Hi,
Well, I just acquired a Vox AC50CPH. All was working, checked bias for EL 34 which was close to 38mv on each valve. Fine tuned it and enjoyed the amp for a day.
Then, I decided to try my Marshall VM2266 KT66 output valves in there. Placed them in, checked for bias and for as much as I wanted, I couldn´t reduce them below 60mv, so as I coudln´t properly adjust them, I removed them. (Pitty, because they sounded great....)
When I was going to put back my EL34, I didn´t notice that one of them had the base plastic "guide" broken. So, as I felt it was going down, I just inserted it.
When I turned on the amp, I sudeenly heard some "hum" (half a second), and then.... silence. The "green light" from the standby switch didn´t light.
HT Fuse blew.
I replaced the HT fuse with another of same reference (from the Marshall 2266), then, properly inserted the EL34 valve and the amp worked again. BUT...
- Both EL34 light up.
- I can hear my guitar.
- I am only able to adjust the left one to 38mv. The multimeter doesn´t erad anything at all in the right valve.
- I tried an other EL34 I had spare, even swapped their places, etc, etc. Both EL34 still light up, but I can never adjust the right valve bias.
Also, the multimeter doesn´t detect any resistance in the right potentiometer, reading from the probes. But It does for the left one.
What could this be ? Can anyone give me a hint ? If too complicated, I´ll send it to a tech.
Thanks !