fender tiwn

[amptech]

Hi all,

Has any one had this problem with a fender tiwn valve amp befor!

the problem is after rechecking the pcb for damage and revalving the beast and powering up and this happens.....
low hum, and low volume gain on both channel's!

I would be very greatfull if someone came across this fault and could shead some light on this matter.

Thanks for now
amptech.

[MWJB]

How low? Were there any strange symptoms before revalving (unwanted distortion, low out put?). It's quite common for PI plate load resistors to burn open in these amps, too much plate current can cause hum, are all screen grid resistors in good order...these are the first things I'd check.

[amptech]

fender tiwn

Hi,

There's bad distortion when you plug a guitar signal in and try truning up the gain's. all grid resistors have been replaced with 470 ohm 3w types and the filer cap's checked on the psu board all good there.
the only thing is there's a low leave hum no matter how high the gain/volume is.....
any help with this matter would be greatful.

thanks.
wayne.

[MWJB]

OK, so now check plate voltages at the PI tube.

Check 6L6 plate current.

Check the condition of the 100ohm filament to ground resistors.

[52 Bill]

What model Twin is this? Re-issue or old style. And I assume this is a Fender Twin Reverb?

Even though you have replaced all of the tubes, it is possible that one of the new tubes is bad.

Like MWJB sez, check the power supply voltages.

[amptech]

fender tiwn reverb mk2

What model Twin is this? Re-issue or old style. And I assume this is a Fender Twin Reverb?

Even though you have replaced all of the tubes, it is possible that one of the new tubes is bad.

Like MWJB sez, check the power supply voltages.

Hi there,

All valves were test via fitteing them in to a working amp and all was well.
even 47 ohm resistors in the power supply unit that sets the hum balance are ok and all voltages using the diagram are correct.
and yet things are still not right.....
any help would be great, cheers for now.

[MWJB]

"all voltages using the diagram are correct" ALL voltages? What are they then? It's not that I don't believe you..it's just ...OK, I don't believe you.

Please list plate, screen grid & grid voltages for 6L6s (pins 3, 4 & 5) and plate & cathode voltages for 12AT/X7s (pins 1, 6, 3 & 8). If the problem affects both channels it's most likely around the PI & power amp.

[amptech]

fender tiwn

Hi all

found the little git that was making this fault 'r' 146 is a 90k , it was o/c and quick replacement was fitted with overal good clean sound with signal pluged in.
the next problem with this amp is the reverb is not working correctly so back to the drawing board and see what's what!

A 'big' thanks to you all for your help and advice with this nagging problem.

many thanks

Amptech