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VTL hum on both channels

I have a VTL 75/75 which I purchased recently. Both channels have a slight 60Hz hum. I tried the cheater plug, isolating the amp from the rest of my system, and using a RCA shorting plug to see if it was coming from somewhere else but it seems the amp is noisy.
I even connected a Sola power conditioner for a try.
I was able to download a schematic from the internet for a 50/50 which is similar to the 75/75 and got out my scope. I could see a 60Hz signal on the output at the speaker terminals. Checked all the power caps and had hardly any ripple. The only place where I saw the same looking signal was on the bias power supply. The DC voltage is around –50 volts with around 1 volt of ripple. Being new to tubes I do not know if this could be a cause of the problem. The capacitor in the circuit is 47uF at 100 VDC. I was thinking of increasing the value to see if the hum went away.
Any help would be appreciated.
fixer53

Showing 1 response by fixer53

fixer53 OP
1 posts
 
I put in new caps. I replaced the 47uF with 500uF and added a 250uF right after the rectifier. What I have is a 4 diode rectifier that had no filter cap, then a 90 ohm resister going to the bias pots. Thats where I increased the capacitance. The ripple went from around 1Vp-p to about 20mV p-p. Still hear noise. Can't hear it when music is playing but I know I will obsess over it.
On the schematic for the 50/50 there are caps (100uF @ 100VDC) going across all 10 ohm resisters for bais adjustments. Should I add? Will it help? The worst thing I could do is chase my tail. I do beleive I'm on the right trail because I put one probe right across the speaker terminals and one on the bais supply. They match perfecly.
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