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In Reply to: RE: se 12av5 posted by hennfarm on March 31, 2015 at 23:26:53
Lousy cell phone pic... 460v shotkky bridge , 4H 140uf then 2H 160uf to each 12av5 And 3H 15uf to each 12hl7. 50H and 2500ohm plate load on 12hl7s. Edcor15w 3.5k opt. I'm adding a standby switch, front end poly caps do not like 630vdc when the supply soars on power up. Many salvaged parts, I wound all inductors but the plate chokes. Mars motor run filter caps. Separate transformer for Bridge rect. Bias, CRC. Separate fils tx for each channel. Initial garage impression: very nice, bass is a bit flabby. 12hl7s @7w bias. 12av5s @ 16w. 414plate -89 g1. Maybe some day I will build around some real triodes :-) JH
Edits: 03/31/15Follow Ups:
A solid-state rectifier with choke input needs a small cap or an MOV to ground after the rectifier for surge suppression. .05uF will do, make it 1000V or more. Shunting the input choke with a lower voltage MOV will do as well. I can show you shorted 1400V rectifiers if you'd like some proof...
Makes sense as I have at least one other ss rectified choke input supply that has killed generously overrated diodes for no apparent reason. Perfect place for one of those odd 12kv sprague tv caps I have. Thanks. JH
Fun! Designs look a lot bigger in person when built versus on paper, eh?
A standby switch could work on your turn on surge before the current through he tubes is enough to make the input choke see a critical load. (An different way of doing this is to use a 5AR4 rectifier.)
Alternatively, you could provide a load for your power supply so that the input choke works before the tubes fully conduct. If you wanted 20mA at 400 volts 400/0.02= 20,000. Put a 20K 20 watt resistor to ground near the end of your power supply filter and it will keep the turn on surge down.
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