What would I do if I move to a much larger room and the power of Milq’s full 6C33C would not be enough? Surely it would be possible to go for transmission tubes but they all high plate impedance and high voltage.
If I parallel all my bass drivers and have around 1R load impedance then it will be a transformer with zillion turns… Also, I am not a big fun of the transmission tubes’ bass.

Adding more drivers in bass array look promising but not necessarily effective or practical. So, it would be interesting to find a high current tube that might be sitting in Milq’s bass channel socket. Since I so like the sound of 6C33C it would be worth to mention that the 6C33C has a bigger brother: 12C42C

The 12C42C was a next tube in the succession or 6C19C, 6C41C, 6C18C/6C33C. The 6C41C had one plate the 6C18C/6C33C were two plated and the 12C42C was simialr tube to the 6C33C but with 3 plates!!! It is not enough to be become purring – look at the 6C33C data:

Filaments: 12.6 and 5A
Anode voltage: 120V
Anode Current: 1A
Plate impedance: 65R
Maximum Anode dissipation -120W

Whonna to drive dead woofers with single ended triode? Get the Bell Laboratories 320A tube.

The 320A Vacuum tube was designed for use as an oscillator, modulator, or amplifier at the higher power levels
and high frequencies.

Filament ratings: 35 volts at 435 amperes
Average thermionic emission: 90 amperes
Characteristics at 18 kV plate voltage and 8 amperes plate current:
Amplification factor: 30
Plate resistance: 965 ohms
Transconductance: 31,100 micromhos

Maximum plate voltages: 12.5 kV modulated, 18 kV non modulated, 20 kV RMS AC
current: 15 amps DC
dissipation: 150 kilowatts

Maximum grid dissipation: 2 kilowatt

http://www.goodsoundclub.com/pdf/GU48.pdf

Romy the Cat wrote:

There was a cool Russian-made tube GU-48...  I do not think that it would be worse; in fact I think it might be even better…

Nope, the Russian tubes generally much, in fact much worse than western equivalents. There were however some exceptions. Those options were due to various reasons. The tubes like GM70, YO186, 1P24B, 6E5P, 6N30P, BO188, GM57, UB180, 6C33C, 6N6P, M457, ТО-143, YO104 were very-very good. The GU81, GU48, GU29 were generator tubes and they are presumably OK; I did not hear any good-made amps with it.  The GM70 is transmitting tube as well and it is exceptionably good tube also, way more superior then 211/845 tubes but it is kind of not used yet tube as no one so far made any decently sounding amp with it, at least among those that I heard. So, the Russian transmitting tubes from the GU line might be fine tubes. To make an amp with them is a totally different subject…

What surprises me however is why you have expressed an interest in the high power tubes? You are with horns and even you LF sections have over 100dB sensitivity. What will you do with 120W SET?

Anyhow, I do not have a circuit for this type of amp. The circuit is not a problem, to know how to get sound out of those tubes is the problem and I have no knowledge about it. In the world of transmitting tubes the tube never was a problem. The right output transformer is the problem. It might be VERY expensive to make it properly and it might be very unnecessary due to the existence of DSET concept. Still, to hear a 120W SET over a few days might be a fan experience …

Romy the Cat wrote:

What surprises me however is why you have expressed an interest in the high power tubes? You are with horns and even you LF sections have over 100dB sensitivity. What will you do with 120W SET?

drdna wrote:

The subwoofer still needs a substantial power source. Right now it is being driven by a solid state amplifier.  It would be interesting to see what impact the SET could have here if any.

I see, I did not know that subwoofer needs a substantial power source. If so then sure it might be interesting. To make from GU-48 a powerful LF DSET would not be difficult.  The output transformer will be very simple as well. The high voltage transformer for transmission tubes usually screen up HF as they need excessive high voltage isolation but for LF only DSET it would be no brainer. Make 500mA transformer with larger lamination you will be able to found and coils with 3000V-4000V isolation. I think if you find somebody why would  make it large enough to get 5Hz-7Hz at FULL POWER then it will be around 500-700 transformer. Everything else will be relatively easy if you can talk like this about an amp hat will have 1.5kV on plate. BTW, the GU-48 has high gain, so who know it might be even a single stage amp…