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Tube Single Ended Triode Questions??

Why can't SETs be built with more power and able to drive a bigger range of speakers? I know the 300B tube can goto 10 Watts or so, and the 2A3 in only 2W, but why can't they do an amp that is like "single ended parallel" with several amp stages in parallel? Or, why can't tubes be used like EL34, 6550 and KT88s (I guess these are known as power tetrodes) and make higher power SE amps? I guess the idea behind SETs is to avoid splitting the siginal into push-pull and they are class A, but you give up a little S/N ratio with a SE circuit - is this correct? Are some tubes too noisy to run single ended, or can only a portion of a KT88 be used in SE mode?

Also, the output transformers- is this really what seperates okay from great SETs? Are quality transformers what makes them so expensive for what appears to be a very small parts count?

I have some question for latter about SE -vs- Balanced preamps too - is it a simialar trade off to SE/BAL amps, but I will save that for latter.
6550c
almarg's avatar
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almarg
9,670 posts
 
Wonderful explanation, Ralph (Atmasphere). Thanks!

Best regards,
-- Al
rockadanny
1,224 posts
 
Victor - Please tell me how many watts maximum two parallel 6C33C tubes should be able to generate if not 45/50?
victor_hrynchuk
4 posts
 
One 6c33c in class A will provide you with something around 18 Watts. Two tubes theoretically will provide twofold increase, but only theoretically. To do this they must be supper precisely matched and for 6C33C it is practically impossible, so on peaks one tube with bigger current will swamp another. I believe you can get 30 Watts for from parallel 6c33c SET amp. The only way to get 3db increase of power from paralleling two tubes is to use two independent power supply , two output transformers and parallel the secondaries of the output transformers. The solution is very expensive.
tdelahanty
12 posts
 
Push/Pull amps make more power because they are more efficient, each tube only conducts for 180 degrees of the input signal hence the term push/pull. This allows each tube's plate to cool down while the other tube is conducting, giving greater average power. I doubt distortion is created by a properly designed phase splitter. The trick is avoiding crossover distortion. The area of zero conduction where the two halves of the sine wave are put together is the weakness of P/P designs. The way to overcome this nonlinear region is to make each tube of the P/P output ckt. conduct for slightly more than 180 degrees.
atmasphere's avatar
atmasphere
11,794 posts
 
Tdelahanty, what you are describing is known as 'class B' operation. It is also possible to have a class A push-pull amp, where both tubes are always conducting throughout the entire signal, even at full power.

This makes for a better sounding amp, and is still more efficent than single-ended. The only way to avoid the degradation of the phase splitter is to build it into the voltage amplifier, IOW make the voltage amplifier fully balanced.
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