SET amps sound good in the midrange and higher frequencies, but the real thing to listen for is bass performance. That's the hard part for a SET amp. Most loudspeakers require electric motor braking (literally) because the main part of damping in the T/S specs is electrical, not mechanical. So the output impedance is very important to bass response. If the bass sounds boomy or tubby, try it with a PP amp and see how you like it.

How is life going in the world of Pi?

I want to thank you for the kind offer of hooking up your Audio Note 2 SET to my friends Jordan speakers.

My friend Mike, who lives in Seattle and I have discussed the Audio Note 2 SET as an option.
But, he feels that the 12 watts is not enough to drive the Jordan transmission line speakers. He feels since the Jordan's bottom frequency response goes down to 45 Hz and is 88db efficienct at 8 ohms, that it will not have enough authority since he likes to listen to classical music.
Also, since he lives in Seattle, it would be diffacult to hook up the amplifier with out a dangerous jouney across our land at the hands of the delivery wrecking crew.

I for one, am not convinced that 12 watts would not be enough power to drive his speakers well. Obviously, a 5" full range driver is not the best choice to play classical through in the first place, possibly at lower listening levels though. I think that is why he feels 20 watts should be at the lower end of the amplifiers output capability.

His thinking is some what stuck in the direction of a triode based SET amplifier to obtain the last degee of musical purity.
I again, am open to any suggestions that would get us there, triode, pentode, SET, or push pull, I'm open.

I have been trying to get my friend to build the 7591A version of Poindexter's Musical Machine with some Sansui 1000A output transformers, but he is not ready to do so at this time.

Thanks again and I hope someone can chime in with other DIY amplifier designs and suggestions.

Norris

But as the signal swings more and more, the DF varies more and more in an SET than a PP amp as the Ra is changing more in an SET triode while the PP triode combo is more constant. Theoretically, as one triode's Ra is rising, the other is lowering, maintaining an approx constant.

This Ra swing occurs in all triodes, with the Ra varying from several hundred ohms to thousands of ohms and eventually (theoretically) infinite ohms at triode cutoff.

• http://usuarios.uninet.com.br/~edelima/

• http://audioroundtable.com/Tubes/messages/790.html

It might be partly symantics Damir, so I will say the output Z and subsequent Damping Factor changes "somewhat".

Even with a relatively horizontal loadline, the plate current should be held as high as possible, or keep the power down so the signal doesn't swing near the tube's cutoff.

Specs from 300b data sheet (since that is the tube you mention.)

At 60ma idle current at 100 volts or above, tube Ra is approx 600 ohms. At the 30ma point of the loadline, the Ra is approx 1000 ohms. The DF is no longer 3, but 1.8 at the 30ma point. (This means a peak to peak current swing of 30ma to 90ma. One can figure the output power from there.)

At the 20ma point, at 100 volts or above, results in an Ra of approx 1200 ohms, double the 600 ohm Ra at 60ma. This means that a DF of 3 now becomes a DF of 1.5 at 20ma.
(This means the current swings between 20ma and 100ma, with 60ma as quiescent.)

If the plate current is allowed to drop to 10ma during a portion of the cycle, the Ra is approx 1450 ohms. DF now becomes 1.25. (peak to peak swing of 10ma to 110ma.)

At 5ma, the Ra increases to approx 2000 ohms, or nearly 3 times that at 60ma. Df becomes approx 1. (peak to peak swing of 5ma to 115ma.)

As the tube approaches cutoff, the Ra rises towards infinity till the tube isn't actually conducting.

PP has virtually no drop off of DF, except because of variations in individual tube characteristics.

PP therefore does not offer such a compromise in Damping factor as SE operation does.