Troubleshooting help - odd, intermittent problem

[kleinm]

I've had my amp up and running flawlessly for the last 2 or so months. Its a BN D'Lite with a handful of mods. Nothing major, however.

Well, within the last week, I've been getting a strange electric interference/raygun type noise when I play. If I'm not playing, there's no noise. It sounds sort of like electrical interference. It's most prominent with hard pick attacks, or if I vibrato a long note. As it trails off, it will sometimes do this noise.

Yesterday, I was showing the amp to some friends, and the output dropped to a whisper, and was replaced with loud static. Same on both channels. The guitar signal came through, but it was extremely quiet, especially compared to the white noise background.

Well, today I was probing around, and chopsticks didn't reveal anything. I decided to check my voltages, and as soon as I touched my positive probe to B+1, the static went away. Guitar signal back. I checked and reflowed the joints, and everything seemed okay.

A few minutes later, nothing but static. I touched B+3 this time, and it fixed it again.

As I was playing later, the odd intermittent noise came back.

I've tried swapping tubes, checked all grounds...and I can't seem to get to the root of it. Nothing consistently fixes it. Since both problems are intermittent, it makes it very hard to figure out what's going on....

Does anyone have any advice?

Thanks!
- mk

[bnwitt]

It diffently sounds like a bad solder joint or connection and it could be B+, ground or any thing else in the signal path. I hate to say this. but I would discharge the amp and check every single joint and connection. The last time I had this happen it turned out to be a wire going from a plate resistor on the board to a preamp tube plate pin. The wire was wrapped around the turret at the plate resistor point on the board, but I had never soldered it. The amp was fine that way for months. When I found it, I couldn't believe it had worked at all.

[mlp-mx6]

I've had similar effects when my bias connections were not solid. Once the ground was not soldered and another time the pot itself went bad.

[kleinm]

Thanks guys. All the joints *appear* fine, but I should probably reflow every single solder joint, as has been mentioned. This has been a tough one to pinpoint!

[kleinm]

Question - how does an amp behave if a tube socket is arcing internally?

The reason I ask is the sound is very "electric", for a lack of a better word. When I built the amp, I remember fearing the socket pins wicked a lot of solder (bad pin-soldering technique initially). After a bit, I got the hang of it, but there were some that really felt like solder just ran down the pin....

*grasping at straws*

[heisthl]

Always put a tube (preferably bad tube) in a socket before you solder.

[kleinm]

Thanks for the tip. I didn't realize that was the case at first, until I saw an older post of yours mentioning the exact thing. From that point on, soldering the sockets was much easier.

Any other ideas, anyone?

[drz400]

As it trails off, it will sometimes do this noise.

Yesterday, I was showing the amp to some friends, and the output dropped to a whisper, and was replaced with loud static. Same on both channels. The guitar signal came through, but it was extremely quiet, especially compared to the white noise background.

Well, today I was probing around, and chopsticks didn't reveal anything. I decided to check my voltages, and as soon as I touched my positive probe to B+1, the static went away. Guitar signal back. I checked and reflowed the joints, and everything seemed okay.

A few minutes later, nothing but static. I touched B+3 this time, and it fixed it again.

As I was playing later, the odd intermittent noise came back.

I've tried swapping tubes, checked all grounds...and I can't seem to get to the root of it. Nothing consistently fixes it. Since both problems are intermittent, it makes it very hard to figure out what's going on....

Does anyone have any advice?

Thanks!
- mk

Sounds like parasitic oscillation, maybe some wire layout issue?

[heisthl]

Check the solder joints on the PI cathode(s) wire. I just encounterd the same symptoms on a new build, anything that put signal in the PI like the static caused by a meter probe touching any point would make the amp work. Pushing down on the board near the PI would correct it as well. It was the wire connection at the first tail resistor.

[Funkalicousgroove]

out of curiousity, what kind of board material/wire did you use?

[kleinm]

out of curiousity, what kind of board material/wire did you use?

1/8" G10 Garolite board, Teflon-coated 20awg solid strand and 18awg stranded. Standard stuff from the Brown Note kit.

[kleinm]

Sounds like parasitic oscillation, maybe some wire layout issue?

Interesting.... If it helps, here's a picture of my build.

Thanks for the input. I appreciate it.

[kleinm]

Check the solder joints on the PI cathode(s) wire. I just encounterd the same symptoms on a new build, anything that put signal in the PI like the static caused by a meter probe touching any point would make the amp work. Pushing down on the board near the PI would correct it as well. It was the wire connection at the first tail resistor.

Great. I'll start there. I really appreciate it. I hope to get busy tomorrow....

[kleinm]

Update - today I rebuilt the power supply filter board, reflowed all the tube pins, cleaned up one of my mods, and reflowed the eyelets on the main board.

Result - the sound isn't dropping out anymore, but I'm still getting that odd raygun noise. I've noticed that it only happens on certain notes. Specifically, on F# and G on the high E string, on B, C, F#, G on the B string, and B and C on the G string.

Weird, huh? Should I cut my losses and take it to my tech? I just don't even know where to begin. Its not making any sense....

[mat]

Hi kleinm,

Sad to hear of the problem. I'm the last person to show You where the problem lies but I had too one mystic problem with my build and it appeared to be loose solder joint on one of the pots. Take a magnifying glass and inspect every solder joint on the pots while pulling the wires gently.

Hope You can sort it out with the help from the forum..