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What tubes for a OTL tube amp?

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Tubelab_com

Tubelab_com

Member
Joined 2005
tubelab.com
twin carbon triodes bigger version than 6336. (forgot the name, its like 7000 something)
Click to expand...

There are two, the 7241 has a Mu of 2.7 with a Gm of 40,000 and the 7242 has a Mu of 9 with a Gm of 111,000 !

Both have plate currents of about 1 amp, and plate dissipation ratings of 100 watts. They actually have three cathode / grid structures wired in parallel feeding a single large carbon plate. They do fit the same socket as an 813.

I have never seen any of these and the sale prices for used ones are stupid high, like $200 each.

I have a 30 pound box of 6080's, maybe some day I'll wire a bunch of them together.
 
Tubelab_com

Tubelab_com

Member
Joined 2005
tubelab.com
$1000 7242 tube or $3 Mosfet, your choice.
Click to expand...

....I choose "none of the above"

I have been collecting and saving these for a possible OTL some day. On the left are Mil spec 6080WA's. I have probably 40 or 50 used tubes in good condition. I have another 50 or so NOS 6080, 6080WA or 6080WB tubes in the original boxes, but not all are Mil spec.

On the right are some rather used and somewhat corroded 6336A's. The ones that I have tried were good, but they were the nicer looking examples. I have more somewhere, but I'm not sure how many.

Then there's this. It's a Bendix 6080W with graphite plates. I found this at a hamfest a dozen years ago, and haven't seen another one since.
 

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koldby

koldby

Member
Joined 2003
hpeter said:
....6s33s are not very stable specimen (batch dependant), thats why you need pick good ones which do not "move around".
sometimes are seen on ebay twin carbon triodes bigger version than 6336. (forgot the name, its like 7000 something)
basically a 813like big socket, no octal here.
Click to expand...
In my experience, the 6c33 (or 6s33 if you will) are not nearly as bad as their reputation, except for their heat production, which is very real and must be dealt with. I have NOT matched the 6c33 in my amp, and it is still working fine. But, I think it is a lot easier to make an OTL circlotron with 6sa7/6080.
 
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