If you anyway wish to replace the vacuum rectifier with a solid state =
one, using a voltage dropping resistor is a silly way to go, as it would =
impair the power supply regulation.

My suggestion is: after measuring the voltage increase you have with the =
solid state rectifier, just put an appropriate zener diode in series =
with the DC line. The zener diode causes a fixed drop and does not =
impair regulation.

If, for your application, a high-power (and hence expensive) zener diode =
would be needed, then use the well-known zener diode emulation circuit =
(a power transistor and a small zener).

73

Tony, I0JX

"William Mutch" ha scritto nel messaggio =
ell.edu...
I'm curious about what is invloved in converting boatanchor=20
(specifically my NC-125) power supplies from tubes to solid state =
bridge=20
rectifiers. I understand that most guys will mount the bridge and=20
dropping resistor on a tube socket so that the conversion is easily=20
reversable. How do you determine the difference between (a) the=20
voltage drop of the tube and the solid state bridge, and (b) the =
working=20
current so that you can calculate the appropriate values of the =
dropping=20
resistor and its power rating ??=20
Is there any point to converting the 6.3 volt filament string from =20
from the ac bus, running all over the chassis spreading 60 hz hum=20
wherever it goes, to 6.3 volt filtered DC, a rather easy thing to do =

these days. Has anyone done this ?? Is it worth it ?? what issues =
were=20
involved ?