Sovtek Mig 50 making static noise

[Ghostplanet]

I have a sovtek mig50h. It is making a static noise. I have reaplaced all the tubes and power filter caps. The amp does pass the guitars signal clearly but there is also static. Any ideas? Thanks.

[tubenit]

IF you know how to work on amps safely,  you can "chopstick" solder joints with a non-conductive stick like a chopstick or wood dowel.  As you gently tap on different areas, listen to see if it creates static tapping on that area?  IF so, then look closely at solder joints and connections. You may have a bad solder joint or IF this is a PCB board, have a bad trace or solder joint.

IF an amp is starting to redplate on the power tubes, that can create static,oscillations or distortion.

With respect, Tubenit

[Ghostplanet]

Thanks for the info, I will check the solder joints. I do know enough about working on amps to be safe.

[John]

Does it make the static all the time, or just on certain notes?

[Ghostplanet]

All the time.

[John]

Hmm. Check the joints on your plate resistors & power resistors first. If it's easy to do, replace the plate resistors with metal films. Also, when it's making static, grab the preamp tubes (they take a while to get good n hot) and see if maybe they're the problem. Well, this is what I'd try first if it was me, anyway. :)

[Ritchie200]

+1 and do the easy stuff first.  Check and clean all tube sockets and re-tension if needed.  Check input jacks for good grounds.

Good luck!
Jim

[2deaf]

Sovtek MIG 50H - - Non-invasive diagnostics

I.  Turn "Master" off - - Still has static
     A.  Not V1 or V2 and associated circuitry.
     B.  Pull V3 - - Still has static
          1.  Not V1, V2, or V3 and associated circuitry up to V3 plates.
     C.  Pull V3 - - Static gone
          1.  Problem with PI (V3)

II.  Turn "Master" off - - Static gone
     A.  Not PI (V3) or 5881's and associated circuitry.
     B.  Turn "Master" up, "Volume" off.
          1.  Static returns - - Problem with V2 and/or associated circuitry.
          2.  Static still gone - - Problem with V1 and/or associated circuitry.

[Ghostplanet]

Thank you all so much for the good tips. I will try them and get back to you all.

[terminalgs]

Does it have the original pots?  Those pots are junk.  On my MIG50 the original pots started failing,,  making noise, not passing signal etc... I replaced them all (PITA on a mig50!!)

[Ghostplanet]

I did the test recommended by 2 deaf. With either the Master or Vol all the way down the static goes away. By that logic is could be V1. Also when I turn the Treble pot all the way up the static gets higher pitched and worse. Dont know if that helps.

[Ghostplanet]

I have the smalls pots that I use for building stompboxes, can I use those in my amp or do I need more heavy duty ones?

[SILVERGUN]

I have the smalls pots that I use for building stompboxes, can I use those in my amp or do I need more heavy duty ones?

1/4 watt pots are ok but usually flimsier than 1/2 watt and higher.
We like to build amps with "heavy duty" parts so that we don't have to do it again in the foreseeable future. If you're not much of a pot spinner then your mileage will vary. There's also the case of the shaft diameter. The pots that are in there have very small shafts and will probably have to get enlarged. The square, plastic, multi-colored pots that were in mine had very tiny shafts.

If you've completed all of 2deaf's troubleshooting and it has led you to V1, you should just try a different tube. A microphinic tube in that location gets amplified at every gain stage thereafter.

Don't be afraid to do the pots like this:

[Ghostplanet]

I will try a new tube in V1. If that doesn't fix the prob I will try the pots. I will try the ones I have on hand to trouble shoot. If that fixes the static I will order 1/2 watt pots. Again thank you all for the help.

[alerich]

Does it have the original pots?  Those pots are junk.  On my MIG50 the original pots started failing,,  making noise, not passing signal etc... I replaced them all (PITA on a mig50!!)

The pots on my Mig 60 are not board mounted so they were a breeze to replace but recapping the power supply? Pffft. Forget about sourcing a replacement for those Russian military surplus cap cans. I ended up retiring them in place and installing axial replacements inside the amp. Luckily there is sufficient space inside a Mig60 for this. At least I no longer have one hot cap can with 350 VDC on it.

I am surprised that their amp models differ so greatly in topology. The Mig60 is pretty easy to work on. Lots of socket mounted components and flying leads to all sockets and pots. The Mig 50 and Mig50 Midget? Fuggedaboutit. Not a fun time.

[Ghostplanet]

I think I may have it. This morning I GENTLY wiggled the preamp tubes, and V1 made a ton of noise. I replaced it, and the noise got better, but there was still a little noise. I inched it out a tiny bit, just enough so it was still making contact, and the noise was gone. It may be a simple as a dirty tube socket. I will pick up some contact cleaner and try that.