Fender 65 Deluxe Reverb RI Buzz/Hum when Vibrato is engaged

[KCman]

Schematic:
https://www.thetubestore.com/lib/the...-Schematic.pdf

First, a couple filter caps were bad. I replaced all of them.
Next, the vibrato didn't really seam to work until intensity was on about 4. I replaced the Opto. and while in there, I changed the two .01uf caps to .02uf to slow it down a bit. Thats when I noticed the hum. I thought it might be the new bug I put in, so I put the old one back in. It was still there, just not as much. That is because when the new Opto. was in, it worked better and made the hum stronger. Speed knob changes the hum, but intensity does not. Reverb knob adds hiss to it.

The owner did the mod where you remove R12 and run a jumper from R25 (to give reverb and Vibrato to both channels)

60 hum/buzz is coming through when vibrato is on. I started pulling tubes V1, V2, V3 no change. If I pull V4, it goes away. Also, While signal tracing, I found if I touch V5 pin 1(or components that are at the junction) It stops. Oh yeah, touch with the probe (not my finger heh) . I tried different tubes, re-soldering parts, moving the few wires, there are, around.

Also, If I touch V5 pins 2 and 7 it mostly goes away.

It worked putting a cap from V5 pin 1 to ground. Any ideas, or should I just go with that. And, if so, what value cap? I had a .047uf death cap from an old vibrolux I tried.

Thanks,
Kirk

[KCman]

Any idea or thoughts?

[The Dude]

Did these problems exist before work was done on the amp? I'm always suspect of mods being done improperly. My first step would be to double check that work. I'm assuming the mod is the one described on this page?

https://robrobinette.com/AB763_Modif...nel_Reverb_Mod

(Scroll down a bit for the 65 DRRI)

[KCman]

I'm not sure what happened to my post, i must have deleted it by accident but,

I checked his work and touched up his soldering. He said it worked fine for a long time before the filter cap went. I tested the new ones before installing.

Maybe he didn't notice it until I put the new bug in and made the vibrato work better?? I didn't, but now that I put the old one back in, I still hear it.

He did this mod:

https://www.premierguitar.com/articl...reverb-reissue

[KCman]

Some of the nose was in the Reverb circuit, which I cleaned up. The hum in the vibrato is all gone and sounds good to me with a plate bypass cap on V5a. I either used a 200 or 250pf, can't remember. Is that range fine?

[KCman]

Update:
It sounded good at my place, but when he took it and tried it, the noise was back.

This happened the first time, when I replaced the caps. So, back at my place again, this time it was a louder hum and the footswitch popped when pressed.

I opened the 1/4" plug and found the single wire (not the shielded) stripped back so far I couldn't see the insulator, it looked like another shield. I fixed that and problem solved. I asked him who worked on that cable and he said it came from Fender like that. It was a fairly new switch.

I was getting some noise without the footswitch. That was fixed with the plate resisters on V4, solder touch up and the vibrato qieted down alot with the bypass cap on plate V5a (I kept that, the vibrato is so quiet now, can't tell it's on).

I should have checked the footswitch sooner. I've read about noise and hum coming from the switch, but still overlooked it. I need to build a plug to turn on vibrato without the switch. That's on the to-do now.

[nevetslab]

Update:
It sounded good at my place, but when he took it and tried it, the noise was back.

This happened the first time, when I replaced the caps. So, back at my place again, this time it was a louder hum and the footswitch popped when pressed.

I opened the 1/4" plug and found the single wire (not the shielded) stripped back so far I couldn't see the insulator, it looked like another shield. I fixed that and problem solved. I asked him who worked on that cable and he said it came from Fender like that. It was a fairly new switch.

I was getting some noise without the footswitch. That was fixed with the plate resisters on V4, solder touch up and the vibrato qieted down alot with the bypass cap on plate V5a (I kept that, the vibrato is so quiet now, can't tell it's on).

I should have checked the footswitch sooner. I've read about noise and hum coming from the switch, but still overlooked it. I need to build a plug to turn on vibrato without the switch. That's on the to-do now.

The Switchcraft right angle TRS plug you had opened (has the two slotted head screws holding cover/strain relief in place) is a tricky assembly to get the two inner cables properly stripped, tinned and shield prep'd and tinned, then soldered into place so there's no excess shield strands to short the Ring terminal. The cable jacket, over time in use, will slip back out of the gripping ribs on the inside top/bottom of the steel housing. The normal cure for that is, with the cover plate removed, grab hold of the cable a couple feet back from the end, hold it tightly while pulling on the jacket and 'milk' that jacket towards the plug. There's enough play inside the jacket to slip it towards the end, where you can then re-mount the cover plate. Yes, preparing the cable ends for a proper fit is a PITA....just one of those tasks you learn to do. I'm surprised after the decades of Fender using that stupid cable, that they haven't replaced it with better cordage. NOPE.

[Randall]

I have seen a couple of footswitches bad from the Mexican factory. Both had the outer jacket cut into too deep down thru the inner wires causing shorts.

[nevetslab]

I have seen a couple of footswitches bad from the Mexican factory. Both had the outer jacket cut into too deep down thru the inner wires causing shorts.

Yup.....me too. With that cable, and that particular Switchcraft plug, I've seen all sorts of attempts to not start all over, trying to salvage a botched job. No short cuts on that plug & cable!