Twin Reverb 65 Reissue scratchy volume 1 and 2 potentiometers and other issues

[jalexquijano]

My Fender Twin Reverb 65 Reissue is rarely used and now that i started using it i have noticed the following:

1. Scratchy 2nd channel Volume Potentiometer when wiped. It does the same on the Channel 1 but not as harsh as on Channel 2.

2. Random noise while playing

3. Reverb is very sensitive and sometimes it sounds more as vibrato than reverb. I only dial it to 1.

This amp is a reissue which is PCB and not point to point as the originals of the 60īs .

What can i get this sorted out and fixed by myself?

[The Dude]

I'd try tube substitution first. Is the random noise hum, popping/clicking, etc.? You could have a tube arcing. The pots could have DC on them (easy enough to check with a meter), or they could just be noisy pots in need of cleaning or replacement. Try cleaning them first. Troubleshooting is the same process whether its a PCB or point to point.

[jalexquijano]

its crackling noise. how do you check DC on the pots? I will try cleaning them with DEOXIT fader lube:

https://www.amazon.com/Hosa-F5S-H6-D.../dp/B00006LVF1

[jalexquijano]

Problem fixed. Sprayed some deoxit fader lube on both volume pots and reverb pot and viola no more scratchy noise!

[nevetslab]

Rarely does a week go by without a Fender Twin Reverb come in with various isseus. Sometimes it's scarry noies, all from the front panel PCB assy usually. Most of the amps thru my shop come in road cases, so they live a hard life. On a good day, the chassis will come out of the cabinet without its' beveled front grabbing hold of the loose adhesive foil that's suppose to be bonded to the inside top of the cabinet. On bad days, the chiesl-like panel grabs the loose front flap and begins rolling it up while you're trying to slide the chassis out, stopping it dead in it's tracks. Then you have to remove the speaker baffle to have a chance at getting the chassis out without further damage. Of course you have to remove the reverb tank and the lower rear panel to get at the baffle screws. And then restore the damage to the rolled-up foil. Grrrrr!

Invariably there are several gritty pots, as well as broken solder joints on the pots' solder tabs, as well as the mechanical support bracket tabs. I usually un-solder the pot from the PCB, then unfold the cover tabs to remove the cover, and brush on Caig DeOxit onto the resistive track and exercise it. I think I've only found a couple times where there was DC leakage from the plate circuit of the preceding stage coming thru onto the pots. While I have the PCB out, I'm also looking for all solder fractures. The stock PCB mount input jacks are known to go bad, and when they do, I remove them and install open frame Switchcraft jacks (Type 12A or L12A and wired them in, ending any further jack issues. And, often find solder fractures on the ribbon cables that connect this ling skinny board to the main PCB

On some Twins, Ive had to outright replace the Volume pots, as just touching it would evoke loud scary noises out of the amp, or pounding on the top of the amp.

Microphonic input tubes V1 & V2, as well as V4 are common. As the amp ages, tube socket pin tension gets to be an issue. Sometimes I can re-tension them with a very tiny jeweler's screwdriver, if not, replace the socket. Another problem that finally occurs is where Fender's change in their Solder Masking on the solder pads for the tube socket wires have not allowed enough solder to bond from the solder pad and the pin wire. Why some bean counter trying to save a few ounces of solder in the flow solder machines over a 1000 PCB's thought it would be a good idea to reduce the size of the solder mask on the solder pads is beyond me. A real pain to have to lift up the main PCB, and, one connection at a time, un-solder the pin wire, scrape away all the solder mask to then re-tin the full solder pad, and then re-install the wire, now having all the solder pad surface to wick up the solder from it onto the wire. But, the operation (on all six preamp tubes) did cure several obstinate Twin Reverb amps.

All in a day's life servicing Fender Twin's.

[nosaj]

Rarely does a week go by without a Fender Twin Reverb come in with various isseus. Sometimes it's scarry noies, all from the front panel PCB assy usually. Most of the amps thru my shop come in road cases, so they live a hard life. On a good day, the chassis will come out of the cabinet without its' beveled front grabbing hold of the loose adhesive foil that's suppose to be bonded to the inside top of the cabinet. On bad days, the chiesl-like panel grabs the loose front flap and begins rolling it up while you're trying to slide the chassis out, stopping it dead in it's tracks. Then you have to remove the speaker baffle to have a chance at getting the chassis out without further damage. Of course you have to remove the reverb tank and the lower rear panel to get at the baffle screws. And then restore the damage to the rolled-up foil. Grrrrr!

Invariably there are several gritty pots, as well as broken solder joints on the pots' solder tabs, as well as the mechanical support bracket tabs. I usually un-solder the pot from the PCB, then unfold the cover tabs to remove the cover, and brush on Caig DeOxit onto the resistive track and exercise it. I think I've only found a couple times where there was DC leakage from the plate circuit of the preceding stage coming thru onto the pots. While I have the PCB out, I'm also looking for all solder fractures. The stock PCB mount input jacks are known to go bad, and when they do, I remove them and install open frame Switchcraft jacks (Type 12A or L12A and wired them in, ending any further jack issues. And, often find solder fractures on the ribbon cables that connect this ling skinny board to the main PCB

On some Twins, Ive had to outright replace the Volume pots, as just touching it would evoke loud scary noises out of the amp, or pounding on the top of the amp.

Microphonic input tubes V1 & V2, as well as V4 are common. As the amp ages, tube socket pin tension gets to be an issue. Sometimes I can re-tension them with a very tiny jeweler's screwdriver, if not, replace the socket. Another problem that finally occurs is where Fender's change in their Solder Masking on the solder pads for the tube socket wires have not allowed enough solder to bond from the solder pad and the pin wire. Why some bean counter trying to save a few ounces of solder in the flow solder machines over a 1000 PCB's thought it would be a good idea to reduce the size of the solder mask on the solder pads is beyond me. A real pain to have to lift up the main PCB, and, one connection at a time, un-solder the pin wire, scrape away all the solder mask to then re-tin the full solder pad, and then re-install the wire, now having all the solder pad surface to wick up the solder from it onto the wire. But, the operation (on all six preamp tubes) did cure several obstinate Twin Reverb amps.

All in a day's life servicing Fender Twin's.

It's so good to see your well detailed posts on the amps you work on.

Nosaj

[jalexquijano]

Nicee write up. Anyway, even though both volume pot scratching went away after spraying deoxit fader lube inside them, the amp does experience a loud hum when coming out of standby mode which lasts almost 1 minute and then it settles down. It also produces some random cracking noise during play time like an old vinyl record. I did noticed that if i tap the first preamp tube located to the right it sounds as you were tapping to a microphone. Should in retension and clean each socket. Bought this amp used in 2010.

[Randall]

"I did noticed that if i tap the first preamp tube located to the right it sounds as you were tapping to a microphone. Should in retension and clean each socket.

That is a microphonic tube, it needs to be replaced or swapped with the vibrato tube. Might be where the "random crackling noise" is coming from.

[catalin gramada]

That.'s a current issue using old pots as grid reference.Put 1M in parallel with the wiper to see if scratch is gone

[capacitivewaves]

Hi, I'm new here and experiencing a similar problem on a client's 65 Twin Reverb : both volume pots are scratchy. Cleaning them with deoxit didn't help, then I removed the bright caps in case they were leaky and it went worse, then I changed the pots and the shared cathode bypass cap on V1B and V2B and the scratch is still here. I am quite running out of ideas here.

That.'s a current issue using old pots as grid reference.Put 1M in parallel with the wiper to see if scratch is gone

Catalin gramada, do you mean a 1M from wiper to ground ? thanks

[pdf64]

Yes.
You haven't mentioned subbing in known good 12AX7, ie tubes with low grid current, for V1 and V2?
Some tubes, perhaps whole batches of modern production, have excessive grid current, which causes such issues if there are pots in the grid leak return.
Always remember that it is inherent that the most unreliable, problematic things in a tube device are the tubes / the connections to them.

[capacitivewaves]

You haven't mentioned subbing in known good 12AX7, ie tubes with low grid current, for V1 and V2?

I did change them, they were microphonic. I will try others though, just to be sure, and try adding those 1M resistors. Thank you