Modified 5E3 issue when moving pups selector

[FREYES_7]

Hello All,

I modified a mojotone 5E3 kit, changed 0.1 uf from each channel to 47nF in normal and 22nF in bright channel, added back up diodes to the 5Y3 socket, pre PI master volume, 3 way switched feedback and added screen resistors to the 6V6s,

Most of master robinette's mods, it sounds great, no noises, the cables from the Master volume and 3 way switch NFB are shielded accordingly, but,,,

I was test playing the amp, and changed from neck pup to bridge pup quickly, and the volume oscillated for a while in the amp, like 5 or 10 seconds.  After that it stabilizes and goes back to normal.

Any clue on what might be happening?

Using a PRS Paul's guitar

[BrianS]

can you make the amp "oscillate" by doing something like unplugging the guitar, or plugging it in when the volume on the amp is up...to make a nice POP?  Or what about smacking the pickup with a screwdriver or something...will that make the amp oscillate?  What I'm thinking is some loud, non-musical "noise" coming from your guitar is revealing some microphonic component or connection inside the amp...?

[dogburn]

Also, did you modify the kit as you were building it, or did you build it first and then modify it? If the latter, I assume it all worked fine.

And of course, did you try a different guitar and different cable to rule those out?

[AlNewman]

Does the 5e3 have a feedback loop?  Do you have a schematic and some pictures?