Caliber .50+ Hum

[peterhocking]

Hi everyone

My Caliber 50+ has developed a hum in the clean channel, I haven't tested the overdrive channel yet.

Changing the power valves hasn't fixed it. Is it likely to be one of the preamp tubes? If so, any particular suggestions as to which one?

TIA

Peter

 

[MesaBodgie]

I would suggest you have the board checked for cold solder joints.
Some of those resistors carry big currents so they and the solder joints get hot.

 

[Monsta-Tone]

The easiest place to start would be the preamp tubes. Mainly, V2, 3, 4, 5.
If the hum is not in the lead channel, then I wouldn't worry about V1 since it is dedicated to the lead channel only.

If this doesn't fix it (swapping in a known to be good tube 1 at a time), then I would say it is most likely filter caps.
I've seen a number of the .50 Calibers start humming within the last few years.
So much for the argument that filter caps will last forever!

It's an easy fix if that is the case, but try the tubes 1st.

 

[MesaBodgie]

I had a major hum issue with my 50 cal + years ago and on inspection I found that one of the 2 watt resistors had been mounted vertically in the PCB
at a height of about an 1/8". The heat from the resistor screwed the solder joint.
I remounted it horizontally and added a piece of similar OD wire to patch so as to keep the heat away from the board.

Might not be your problem but a big change in hum with my amp.

You would think that MB's QC would have figured out that mounting a heat carrying resistor so close to the board
would be asking for probs.
I'd call it a design fault.

 

[Monsta-Tone]

Definitely not one of their better ideas! Every .50 Caliber I've seen has burn marks on the board right there!