21-CT-55 power supply failure

[Penthode]

Not a good idea to calculate the resistance needed based on the DC (average) current. It might be right but probably won't be. The voltage drop actually depends on the instantaneous charging current, and that depends on the size of the filter caps and how much ripple is on those caps.


Why not just try different values until the B+ is what you want?

Phil Nelson

I believe that is what Wayne was implying. The overall forward resistance of the silicon diode plus added resistance must match the forward resistance of the original selenium rectifier. This should maintain the instantaneous charging current.

The net result of the properly chosen extra resistor will ensure the same ripple. Hence the resistor is chosen to match the original B+ voltage.

Terry