Dual Rect Popping/Crackling Noise (Video Sample Included)

[loddie]

I just picked up a used Dual Rectifier and cab and was hoping you guys could tell me what this noise is. Here's what a I know: the amp will make this noise on and off at random intervals, generally starting a minute or so after turning it on. It does this with or without the guitar plugged in (as shown in the video). I can impact the sound or even make it stop for a while by giving a nice tap to the side of the head, however I did not do this in the video, it stops and starts on its own.

Here's a link to the video: http://www.youtube.com/watch?v=3q482tvDxHs

 

[JCDenton6]

Sounds like a preamp tube going microphonic, I'd lightly tap on each one with a pencil to find the culprit, then swap it out.

 

[loddie]

So I tried that on the preamp tubes and found nothing, but did the same to the power tubes and found that the second from the left seemed to be the culprit. I've read that you can run the amp at 50w by removing two power tubes and a rectifier tube and plugging the 8ohm cab into the 4ohm output, would this be a safe way of confirming that the second tube is the entire cause of the issue?

 

[bendo]

You'll be fine running the amp that way. It is fully supported.

However, that noise is likely your power tubes. Especially if present on both channels.

 

[Casper]

I have the same issue with my Blue Angel...I believe its a bad pot (mine is volume)..its at my tech's getting looked at. Will report back..