Buzzing on tube amp

guitarboy2828

So, I bought a Marshall Haze 40. It's been taken out of a combo cab, I just have the chassis/amp part, not the cab/speaker.

So, I'm running it into a 1x12 cab. When I turn it on, it hums/buzzes LOUDLY. If i gently tap the pc board it stops, then crackles then starts again. A few minutes later, it's silent and tapping the board does nothing, it stays nice and quiet.

I find this super weird. My other marshal head doesn't need any sort of warm up time, so, I can't imagine this is the case, unless because of all the digital components it's causing issues?

What could be causing this? Bad tubes? Filter caps? Bias problem?

Stoffeltoo

Prbably tubes and caps. Had a JTM 60 that did the same but sounding harmonic when bumped/ slapped or played above certain volume. Tubes replaced, serviced and problem solved.

petercornell

Paul

I would also suggest a faulty solder joint. How old is the amp? Does it become faulty if you tap in a certain place on the PCB?

The heat in a valve amp can make the solder crystallise and become brittle. The older the amp, the more often this occurs.

When the amp is turned on, the joint is not making good contact. As it warms up, the solder expands and makes contact.

Tapping can also make the solder joint good or bad.

Could also be a dodgy valve as mentioned above......

Those are the 2 most common causes.

Peter

guitarboy2828

petercornell wrote: Paul

I would also suggest a faulty solder joint. How old is the amp? Does it become faulty if you tap in a certain place on the PCB?

The heat in a valve amp can make the solder crystallise and become brittle. The older the amp, the more often this occurs.

When the amp is turned on, the joint is not making good contact. As it warms up, the solder expands and makes contact.

Tapping can also make the solder joint good or bad.

Could also be a dodgy valve as mentioned above......

Those are the 2 most common causes.

Peter

Thanks for the input Peter! The amp is fairly new actually, couple years old at most. I did look for dodgy solder joints, but, usually hard to see. It is on the ecc83 sockets that it is dodgy, so it may very well be a bad solder joint.

I'm thinking it could also be a bad cap?