2. amps-preamps
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What might cause LOUD hum in a Conrad Johnson pv6

The PV6 today blared out a loud hum after it had been running fine for a couple of hours. I shut off all power to the amp, pre-amp, tuner etc. I noticed when I moved the preamp that one of the output cables was disconnected.
I don't know if it somehow disconnected and it caused a hum or became disconnected when I moved the pre-amp. In anycase, I later plugged the cables back in securely and used only a tuner STILL A HUM then a turntable and STILL A HUM.

I am looking for someone who might have an idea what is causing the hum. I opened the preamp No smell all tubes appear to be working. So I am puzzled.
randall
randallvar
randallvar OP
1 posts
 
Thanks for your help and the quick responses. I sent the preamp to conrad johnson. The tech thought it might be a capacitor. The hum was in both channels coming thru the speakers. When I get the report I will post it for it might be a help to others.
mrmitch
359 posts
 
Randallvar, I had a CJ PV-5 which had a similar hum. Sent it to Conrad Johnson where they replaced some capacitors a nd the power supply. Sounds better now than when it was new.--Mrmitch
rogerbent
2 posts
 
Loud him in mine was a bad 40 MF section of main power supply dual filter capacitor. Antique Electronics has a CE Manufacturing 40/20/20 MF, 500v can that will work fine. You will need to drill additional hole in circuit board, but it fits fine. It is 2 1/2" tall. Original is 2" tall. New one fits fine.
johnsonwu
467 posts
 
One RCA socket lost ground from the cable yanking. Love the tube dampers. Add heat and cause users to buy lots of replacement tubes:)
rogerbent
2 posts
 
Even after replacing filter caps, I had hum even with the volume turned down. I swapped tubes. No change. I checked voltages on the zener diode string and each was reading 36 volts instead of 33 volts. The regulator transistors Q2 & Q3 were bad. I used a MJE15032G for Q2 and MPSA42G for Q3. I replaced Q1 also with MPSA93G though it checked ok. Quiet as a mouse now! Ground rings on many jacks are bad. Next job is replacing them with jacks with nuts on inside of jack panel.
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