Volume spike

[jeff]

 I'm having a problem with one of my favorite homemade amps.

 I'll play for a little while then all of a sudden it sounds like someone turned the volume up for a split second then it returns to normal every once in a while. This happens randomly and I can't make it happen on command so it's hard for me to test and pin down what's causing it. I've tried different guitars and cords same result so I'm pretty sure it's the amp.
  What may cause a random spike in volume?(bad tube, cap, resistor, ground, etc.)
 Anyone else have a similar problem? What was the solution?
 Any suggestions on where to start looking for the cause or tests I could run?

Thanks
  Jeff

[John]

Take a good look at the grounding on any gain or volume pot. I think if the ground lifts for a split second (bad joint) it would be passing full signal.

[jeff]

Good idea
  Thanks
    Jeff

[SILVERGUN]

One technique I have used for finding intermittent issues is to use the min/max function on your dmm (found on some multimeters) to monitor voltages over a period of time at different points in the circuit, in order to rule out certain sections one at a time....
It basically records the readings on a continuous graph, and allows you to catch something that you would normally miss....
An  intermittent volume increase should very well be a direct reflection of a voltage increase that you will have to trace by clipping your meter leads onto different points along the path and leaving them connected while you play and "record" the evidence...
With any luck you'll be able to narrow it down from there....good luck and BE SAFE

http://www.fluke.com/Fluke/usen/community/fluke-news-plus/ArticleCategories/DMMs/Under-Used_Functions.htm