Fender Super Twin

[Reimer]

Hey There.

I have a Fender Super Twin 180watt, the tubes are new, caps new, but it have little vol, and there is some kind of octave/distortion on the notes. Anybody that can give me a clue on what could be wrong.

Best Regards

S

[Enzo]

First, look to see if the speaker is plugged into the right jack.

Connect the amp to some other speaker cab. Does that sound the same, or is it OK there? And of you can, connect the internal speaker to some other amplifier. Those tests are looking for a faulty speaker.

Turn the reverb up midway. Now rock the amp back and forth enough to crash the reverb springs.. Does that come out sounding the same weak way, or is the reverb noise loud?

The distortion switch is on the control, but it also runs through the distortion/boost footswitch jack, so make sure the jack contacts are working and that the switch on the control has continuity to ground.

Even with distortion turned off, does turning the distortion control affect the sound?

The schematic has voltages on it, so check them. Once inside the amp, before doing much else, use a smallscrewdriver or even yor meter probe, and touch pin 2 of V4 - that is the input to the power amp, the input to the phase inverter. Does touching result in a hum out the speaker?

V5 is a driver tube for the outputs, it should be a 12AT7, not 12AX7, so check that. Now, do you get B+ voltage on pins 3 and 4 of all power tubes? About 500v? And about -60v on all the grids at pins 5? Back to V5, you got about 395v on pins 1 and 6, and about 75v on pins 3 and 8? And back further to V4, got about 270v on pins 1 and 6, and about 85v on pins 3 and 8?

Likewise go stage by stage through the preamp and check voltages.

If all the DC voltages seem OK, then apply a strong steady signal to the input and trace it through the amp. A scope is best, but a signal tracer works well, or even an AC volt meter. How much signal voltage is present to the master volume control?

[Reimer]

Enzo you saved my day, you are the sunshine of my day, thanks alot

Silver

[greekie]

What was the problem? Just so the collective unconscious can absorb the solution and reach a higher rate of fixed Fender Super Twins ;-)

[Reimer]

It was some bad soldering in the phase inverter Circuit. I thought I have checket and done them all, but apparently I missed some

[Jazz P Bass]

Not surprising, as those amps are a snake pit.

[Reimer]

Thatīs the right description, maaaaan It have been some stressful and frustrated hours servicing this amp, but Enzo was so talented and gave me good information, and that made med look at the phase inverter and vola the problem solved