High pitch squeal and ripped speaker noise on Fender Red Knob Twin "The Twin"

[jalexquijano]

My 1990 Red knob twin developed a random high pitch squeal on the overdrive channel which tends to also produce a ripped speaker sound when the amp has warmed up after 45 minutes of playing. Could this be due to a microphonic 12ax7 in v7 or v1?? I also notice the amp lacks some treble on the overdrive channel to achieve the JCM 800 overdrive. Any clues?

[stereomonostereo]

Start with the preamp tubes. When the amp is turned on and turned up, tap them with the eraser end of a pencil and see if you get the noise

[nevetslab]

I just finished with one of our The Twin's here at CenterStaging. It had two microphonic tubes, which after doing some swapping to move them down-stream, I ended up with freash tubes on the two inputs (V7, V1). The power tubes were also microphonic on this amp....well, two of them were. I had to wait for a new quad set of matched tubes to arrive.

This amp, and the Twin Amp, being very similar in construction, have always seemed to be noisy and with a hum level that I've never found a cure for. This Red Knob The Twin I just finished with also had a tendency for the reverb to howl if you turned it up too much. Seems like too much gain in the return circuit. I still have one of these in the bone yard here in the shop, and if I ever get some time, I've been meaning to tear into that and see if I can't tame it.

[jalexquijano]

I dial the reverb between 4 and 5. No more than that. Yesterday i played the amp for 1 hour and did not noticed any high pitch squeal. I guess its and intermittent problem. I do have Brand new Groove tubes 6L6GE. However, the 5 12ax7 and 2 12at7 are not so new.

The hum in this amp is high compared to the twin reverb 65 reissue and if you play rhythm chords with a les paul or es335 its not as clean as playing either of these guitars on a twin reverb 65 reissue. I have both amps and can tell quite the difference in the clean channel with a humbucker pickup.

[g1]

When it squeals, turn down the reverb and see if the squeal stops.

[jalexquijano]

Start with the preamp tubes. When the amp is turned on and turned up, tap them with the eraser end of a pencil and see if you get the noise

What i am getting is a 5 seconds siren like sound with some crackle when the amp is warming up during the initial 45 minutes of playing. Its intermittent and its produced even without a guitar cable plugged in.