Fender '65 RI Deluxe Reverb making noise

[retrorod]

I am having trouble figuring out the source of electric crackling noise on this amp. It has been re-tubed and biased. It sounds great mostly but when pushed hard with some volume will crackle like some solder joint is compromised. I have re-flowed most of the joints on the main pcb and 100% on the pot/jack board.
The noise is not present with the chassis removed so I am fairly certain that it is caused by vibration.
Any suggestions on isolating the offending area or where else to look?
Thanks for any ideas or encouragement stories.....I have been working on it for awhile.

[Enzo]

Hand wired sockets. Well I would SURELY check the solder on them.

Does the noise go away with ALL controls set to ZERO? Does ANY control have ANY effect WHATSOEVER on the sound - tone of it , volume, etc.

I'd go down the sockets and check voltages. Is there B+ present on pins 1 and 6 of all the small tubes?

The tube next to the power tubes is a 12AT7 phase inverter. Does removing that tube kill the noise?

[retrorod]

Let me be more specific. It does not make any noise while on or played lightly up to 2 or 3 on the volume, but if up to 4 or so and digging in with some lower notes or power chords, it gives a static crackle that goes away after the 'attack'.

[Enzo]

Well, in that case, I would surely check the solder on those hand wired sockets. And if you are missing the plate voltage on one side of the phase inverter, the class AB circuit will sound like crap on peaks.


Otherwise you may have a parasitic oscillation. One thing to do is to work with lead dress, in particular power tube leads - keep them away from preamp tube wires. And try to keep grid wires away from plate wires.

If you think it is vibration and are sure the speaker is OK, then with the amp all assembled, power it up, ball up your fist, and whack the top of the amp hard. Does that create the noise? The amp SHOULD sit there in silence when whacked. Any noise is a loose connection of some sort.

[retrorod]

Thanks much Enzo, I will proceed with your advice this afternoon after work and report back!

[ReadyTeddy]

IF you have a scope, connect it to the amp's output and see if you can visually see the static crackle. If you can, go through the amp stage by stage with the scope until you find the stage at which the noise appears. That way you'll narrow down the area to concentrate on. Also, while you're going through the amp with the scope, either using the scope or a DMM check DC voltages on all stages to see if they are within a reasonable range. Also, all of Enzo's suggestions are excellent.

[Aloha_Mark]

These intermittent problems are terribly annoying. Mine is on a 1965 Vibrolux Reverb Amp which has a shot of galactic noise and crackling for 20 seconds or so, and then goes away for minutes. All volume pots are at zero. How do you troubleshoot a problem like this? One tech suggested swapping out the preamp tubes, but once I pop the chassis, I'd like to have all the parts I need to fix/repair, and since I don't, I keep putting off the testing. And since I don't have a storage scope (which would be useful for selective monitoring), that's another reason I procrastinate. That might help with Retro's problem assuming he could get a probe clip into each part of the circuit during a whack test. I am surprised that a modern RI amp would have issues people normally ascribe to vintage.

[pdf64]

'ball up your fist, and whack the top of the amp hard. Does that create the noise? The amp SHOULD sit there in silence when whacked. Any noise is a loose connection of some sort'
By combining the above test with the strategic removal of pre-amp tubes, it may be possible to close in on the problem area; no storage scope required.

'I have re-flowed most of the joints on the main pcb and 100% on the pot/jack board.'
The old solder needs removing from the joint, to ensure that flux gets to the component leads.

'I am surprised that a modern RI amp would have issues people normally ascribe to vintage.'
Presumably it's lasted past its 5 year warranty period, so as far as the manufacturer is concerned, it's vintage.
Pete

[Jazz P Bass]

Not sure if this was covered but did you try a different speaker?

[Aloha_Mark]

After collecting together all the parts to service the VR, I began tap testing with the chassis still attached to the cabinet. The rap to the cabinet replicated the noise pattern. Then, by tapping each tube, the culprit was the first 12AT7 next to the power tubes. I pulled the 12AT7 and plopped it into a tube tester. Gm measured ok but it varied by 10% with time, and further tapping. It was an old RCA tube that was about to give up the ghost. If I were NASA, I would crack it open to inspect filament and plate aging. LOL. Putting in a replacement tube cured the snarly intermittent noise. Thanks to all the posters for their helpful suggestions. Table time is difficult to get in the house (wife always complains about me making a mess), so that is why I delayed pursuing this troubleshooting until all the ducks (parts & test equipment) were in a row.

I have a second question now and that pertains to finding a tube tester which would have spotted the demise of the 12AT7. A Triplett 3444A has an audio output to monitor noise and microphonics. Any other worthy testers?

Third question: who makes the best replacement sockets for vintage amps? Is everything sourced from China now?

[Enzo]

The amp is the best microphonics tester there is. WHile it is running, tap on each tube, microphonic ones will make noise.

[Aloha_Mark]

As a followup to this thread, I should mention two other problems that were uncovered in troubleshooting my BFVR, and which probably apply to other Fender vintage amps with a reverb tank. First the switch contacts on the vibrato/reverb pedal can develop a resistance that is not zero, when they are supposed to be closed. This affects the vibrato circuit which needs to be grounded to be active. For the reverb circuit, the connection has to be open to be active, and that leaves a dangling wire connected to a preamp tube, another source of noise. I discovered these two effects when I moved the amp off the bench into another room with higher EMI content. Solution: ground the RCA jack for the vibrato pedal and leave the reverb jack open. A 50 yr old pedal where the ground is not even connected on the vibrato side except through the shield of the reverb cable is a dumb design. In addition, the RCA plugs invariably are tarnished on the inside. I'll get a new pedal one day, but this was the quick and dirty solution. The second problem involved the reverb circuit. The cables connecting the tank to the reverb in and out jacks also had tarnish on the ground section of the RCA plugs. They are also a source of noise and hum. Amazingly, it mimics tube noise, or exacerbates some form of oscillation in the tubes. I would have liked to replace both cables, but the tank is bonded to the vinyl jacket. How is this possible? There is a rubbery substance inside that jacket which has melted in the Hawaii climate. Unless you live here, you may never have experienced the disintegration of rubber. Rather than deal with the gunk, I'll order a new reverb tank, but have to locate a jacket to match the old one.

[Tom Phillips]

Mark,
My approach is to restore rather than replace vintage amp parts when possible. I offer the following comments for your consideration.

...the switch contacts on the vibrato/reverb pedal can develop a resistance that is not zero, when they are supposed to be closed...

The switch can often be restored with a shot of contact cleaner and vigorous operation. If not, the switches themselves can be replaced inside the vintage footswitch retaining the value of the original footswitch case.

...Solution: ground the RCA jack for the vibrato pedal and leave the reverb jack open...

Leaving the reverb jack open is OK but permanently grounding the vibrato jack leaves the neon bulb in the light bug flashing continuously. The results in faster wearout of the bulb and accelerated darkening of the bulb glass which reduces the tremolo intensity. An alternate solution is to use the reverb section of the footswitch to control the tremolo. A plus is not having to listen to continuous tremolo oscillator ticking if your amp has that issue.

...The cables connecting the tank to the reverb in and out jacks also had tarnish on the ground section of the RCA plugs...

Those plugs and those on the footswitch can be cleaned up with deoxit and a little twisting in the jacks. Sometimes the sleeve ears need a little squeeze with pliers if they are loose. Clean the center contacts of the plug and socket too and re-tension if necessary.

...the tank is bonded to the vinyl jacket. How is this possible? There is a rubbery substance inside that jacket which has melted in the Hawaii climate. Unless you live here, you may never have experienced the disintegration of rubber. Rather than deal with the gunk, I'll order a new reverb tank, but have to locate a jacket to match the old one.

Another opportunity to save your original parts. Especially the reverb tank since many people complain about how the modern replacements sound. The old style rubber weather strip that Fender put on top if the tank has deteriorated. Yours sounds like an extreme case but it happens in California too. You can heat up the top of the bag with a hair dryer to soften the rubber and then pull the tank out. Solvent will remove it from the top of the metal tank case. Then I’d warm the bag and turn it inside out. You could then scrape off the excess and cover what’s left with some material that won’t let the remainder bleed through. You could also just order a new tank bag but be aware that many of the replacements are thin single layer units rather than the double layer heavy tolex that Fender originally used.

Cheers,
Tom