Hum adjustment

[Comity]

Hi All,
I have a question that may be obvious to the more experienced.  Should one do a hum adjustment each time the power tubes are changed out?  I recently noticed a hum in one channel of my Stereomour (previously masked by the crackling noises from having my WIFI router too close to the amp), and when I switched the power tubes the hum changed channels, so it is definitely tube related.  I have been using JJ's 2A3 tubes since about 2015, and the tube that has more hum appears to have a much darker glass support at the bottom of the tube compared to the non-humming tube. The glass support is almost black compared to the other tube in which the glass support is still clear.  This got me to wondering if I should have done a hum adjustment when I first installed the JJ's.  I did the hum adjustment when I built the Stereomour with the original Sovteks.  Also, would there be any reason to go back and do any resistance or voltage checks?  Those were all within normal range after I built the amp. Thanks for any input on this topic.

 

[Doc B]

Yes, you need to check the hum trim any time you change the tube.

 

[Comity]

Thanks Doc....I should have realized that.  Do you think that not adjusting the hum trim could have played a role in causing the tube to hum prematurely and also darken the glass support?

 

[Doc B]

Nope. You say the tube is 6 years old. That's a pretty healthy lifetime for a 2A3. Have you tried trimming out the hum on the tube in question? It certainly wouldn't hurt to do a voltage check to see if the tubes are drawing extra current from age.

 

[Comity]

Thanks Doc.  I appreciate your input and will go ahead and trim out the hum on the questionable tube and check voltages.  It's probably a good idea to go ahead and confirm everything is still in spec.

 

[Pkay]

Is it okay to trim the hum trim while the amplifier is connected to speakers.  ie, check the hum trim by ear rather than instruments?

 

[Paul Joppa]

Yes, it works quite well unless the hum is inaudible - in which case, you don't need to get it better  :^)