Lower volume from right channel

About a week ago while playing my custom-made push-pull EL34 amp I noticed a sudden spark coming from the bottom of the amp toward the back. I immediately turned the amp off. A few minutes later I bravely turned the amp back on and surprisingly it continued to play music. However, I've noticed the balance has been off since experiencing this. The left channel appears louder, with greater presence. Can anyone diagnose what the problem could possibly be before I have  a tech look at it. Thanks for your feedback!
Swap the tubes and see if the right channel is louder. If so then it is a bad tube!
I agree with yogiboy.  Since it's a custom made amp, the designer might be using a fuse or resistor that might have popped when the spark hit.  If so, that would need to be replaced.  Normally if something like that happens, the amp wouldn't work on that channel, but it would depend on the topology of the amp design and how it's implemented.
Thanks for your feedback. I will try swapping tubes and let you know the results.

I would look for a blown EL34 tube screen resistor. Should be easy to see.


Follow pin 1 on each right channel EL34 tube for the resistor for each tube.


Bias is way off.

Tube shorted.

Possibly a bad driver tube.

How many hours do you have on the power tubes? Average life, I believe, is about 2000 hours.

I swapped the tubes but found the situation to be the same. I'll have a tech check the above possible causes. Thanks for the feedback gentlemen!