"Antonio Vernucci" wrote



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).

***In the vast majority of receivers that I have come across,the power
supply loading is more or less constant,the main drain being by the audio
output stage which is almost universally a class A amplifier.Hence power
supply regulation is
of no consequence as the load is static.Fitting a resistor will drop a
constant number of Volts,try it and see.

Brian Goldsmith.

What you say is specifically true for receivers; it is obvious, no =
reason to try and see it as you suggest. But that is not true in the =
general case (e.g. transceivers).

Moreover, using a resistor, voltage will only drop only once tubes will =
have warmed up and drain current. With a zener instead voltage will =
immediately drop (e.g. any minimal load caused by an high-value resistor =
anywhere in the circuit will be sufficient to have the zener dropping =
voltage).=20

In some cases it is important to NEVER reach a voltage higher than =
specified. I had a bad experience at that regard with 6146Ws fed by a =
Collins power supply where the vacuum rectifier had been substituted by =
a solid state one. Two new 6146Ws immediately flashed and were damaged. =
A zener diode solved the problem.

73

Tony, I0JX=20

***In the vast majority of receivers that I have come across,the power =

supply loading is more or less constant,the main drain being by the =
audio=20
output stage which is almost universally a class A amplifier.Hence =
power=20
supply regulation is
of no consequence as the load is static.Fitting a resistor will drop a =

constant number of Volts,try it and see.
=20
Brian Goldsmith.=20
=20

"Antonio Vernucci" wrote

What you say is specifically true for receivers; it is obvious, no reason to
try and see it as you suggest. But that is not true in the general case
(e.g. transceivers).


**** In the case of a transceiver using a vacuum tube rectifier I would
expect the B+ to drop as the forward Voltage drop across the diodes
increases with load.

Brian Goldsmith.