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Questions about tubes and gear that glows. FAQ

Re: Unbalanced double triode creates unbalanced speaker output?

Anthony V wrote...

"Supposedly,you never want one side of , say, a 12ax7 to test any lower/higher than 10 % of the other side ( Yes/No ?? )."

Tubes that have sections within 10% are not all that common. And in the VAST majority of aplications it makes no difference at all. And, BTW, 10% of WHAT?? Cathode current, transconductance, what?

"If the above is correct, then does it stand to reason that one should expect to hear/measure a 30% reduction in channel output at the speaker if the first (V1)tube in say a three tube line preamp section has a measurement of 100/70, but the following two tubes ( V2 and V3 )measure 100/100 and 100/100 respectivly?"

Absolutely not! This is because it isn't the tube alone that determines the circuit's gain, it's the entire circuit. Well designed circuitry works properly with a wide variety of tube characteristics. They have to, since tube characteristics change as the tubes age.

Even if you did have different levels of drive to the output tubes, negative feedback in the amp tends to correct for it.

This is one reason why I keep telling people that matched small signal tubes are by and large a waste of money. Yes, a few circuits can benefit (or maybe even require) them, but VERY few of those are audio circuits.



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