Roadster Crackling/Popping sound in Channel 1 Tweed Mode

[dgandalf]

Hey,

I have a Roadster amp with sound issue. This sound issue only occur when I set channel 1 on tweed mode it gets crackling/popping sounds after a minute or two staying on that channel. I am think its a tube issue, but I just cannt figure out which tube causing the problem.

I've tried swapping the pre-amp tube on position V2 with a new tube as it stated in the manual as "3rd Gain Stage CH1/CH 2" which sound the case but appears not.

Any idea how to fix it?

Thanks!

 

[bandit2013]

I would experiment with a good Mesa 12AX7 and roll the tube though V1 to you run out of options. If you have other brand of tubes in the amp, be weary of the V3 and V5 positions as they have a cathode follower circuit on half of the tube. There is a change of plate voltage that is applied to the preamp tubes for each mode and channel in order to obtain different gain character and tone. The noisy tube is also used in the other channels but is driven differently and may not cause the same issue. Tube roll would be the only way to isolate which tube is at fault with particular channel voice. Eventually, it may become apparent with the other channels.