Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: peteys123 on February 03, 2019, 09:54:22 am

Title: 67 princeton reverb hum
Post by: peteys123 on February 03, 2019, 09:54:22 am

  I'm getting some hum on my princeton reverb  with a new CE cap installed. I'm getting 32V of ac on the triangle symbol of the can cap. Could this be the cause of hum?   It doesn't hum if I pull the phase inverter tube V4 ,  so I was thinking it may be a bad can cap?  Or grounding issue?

Title: Re: 67 princeton reverb hum
Post by: sluckey on February 03, 2019, 10:18:04 am

32vac is too much. Probably a dried up can. Try this... Use some gator clips to connect another cap between ground and the suspect cap. If hun improves you got the culprit. If not, look somewhere else. BTW, which circuit is fed from your triangle cap?

Title: Re: 67 princeton reverb hum
Post by: peteys123 on February 03, 2019, 10:51:09 am

That's what I thought.   It's a new cap though.   From the AA1164 layout, it goes to 2 separate 18k resistors.  I just checked my other PR which doesn't hum and I'm getting 28vac at the triangle and sometimes .997 vac, so something is not reading right?