Mark III combo reverb hum

[yoshman]

I have a Mark III combo (blue stripe) with a hum problem. I have narrrowed it down to the reverb knob. When i turn it down to 0 and gets louder as you turn it to 10. It does hum even if the reverb wire is not attached to the amp

Any help would be much appreciated.

 

[Lesgoldy]

Try replacing the reverb tube.

 

[yoshman]

Swaped out all the preamp tubes - sorry, i should have added that info.
Also the noise only happens with the reverb/master switch.
If i put the master switch to 10 - no noise.
If i put the master switch to (1-10) + reverb switch on (1-10) - there is noise.

 

[yoshman]

One question for Mark III owners.

If you put the Master Switch to 5 and the Reverb to 5 - do you get humming?
The humming increases as you turn the reverb higher.

I was told by the guitar shop that sold me the Mark III - that this was a normal thing for the Mark III amps.
Could someone please check this out on their amp and let me know.
I would really appreciate it.

 

[Lesgoldy]

One question for Mark III owners.

If you put the Master Switch to 5 and the Reverb to 5 - do you get humming?
The humming increases as you turn the reverb higher.

I was told by the guitar shop that sold me the Mark III - that this was a normal thing for the Mark III amps.
Could someone please check this out on their amp and let me know.
I would really appreciate it.

No my MK III doesn't hum under those conditions.

The only time I had an issue with the reverb making noise, it turned out to be the RCA connection to the amp. I replaced the connector on the cable running from the reverb unit. It was fairly easy to figure out,... the untit hummed and when I fiddled with the connection I could get the humming to go away. Soldered a new RCA connector on the cable, problem solved.

 

[yoshman]

Thanks GTS - but the reverb hum happens even if the reverb tank is not connected to the head. I just got off the phone with Mesa Boggie and they said that the reverb circuit is noisy and that this could be normal. I just got this amp used so i do not know if this is normal - and the guy/shop i bought it from said that he never put the reverb volume over 3.5.
Everything else on the amp is quiet. Should i take it back to have them look at it or is this normal like Mesa said.