Bottlehead Forum

Bottlehead Kits => Stereomour II => Topic started by: jerryZ on May 21, 2021, 06:32:19 PM

Title: Have to adjust hum pot after touching 2A3 tube
Post by: jerryZ on May 21, 2021, 06:32:19 PM

I found today that after I touched the right 2A3 tube and changed it position slightly,  I can hear the hum noise from the right speaker, the hum pot had to be re-adjusted to bring down the noise.
Not a big deal but just wondering if it is really that sensitive? I had the hum pot adjusted before and both channel were very quiet.

Thanks

BTW, mine is version 1, I built it back in 2013, have been in love with it since..

Title: Re: Have to adjust hum pot after touching 2A3 tube
Post by: Paul Joppa on May 21, 2021, 06:49:44 PM

The socket contacts are not perfect, and a slight movement will make a slight change in the contact resistance. If you have not cleaned the tube pins and socket contacts lately, that's probably what happened.

Title: Re: Have to adjust hum pot after touching 2A3 tube
Post by: jerryZ on May 22, 2021, 05:41:04 AM

Quote from: Paul Joppa on May 21, 2021, 06:49:44 PM

The socket contacts are not perfect, and a slight movement will make a slight change in the contact resistance. If you have not cleaned the tube pins and socket contacts lately, that's probably what happened.

Thanks Paul, I should clean the pins and sockets, it has been in service for 8 years..

Title: Re: Have to adjust hum pot after touching 2A3 tube
Post by: Doc B. on May 22, 2021, 05:53:33 AM

Exercise the hum pot a bit too, by turning it back and forth several times. Then reset it to the point of lowest hum.

Title: Re: Have to adjust hum pot after touching 2A3 tube
Post by: johnsonad on May 22, 2021, 08:41:03 AM

Great advice as always DocB.  I do this with the cleaning of the RCA's semiannually and removing and reinserting the tubes a couple of times.