Roadster Issue

[Dilemma]

I recently purchased a Roadster Combo. The amp has suddenly developed a loud humming from the 1st and 2nd channels. Oddly enough the problem is nonexistent in channels 3 and 4. When I turn the reverb down or off? The hum vanishes.

Any idea what's happening here? Why only the two channels?

Any help will be greatly appreciated.

Thomas

 

[domct203]

I recently purchased a Roadster Combo. The amp has suddenly developed a loud humming from the 1st and 2nd channels. Oddly enough the problem is nonexistent in channels 3 and 4. When I turn the reverb down or off? The hum vanishes.

Any idea what's happening here? Why only the two channels?

Any help will be greatly appreciated.

Thomas

Each 12AX7 preamp is actually two tubes in one bottle, referred to as sides A & B.

The preamp tube function in the Roadster are:
V1A=1st Gain Stage
V1B=2nd Gain Stage

V2A=3rd Gain Stage channels 1 & 2
V2B=3rd Gain Stage channels 3 & 4

V3A=4th Gain Stage channels 3 & 4
V3B=Tone Stack Driver

V4A=Reverb Return
V4B=Reverb Send

V5A=FX Loop Send Buffer
V5B=FX Loop Return Buffer

V6A&B=Phase Inverter

Now, as you will see, one half of V2 will only effect channels 1 & 2, and the other half will only affect channels 3 & 4. It is quite possible that only one half of the tube is bad, giving you issues in only channels 1 & 2. I really don't know why the reverb level effects this though.

I would start with changing V2, and have another tube on hand for V4, just in case.

Good luck, be sure to post the results.

Dom

 

[Dilemma]

Started with V2. Problem solved!

Odd the tube map isn't in the owners manual, it on a placard inside the amp.
Also, you have to remove two power tubes to get your fat hand inside. :mrgreen:

Thanks for the tip BTW!