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In Reply to: RE: 500c buzzing power transformer posted by floydandrews on March 29, 2014 at 13:48:48
Floyd
I wonder if the power transformer was changed because I own five 500c and one 800c receiver and not one is riveted together nor are the many I rebuilt.
Just disconnect the two power supply diodes in the doubler..You only have to lift one end of each. If the buzzing goes away,I have seen shorted or leaky filter caps in the chain cause loud transformer transformer oscillation on occasion.
Honest amplification is better than excessive 2nd order distortion anytime.
Follow Ups:
Thanks for weighing in. The transformer looks like it belongs. No extra mounting holes in the chassis.I removed all the tubes and disconnected the voltage doubler rectifiers before the first time that I plugged it in. Didn't want a bad cap to spoil the whole thing. Since I posted the original query I have put a bolt through one end of the end bells and tightened it down. Still vibrating like it wants to take off. Next step is to disconnect all the secondaries right at the transformer and check the current draw. Currently the tubes are out, the B+ rectifier is disconnected, but the filament wiring is still connected and the rebuilt (new rectifier and caps) bias supply is connected.
Edits: 03/29/14
Floyd
If you disabled the diodes and pulled out all tubes,that pretty much disables any load on the transformer secondary..The only left is if you want to disconnect the selenium rect bridge on the side..Can you post a photo of the power transformer?
Honest amplification is better than excessive 2nd order distortion anytime.
Amps that I've worked on with heavy mechanical buzzing or vibration sometimes benefit from re-lacquering the laminations. Some ppl have inserted rubber bushings to isolate the tranny from the chassis, reducing the buzz from resonating into the chassis.
Here's a photo of some such arrangement. Maybe, it'll help.
Steve
Yes,that can work..Ebay many times has Fisher 500C power trannies that people throw on there for 50 to 75 dollars from 500c and 800c carcasses they have parted out.
Honest amplification is better than excessive 2nd order distortion anytime.
Thanks for sharing.
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