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Old 27th September 2009, 08:33 PM   #1
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Default tube phasing for more power?

This might sound weird, and I certainly don't hold the key to all the answers, so my question might make you laugh or not.
Is it possible or even a good idea to phase 4 tubes in such a manner that each one shares a portion of the sine wave? yeah I hear the laughing. No I don't mean 180-180 degrees as a P-P. I mean each side of the push pull contains two tubes, not in parallel,(4 tubes total for amp) but say the first tube goes from 0-45 degrees and again it goes from 90 to 135 degrees. The second tube from 45 to 90 and again from 135 to 180. Or something of that nature. The third and fourth tube do the other half of the cycle.The thought is to push more power from the tube than possible with class A, B etc.
Just thinking one might get twice the power than with 2 tubes in parallel each side. so instead of four 6AQ5's doing 20 watts get 40 watts, for example. Is this just a bad idea and a waste of server space?
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Old 27th September 2009, 08:53 PM   #2
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ah ;p i see.

would work best with single frequency or square wave signals (simple predictable signals)

and, well, a tube is a tube, average power will be the same, work twice, rest twice so to say.

it makes me think of a system where every 5 seconds another bridge carries the load.

but fun topic
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Old 27th September 2009, 09:01 PM   #3
m6tt is offline m6tt  United States
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I think there are a couple of issues. I've never heard of this being tried in audio, but it looks like class C operation. In other words, each tube conducts for less than 1/2 of 360 degrees. The issues I see are 2x crossover distortion, since the output tubes collectively will "cross zero" 4 times per 360. I am also not sure whether this requires something like two p-p transformers or four SE transformers...or how to exactly set this up bias vs. grid voltage wise. This also seems like it would be much more sensitive to the power supply, since you have a couple of big current draws happening suddenly, but they might cancel enough.

It's an interesting question, but I worry that if it worked well that Bogen or some other PA amp manufacturer would have already done this since they'd have been able to effectively double the power and thus the value of their equipment when watts were at a premium. That being said, you'd think the Roman empire would've invented the airplane too .
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Old 27th September 2009, 09:02 PM   #4
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I see.. makes you think though. I was thinking something like that. Using some form of feedback from one tube to control the grid of another or just use ic's. yeah more like class C but combining the two, to end up with a different class.I would be willing to try it

Last edited by yourownfree; 27th September 2009 at 09:06 PM.
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Old 27th September 2009, 09:19 PM   #5
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well, what really sets class c apart is that the tube conducts only hard, with little voltage across it (say peak of sine).

but one may need to run it at rf, and use some sort of high power demodulator to listen to it ;p

or equivalently, use a resonant output circuit, for 1 single tone, or listen to square waves.
or, many many ones combined to a wideband output.

a sortof analog wavelet amplifier ;p

Last edited by jechentau; 27th September 2009 at 09:25 PM.
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Old 27th September 2009, 11:57 PM   #6
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Efficiency comes from keeping the voltage across the tube minimized. Class G or class H do that by using multiple B+ levels for multiple tubes or by tracking B+ levels for one set of tubes (tracking of the audio envelope + some margin). Commonly done for SS amplifiers, could be done for tubes too. Problem with tubes though, is that they require a lot more minimum voltage to operate than SS devices.
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Old 28th September 2009, 12:37 AM   #7
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wow, a lot of info. I can also see that if switching was done the frequency of the switching would be a problem and be just noisy as heck probably. OK bad idea, but sure was interesting to dissect.
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Old 28th September 2009, 03:00 AM   #8
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Ah, guyz,

There's a way to divide up the power of the audio signal between tubes, without all this signal division and switching and other difficult/impossible to transparently implement elaboration.

It's called parallel operation.

Occam often has it right, y'know.

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Old 28th September 2009, 03:50 AM   #9
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Well, one could just cheat:
This could also be seen as class H (tracking rails) if the tube amp is implemented using pentodes, since the SS amp would effectively be feeding a tracking B+ back thru the output xfmr to the plates. Using triodes though looks more like series connected amplifiers, due to their low plate Z allowing SS bleedthru.

Another way would be to use tubes for the lowest power level of a class G amplifier, and Mosfets for the higher power (and B+) level(s). A similar setup that has been used before has triodes for the 1st level and pentodes for the higher power level. Grid biasing determines when each tier parallels in.
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Old 28th September 2009, 04:14 AM   #10
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I made class A+C amps, they sounded very nice. Both SS and hybrids. However, I never did class A+C with tube outputs, but it is possible.
The Devil is not so terrible as his math model is!
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