know gearheads and collectors might not go for that.

Pete McAvity · From: St. Louis, Missouri USA

Thanks Stephen! Yeah, I have two & they test strong as 6c10s. I suspect that they may be 6k11 pulled from my Ampeg V4.
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.

They say "thats how it goes". I say "that ain't the way it stays!"

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