I recently prototyped a small SE stereo amp using a toroidal power transformer, and I'm not reaching the voltage I expected after modeling with PSU Designer II.
Before I built everything I measured the voltage from the secondary and read 250 volts. I was expecting a healthy rise in voltage from a large first cap to arrive at a B+ of 300v or so. However I found that as the tubes warmed up my voltage dropped leaving me just 268v on the output plates and far less on the driver. Measuring the secondary AC again I now have just 230v, so I lost quite a bit. The circuit is designed to draw about 75ma. The transformer is rated for 100ma at 50va. I think I need a beefier transformer but I'm unsure how robust I should go. Is there a rule of thumb for what the trannies' rating should be in order to sustain the voltage rise I'm aiming for?