High Power Push Pull Amp using Type 27 Driver Tubes

[Markblom63]

I'm looking to utilize a stash of Type 27 Tubes I have and build a Higher power Push Pull design amp. I see posts all the time for lower power SET type designs but I have no use for such an amp. I would like something that actually puts out some serious power. I have 6 type 27 Tubes and want to figure out a complimenting power tube that looks similar and looks cool. So maybe a 2A3 or 300b KT66 or some other off the wall crazy power tube. So any ideas for a Amp design and or power Tubes that would go with this and be in the 1920s to 1950s Tubes. I don't want to use any small tubes.
I figured there would be some threads on this but I can't find anything all I find is things like 8 watts - 12 watts out I want more in the 35 Watt to 100 Watt Push Pull amp using vintage tubes.
So anyone have any plans for such a thing or tube ideas ?
I have built with good success a couple of Preamps and Amps using new tubes.

 

[Tjj226]

2a3 or even a 300b wont get you to the 35 watt range without doing something like a parallel push pull amp which would be a ridiculous build considering you want something to simply use up your 27 tubes.

A KT88 or KT120 pp amp would give you the power you are looking for. If you are willing to come down on the power output a bit, a single ended GM70 might work too.

 

[Markblom63]

Thanks Tjj226 The problem also it a 27 is direct heated with 2.3 volts so it limits the power transformer. my brother in law is interested in this also and has 8, 807 tubes we could try to use but not sure the power we could get with the power transformer we would have to use for the 27s it would look great but not sure we can pull it off almost would need two transformers which would be crazy. the 807 is the same as a 6l6 but has the Top connection to the plate I think it is and can handle a bit higher power
This transformer is setup for a 27 but not sure what power I would get out to a 807 tube
Transformer - Hammond, Power, 350-0-350V, 70-90 mA | Antique Electronic Supply

 

[Palustris]

The 27 is an indirectly heated triode with a filament voltage of 2.5V @ 1.75A and an amplification factor of 9. It will be challenging to use the tube either as a voltage amp with such low Mu or as a driver tube with a low Gm of only 1k umhos. Contrast that with the ubiquitous 6SN7 which has a Mu of 20 and Gm of 2600 umhos.

There is nothing unusual about having a separate filament transformer.

 

[Markblom63]

Your right I was mixed up I had just read that also. It was one of the first indirectly heated tubes. and yes I made a preamp with a separate filament transformer because the one I bought for it wasn't supplying enough current for the 5 tubes . Now just not sure I could come up with a design that would actually work to use a type 27 tube in a power amp or even in a preamp. I have read where people used them some with good success maybe it was in a preamp stage I will have to look some more

 

[Eli Duttman]

For a line stage using the #27s that has an "old time" look consider #27 voltage amplifiers working into a 6F8G section cathode followers. The triodes in the 6F8G are equivalent to those in a 6SN7. You would get the desired cosmetics, while disposing of the drive capability issue.

BTW, you could execute an all top cap signal tube Williamson power amp by employing 6F8Gs and 807s. 30+ W. is a very reasonable expectation from PP 807s.

 

[Markblom63]

Thanks Eli Not sure I exactly follow what you mean by using the 27 and the 6f8g arn't they doing the same thing the 27 just with less gain ? I do like the idea of just going with a all top cap signal using 6F8Gs and 807 probably a better amp, than I still have my 27s to try to make something out of I will have to look up what transformer would work good in that setup. the 6F8Gs look a bit expensive also was trying to use what we have on hand.

 

[Markblom63]

An externally hosted image should be here but it was not working when we last tested it.

 

[Eli Duttman]

Thanks Eli Not sure I exactly follow what you mean by using the 27 and the 6f8g
arn't they doing the same thing the 27 just with less gain ?

The #27 wired common cathode gives you a low gain voltage amplifier. OTOH, wiring a 6F8G section as a cathode follower gives you an impedance matching/current amplifying configuration that exhibits a small voltage insertion loss.