Motorola B12WA recap and mods

[wa2ise]

Originally Posted by maxhifi

Does the full wave rectifier raise the B+ enough to require changing the operating points of the tubes? (Specifically the audio output?) is there a meaningful reduction in hum?

The plate voltage is pretty much the same, with lower ripple. Yes, 120Hz would be somewhat louder than 60Hz with the usual AA6 speaker (this radio has a bigger than usual speaker and a wooden cabinet), but ripple contains higher frequency components which is what you mostly hear with ripple. The ripple amplitude is roughly half with the bridge rectifier, and I used bigger filter caps than the originals (which also helps). But is it meaningful? A manufacturer probably would not have spent the extra pennies for the extra diodes...

I changed out the ceramic coupling caps in the audio path with films.