Fender "The Twin" noise in channel 2

[jose]

Hi, All. It is the first time I post a thread. I have found a lot of information in this forum and appreciate all people that share knowledge and spend their time to help .

I bought a Fender “The Twin” red knobs for twelve or fifteen years ago and it has been in the same place (music studio) all time, I never move it out. I have used it for 3 or 4 hours each Saturday afternoon; However last 6 month I did not use it. and last week when I turned on I detect a hum on channel 2 and it increase when I increase the gain. This happened only when the guitar is connected.


Characteristics:

The amp has a foot switch (two buttons) connected to change channels 1-2 and turn on/off the reverb.
The impedance switch is set to 16 ohms (two 8 ohms speaker serial connected)
I do not have any effects connected.
The guitar that is connected is a 2 humbuckers Telecaster (The guitar and cable does not produce any noise when connected to another amp).
The hum is not noticed when the standby switch is off.
The channel 1 is clean.

Schematic is here: http://www.ampwares.com/schematics/the_twin.pdf

I put off the chassis and clean with a brush a few dirty I found in there.
I cleaned the potentiometers with a spray.
I revised solder points and I saw it good (brighter).
The wiring looks good.

I replaced the tubes V1 (12Ax7) and V2 (12AX7) with news ones and cleaned sockets of all 11 tubes.
I checked the resistors (with a digital multimeter) on board for this channel ; apparently are good.
I did not remove any capacitor until now.

But the problem persist…….


I will thank to anybody who can help me.

Thank you.

[acorkos]

the input jacks on those amps have multiple switching functions, whether plugged or unplugged. one or more may be causing the noise. spray some contact cleaner into each and insert-remove-reinsert a guitar cable plug several times. also, they are susceptible to damage and one may be needing replacement. if you determine one of the jacks needs replacing, i would replace all of them.

http://musicpartsguru.com/closeup.as...d=321&offset=0

[jose]

Thanks Acorkos for reply.

I was busy last days, but Yesterday I returned to my Amp repairing.

I Cleaned and Checked all the input Jacks as you recommend and I could see the first Jack of channel 1 lost the inner metal ring and has its cover broken; then I connect the guitar in parallel mode in channel 2 (without using pedal switch) and I noticed a very small noise reduction but the initial failure persists so I come to check the first pre-amp (V1) again, replacing tube socket V1 and surprise of me, the high level noise disappear.

I thing the socket had a mechanical failure not detected at first sight.

Now only a very low Hum produced by the Transformer , noise that I think is normal.

And now that I have the chassis on my workbench the next step will be replace the input Jacks of channel 1 that are the most used.



Thank you again for you attention.