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RE: Maximum Output

What CB said.

Also, when you change the idle current you also have to change the voltage and the load impedance to keep the harmonic distortion low.

This is something Dennis doesn't do.

He runs his 2a3 into a 2.5k ohm load, which would be fine for his 250 volts if he kept the plate current at 60ma. but at the 43ma. plate current that he runs, the harmonic distortion would be lower at all power levels if he loaded the 2a3 with 3.9k ohms.

Paul Joppa has a quick rule of thumb that works really well. Load impedance, for a reasonable amount of output power keeping the harmonic distortion reasonably low, = (voltage / current) - (2.38 * the plate resistance)

This follows the Western Electric performance chart and the on line Triode Loadline Simulator very well and is a good rule for all direct heated power tubes.

http://www.trioda.com/tools/triode.html

It's really not about the max power, it's about low distortion at all power levels.

The output stage of Dennis' amp could produce 1/3 the distortion at 1 watt that it does if he just used a 3.9k output transformer instead of the 2.5k output transformer.

But I don't think Dennis understands tubed audio electronics very well so he's gonna do what he's gonna do. It's hard to teach an old dog a new trick.

Dennis is going to point out that a output transformer with higher reflected primary impedance requires more inductance and more wire and there will be more winding capacitance, etc. This is all true but a good winder can wind a 3.9k to 8 ohms output transformer with good frequency response or we can have a custom transformer wound that doesn't have so much inductance. That would keep the winding capacitance low but the bass frequency response would suffer. IMO, a SET shouldn't be playing bass in the first place. That's what Solid State amps are for! :-)

Anyhow, just don't get hung up thinking Dennis is some kind of Guru, he's not.

He's just a builder with a very large ego who thinks he's God's gift to the world, but he's not.

There are a lot of good builders here who know a lot more than Dennis.

Tre'


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"Still Working the Problem"

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