Need some 500C help

Jailtime

Standin' on a corner
I have a "restored" 500C here that I fired up for the first time today. I didn't do the work on it. It has the basic restoration, silicon rectifier, coupling caps, and fuse resistors. Still has original can caps. I ran it on my variac so I could control line voltage, my line is a bit high (124V).

I measured 465V on pin 3 of the 7591s (should be 430) and 410 on pin 8 (should be 375). The resistor after the rectifier is the original value. Possible cause for the high voltage there? The right channel has distortion in low frequencies. There's also a whistle in the right channel, doesn't matter what input or volume setting. All the tubes were tested with Maxi Matcher testers. I'm not very happy with this performance from a unit that was "restored".
 
I have a "restored" 500C here that I fired up for the first time today. I didn't do the work on it. It has the basic restoration, silicon rectifier, coupling caps, and fuse resistors. Still has original can caps. I ran it on my variac so I could control line voltage, my line is a bit high (124V).

I measured 465V on pin 3 of the 7591s (should be 430) and 410 on pin 8 (should be 375). The resistor after the rectifier is the original value. Possible cause for the high voltage there? The right channel has distortion in low frequencies. There's also a whistle in the right channel, doesn't matter what input or volume setting. All the tubes were tested with Maxi Matcher testers. I'm not very happy with this performance from a unit that was "restored".

I'd start the investigation with the can caps...

-D
 
Adjust your variac until the filament voltage on one of your output tubes reads 6.3VAC. Then remeasure your plate and screen voltages and see what you get.

Chappy
 
What are the output tubes drawing? Sounds almost like they are pretty well worn and not pulling down the voltage like they should.

Set the variac to 117. Check the plate and screen voltage, bias B-, and the heater voltages on the 12AX7's.

Something to note here. FISHER does state on the schematic that at the correct input voltage, voltages in the unit may be off by as much as 15%. This is due to variances in components and allowable. or words to that effect.

Larry
 
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