Decrease to 0 hummm in Scott 340 B

There was hummm, caused by ripples on first el. cap after rectifier about 4.5 V. Rectifier is SS with 4 diodes. Schematic use cap 20-40 uF, that doesn"t enough for filtering. If rectifier is tube, ripples will be about 2-3 times less and caps 20-40 uF are enough. I added 68 uF and humm is gone.
Usually, if I use SS rectifier and I use for first caps 200-300 uF /not 20-40 uF/ and Iron chock. If I use tube rect. I put no more 47 uF. Tube rect. gives 2-3 times less humm. It can also be caused by increased current in output tubes, that increase ripples in PS /increased current, multiplied to inner R of PS,  gives increased ripples/, and current needs  adjusting. Sorry for not good English. 
If someone needs help, Im ready for it, but, sorry, only in Baltimore MD.

Showing 1 response by azazello

I think, this filter group is from old model Scott with tube rectifier. In next model tube is changed to SS rect, but filter remains the same, because SS rectifiers need caps value in some times more....first 100-200 uF and next - 300-400 uF. /In Scott  340B rectifier is SS with six caps 20 uF, that IMO is wrong, IMO/.