some cranky ideas and questions

[Joe Bee]

Since my vanilla clone amp is working so well, I feel drawn to some more exotic amp topologies to play with, not neccessarily because I think they will sound good but just too see whether it can be done.

1) The russian 6R2P dual beam tetrode. I think it would be neat to put a PP power amp into a single tube, and this one seems ideal as it is not as prohibitively expensive as the european ELL80 and ECLL80 tubes. If it performs at all similar to two 6V6 in push pull, it would make for a nice little amp, wouldn't it?

2) Cranky power supply schemes: Since I have a bunch of those PL84 tubes that need 16V on the heater, but no transformers that would provide it, I tried using a voltage doubler on a 6.3V winding. It works, but I wonder if the distortion on the 6.3VAC waveform will make it unsuitable to heat preamp tubes anymore? I don't really want to mess with DC heating (other than on the power valve) and make thinks even more complicated.
Also I want to run the PL84 on only 100V or so of plate voltage, while the preamp needs about twice that. I am considering another voltage doubler for the preamp...

3) Push pull without the center-tap. I am a cheapskate and constantly trying to recycle old power transformers for OT. They cant do single ended for lack of an airgap, and they cant to PP without a center tap. Or can they? Maybe the Totem Pole / SRPP / SEPP topology would work well here, is it worth trying out?

4) Last and least, since I am not a believer of the saturated power whatever mojo: An SRPP of two EF86 to simulate power amp clipping somewhere in the Preamp?


Tell me what you think....

[Don Moose]

2) Cranky power supply schemes: Since I have a bunch of those PL84 tubes that need 16V on the heater, but no transformers that would provide it, I tried using a voltage doubler on a 6.3V winding. It works, but I wonder if the distortion on the 6.3VAC waveform will make it unsuitable to heat preamp tubes anymore? I don't really want to mess with DC heating (other than on the power valve) and make thinks even more complicated.

The only place DC heaters make any kind of sense is on the first preamp tube - that's the one most sensitive to heater noise.

A voltage doubler is also a current doubler - they are constant-power(+losses) circuits. To get 2V out you're gonna draw at least 2I in. The voltage distortion they produce shouldn't matter, except at the first triode of a real gainmonster preamp.

Hope this helps!