PP design ideas @ 100mA HT current

[fyzygy]

I'm curious about the HT current requirements of various push-pull circuits, including the 18watt family. According to the Rob Robinette website, a Fender Deluxe (6V6 push-pull pair, plus a pair of preamp tubes) requires under 100mA of HT current. But that's driving the tubes with a voltage considerably higher than recommended (presumably, for more gain). And the 18watt schematics seem to call (more reasonably, perhaps) for a 125mA HT secondary. I have a few power transformers rated for 100mA. Can I build some kind of 18watt mutant with these? I'm guessing the answer could well be, at what range of voltages? Looking through data sheets, 6V6 does appear to be less current-hungry than EL84. Though perhaps something like 6AQ5 could be a better match? I dunno ... what would *you* build with a 100mA HT secondary capable of supplying around 300v?

A related question is to what extent a power transformer can be pushed beyond its rated limits (having read that some classic guitar amps use under-sized power transformers, rather than overbuilt ones). I'm guessing the answer to that depends a lot on quality, type and construction of the transformer in question. And ... do I wanna risk it?

[Bieworm]

About the 100mA sec current. I think it makes no difference using EL84 or 6V6 type tubes. This is the current the amplification circuit will tap off. The available heater current on the 6.3V sec is more important when choosing tubes for the amp.

The only thing you will notice when the HV sec is choking out is when you’re playing on its limits and beyond is a lack of punch and clarity. There will be better mathematical explanations for it, but simply put you will not get what you need. OTOH you could definitely try it. A power transformer is easily changed. Watch out for the over heating. This transformer will be suitable for Princeton Reverb kind of amps.

[JMPGuitars]

The simple answer is less tubes. For example, one of the "Lite" 18 watt variants will require less secondary current. Superlite TMB or Lite2b or Lite2p(ef86).