Converting 5U4 to solid state

[old_coot88]

Originally Posted by bandersen

Oh wait, I think I see what you're getting at. Since the silicon is more efficient, the resistive dropper will have to waste more power than the less efficient 5U4.

At the risk of being a fuddyduddy, I would amend that slightly to read thus:
"Since silicon is more efficient (ie., fully "switched on" during its entire conduction period), the resistive dropper and the transformer's HV winding will be forced to dissipate more power than the less efficient 5U4."
The Si diodes' "square" conduction period presents longer "fully on" time than a vacuum diode's 'bell' curve. "Higher duty cycle" if you will. Thus the resistive dropper and the HV winding see greater net loading, power dissipation and heating.

It'd be interesting to do a real world before-&-after test with a wattmeter in the AC line, and a thermometer on the power tranny.