Hot Rod Dlx Fizzy artifact!

[Mike62Jazz]

My MIM Hrd developed a fizzy sounding artifact while playing A note on the 12th fret A string. After hitting that note, especially, I hear an after-effect fizz or buzz. I had a friend over to play that note and I tried to find the cause. It seemed when I moved the reverb tank around in the bag, I was able to stop or minimize the sound. BTW, is the reverb tank supposed to slide around in the bag and not be screwed to the cab? The reverb is held down by 2 screws holding the bag to the floor of the cab and is sitting on a piece of cardboard! I t doesn't seem to be a cabinet vibration of any sort. I believe it's coming through the speaker as the note decays.

[Jazz P Bass]

Fender HRD

If you really want to prove it out, try to run to amp into another speaker.
You could also try to tap the preamp tubes with a pencil to see if any are microphonic.
On these amps i have found:
Loose screws, microphonic tubes, bad solder joints.
The best one was the indicator lamp being offset in it's holder. The lamp was rattling against the holder. I just rebent the holder.
Happy Hunting!

[pecorporation]

Verify it's not the speaker. Plug in an external speaker and run it with the internal and see if the external speaker has the same "fizz". If it doesn't, then try tightening speaker mount screws, sometimes they loosen and vibrate against the sound board.

If problem persists, try swapping out tubes, one at a time.

Anything else would be internal. I've seen loose plugs, aside from failing solder connections, on crimped wire ends that just 'set' on the pc board terminals and vibrate with speaker causing strange noises.

[Mike62Jazz]

It appears to have been a NOS 5751 in V1. It made a bunch of crackling noise when tapped. May be bad or needs the pins cleaned. Switched in another NOS 5751 and all is good. Thanks for the replies.

[Jazz P Bass]

5751 triode

Nice job on the repair.
And thankyou for letting everyone know that the issue was resolved.
So many times posts just poof! and you never know if you where any help.
That 5751 is a new one for me.
Sounds like a cool tube.
High mu.
Thanks
John G

[Mike62Jazz]

Well, I jumped the gun on the fix! The tube change made it a little better, but I hooked the speaker from my Blues Jr to the Hot Rod and there is no fizz. I tried tightening the screws holding the speaker (they were a little loose) but that didn't fix it. I do have another identical speaker that I took out of the Blues Jr. when I put in a Eminence Red, White, and Blues. I may switch them out this weekend and see if it goes away completely. It's also a good excuse to maybe upgrade the speaker

[chipprogr]

i think youve still got a microphonic tube somewhere and the air pressure vibrations from the speaker are setting it off. Some tube microphonics are severe with only certain notes played on a guitar. Changing your speaker wont help. Keep us informed-Eric

[Mike62Jazz]

Well, after much scrutinizing,chopsticking, preamp tube swapping, etc., it appears to be the power tubes! I had a set of GT 6l6Ge (rated 7) in there biased at 70 for about a year now. As a last resort, I put back the original GT 6l6GB (Blue rating) power tubes. The artifact appears to be gone. There is no after-effect ghost note. I should have figured it may have been in the power section earlier when I plugged in to the power-in jack of the effects loop and the problem was still there. I believe that doing this removes the preamp from the equation. I had to rebias to 68 and everything appears to be good.
I am a little disappointed that the 6L6GE only lasted a year(especially since they only have 3-4 hours on them) , but at least I found it and learned a few things along the way. Thanks for your replies and suggestions.

Mike