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In Reply to: RE: Get 'Em Out! posted by Eli Duttman on January 20, 2017 at 14:45:34
While this is all true, a silicon rectifier is not a direct drop in replacement. First of all there is considerable forward resistance as well as reverse leakage in a selenium.
With silicon you are going to have a higher rectified voltage, and a higher peak current as the diode turns on. This may make noise in the supply.
Most effective would be a resistor in series with the silicon. I did this and it worked, but that was an ultrasonic cleaner. For audio I would also put a capacitor across the silicon, not sure of what value, that would depend on the application as does the resistance and wattage of the resistor.
One thing to really watch is the voltage. This equipment (in the US) was designed to operate on 107-112 volts, now nominal line voltage is 125. This wreaks havoc on old tube guitar amps no matter what kind of rectifier(s) they use. I have had to bias quite a few of them almost all the way down (in current) to get them to stop redplating at idle. What happens when they turn it all the way up is beyond my control. Ideally they would buy a bucking transformer but they are cheap. At least where I used to work on them. When the ticket says "call if over $20" you know they are not going to spring for a transformer. In fact that is one of the reasons I no longer work there. That and the fact that most of them are clueless, they have no conception of mic/guitar level, line level and speaker level. They have used guitar cords for speaker connects on 200 watt amps, and then speaker ¼" lines for a guitar and wonder why it hums.
Anyway, a choke in series with the silicon rectifier might work well, but there will have to be some capacitance across it to keep the inductive voltage in check.
Follow Ups:
Changed resistance to get the voltage right is important. Noise is easily solved. Use Schottky diodes, with ZERO reverse recovery spike. :> D
Eli D.
Thanks you guys. I got some great ole advise. Mark K.
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