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Re: schematics for 6C33 single ended OTL?

Posted by Ralph (M) on July 13, 2006 at 10:11:32

In Reply to: Re: schematics for 6C33 single ended OTL? posted by tubetvr on July 13, 2006 at 01:47:34:

You are right- I hear about this one often! However it always comes down to the same thing- our power tubes don't go into cutoff (which is easy to measure BTW) unless the amplifier is driven into clipping. That seems to be the easiest way to distinguish Class A.

*Any* OTL can be class A, and our amps were/are not the only ones ever made either. Like I said, its all a matter of plate voltage and biasing. Many manufacturers have chosen not to go class A because of the heat and I concede that the heat has been a marketing problem for us (people often assume that our amps run hot because they are OTLs, which is not true, it runs hot because it is class A).

Some are unhappy with us because we have an A2 window in our operation (like Fisher did back in the 50s). The 6AS7G begins to develop grid current before the grid goes positive with respect to the cathode. So we designed our driver circuit to accomodate this. But Class A2 is still Class A by all the textbooks I have seen.

You might try it. You will have to lower your plate voltage somewhat to avoid burning up the tubes when you increase the bias. The difference in sound is instantly audible- Good Luck!

All the Best,

-Ralph

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