It looks like it drives the filaments of the tubes? So one diode clips the AC wave to keep it from being noisy? I AM GUESSING? HELP! I noticed in schematics for old radios they call Capacitors, Condensers. I think it is a term thing I am confused about "Rectifier". Been causing troubles to tube amps since late '90s (I recall the early days of Ted Weber's Bullettin Board.I understand it is advantageous to replace the Selenium RECTIFIER which a single Diode (not a rectifier Bridge). I was wrong and now I'll medidate about it in the long and boring time required by troubleshooting the consequences of my superficiality. I supposed I knew what the schematic meant.
Lesson learned: never start modding an old amp before you are not totally confident about what you're doing (never messed with bias rectifiers in the past). All the rest is a different matter, probably off-topic according to thread's subject. Quite an hassle to figure out the layout assuming I'll have to use single caps to place somewhere in the chassis.Īnyway, the selenium rectifier replacement was completed. I guess the three cans will have to be replaced. I know I should have already replaced them all but since the amp was working fine (no hum nor noise) I started from the old selenium rectifier. You may have damaged the bias filter caps by reverse voltage.Īre the filter caps original?Yes, they're still the original filter caps. This positive current charges the connected side of the cap to a positive voltage. Thanks.Positive transformer current flows from diode anode to cathode (marked side). It looks like the bias circuit is now far from specs.ĭid I assume it was too easy? Can you see any big mistake in what I did? At this point I guess the original resistors values do not match the new scenario with IN4007 diode. When I switched on the amp (no power tubes for safety reasons) I measured a totally different bias voltage: -26.80V (selenium, tubes installed) vs. The diode cathode (marked side) was soldered on the - side according to the schematic. So I installed a IN4007 silicon diode in place, also replacing the two old 20/150 caps with 22/450 double checking proper polarity (+ to ground). It was still working but I know they're famous for failing after so many years. I convinced myself to get rid of the old selenium rectifier in the bias circuit of an old Dukane 1U460 PA.
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