Single tube, Single ended, 20W, impossible?

[dannydanger]

Ok, going way out on a limb here perhaps but, is there a valve in existence, a large transmitting tube perhaps, that is capable of producing 15-20W in a single ended design, with no driver? I imagine it being some super high voltage monster, is there a valve that could do it or is it a pipe dream?

[leadbelly]

Why is not requiring a driver important? You're talking about high voltage, high heating power, large and expensive OPT. Having to build the driver stage is the easiest part!

[DF96]

Assuming you are starting from a 2V CD/DAC output then you will either need very high gm or a high impedance step-up transformer. I think the answer is no, and it seems a pointless thing to do anyway.

[aardvarkash10]

why? What is the rationale for such an exercise? Cheaper? No. Easier to build? No. Sonically superior? Highly unlikely.

Kinda just leaves "because I want to" I guess...

[dannydanger]

Just a hypothetical really, curious if it could be done, not if it was practical.

[tubelab.com]

I'm going out on a limb and saying no. To get 20 watts from a single tube you are going to need a bunch of transconductance, that rules out most big transmitting tubes. You are going to need at least 40 watts of plate dissipation, probably more like 60+. That rules out most small high transconductance tubes.

I can crank just over 40 watts out of a single 845 and about 38 watts out of a 211. Either of these need about 1000 volts of B+ and hundreds of volts of drive. Not available from most CD players.

The E130L is a 27 watt tube with a transconductance of 27000. It will crank out about 15 watts in pentode mode. You still need about 15 volts P-P of drive to get there without any feedback. Still not quite driverless.

The last resort? The 6HV5A and relatives. Transconductance is 65000, Mu is 300, plate dissipation is 35 watts. The plate is big enough to eat a bit more than 35 watts. So. it's a done deal, right? Not so easy. The tube needs a bunch of voltage, and it's plate resistance is real high, so feedback is almost mandantory. I have experimented a bit with this tube and have yet to tame it. Good luck!

[dannydanger]

I thought about a 100TH, but again, would need a decent driver and huge voltage supply.


Yeah, it sounds like a lot more trouble than it's worth even if it was possible. I guess it was just appealing because it hasn't been done before.

[Merlinb]

Is there a reason nobody has said KT88? (Ok, it might not QUITE manage 20W, but it could get pretty close, especially in UL)

EDIT: Oh right, with no driver tube, um...

[Arnulf]

Originally Posted by dannydanger

Yeah, it sounds like a lot more trouble than it's worth even if it was possible. I guess it was just appealing because it hasn't been done before.

Since pretty much that could be done with tubes has been done ... decades ago, one must wonder why what you're after hasn't been successfully implemented. Could it be because it is unfeasable ?

[Ty_Bower]

On a related note, what is the highest wattage spud you've seen? The original post title said "single tube", so I'll say it counts even if that tube has a triode and a pentode all in one bottle. Are there any really big compactrons out there? I found the 6MY8 (and 16MY8, 21MY8) that claims 16 watts dissipation on the pentode section. How many audio watts can you squeeze out of that?