Hi All,
Speakers installed - no source attached.
Just installed tubes (including el84m) and powered up. After tubes warmed up (10 secs?) I get deep hum then loud feedback whistle...no smoke.
I tried twice and quickly unplugged. I had my meter attached to read bias the second time and noticed the bias voltage go up way pass .35 mv -i was unplugging and it got to .80!!! it might have kept going... I used the zener option - no other mods.
This weekend I will start looking for the simple stuff -but I wondered if anyone had advice where to start? My previous builds have either worked or had no sound- so this is scary and I hope I didn't fry my brand new el84m's. Would a bad 12au7 ( i used a unproven NOS RCA) cause this?
Thanks,
Mark