Sovtek MIG 50H input jack upgrade

[ModdersAnon]

Hello all,

I've recently ran into a problem with the input Jacks on my Sovtek tube midget(master volume)
The plastic nut on the inputs are a constant source of woe and the only issue I've ever had with this amp....coming loose and spinning, pulling wires from solder grrrrrrrrrrrr

What are some good replacements? preferably metal, although with those soundguruman said I would need some insulation.

also, I found that the pots are Mouser and are attached to the faceplate and not to the board

[ATTACH=CONFIG]16687[/ATTACH]
I have been using Precision Electronics Canada Pots in MIGS.
These pots have a great super-even taper (reverse log / audio) that maintains adjustment all the way from top to bottom, and an extended rotational range of 130 degrees. These things blow away consumer grade controls, it's like night and day.
[ATTACH=CONFIG]16688[/ATTACH]
As you can see, the circuit board and hardware will need a bit of tweaking, to shim the pots to the correct height.
[ATTACH=CONFIG]16689[/ATTACH]
and the faceplate needs to be drilled out a few thousandths of an inch, but not a whole lot...
Then, you will need to use 1/4 shaft knobs, I prefer the Fender type, because you cannot use knobs with brass set screws. The shaft of the pot is stainless steel, and you must use knobs with steel set screws, not brass.
These type of pots can be had for about $10 each, but some vendors have been selling them for quite a bit more.

The jacks should be replaced with CLIFF (Marshall type) OR if you want to use steel jacks, you are going to need insulators, to prevent the jack from grounding to the faceplate. (this produces a ground loop- BUZZ)

But the end result being, that there is actually hardware holding the pots solidly to the chassis, and the shaft of the pot is no longer (flopping about) at the mercy of the environment.

There are also BOURNS pots, conductive plastic, with 1/4" steel shafts, that will solder right onto the board, However, you will probably find that nobody stocks the values, and they have to be custom ordered and configured. The Bourns pots also have hardware (threaded bushings) to attach the pot solidly to the chassis. The Bourns pot does not have the 130 degree rotation, and does not have the special taper, to allow smooth adjustment all the way from top to bottom.

Actually, people would be surprised to find that the MIG (other than the controls) is a pretty solid guitar amp. It's built really strong, and has nice beefy transformers. It also invites rather easy modifications. I kinda like it myself....

[ModdersAnon]

there was this ring that was being grounded straight to the chassis. would that eliminate the need for insulators for metal jacks?

[soundguruman]

I don't understand what "this ring" is. You need to give much more details.
The idea is to eliminate multiple ground points, and just have ONE preamp ground.

[ModdersAnon]

Here you go. detail of the switch and ground along with a snip of the schematic showing the input wiring.

Is it my lack of electrical wiring knowledge, or has something been altered not following the schematic. Did the tech who repaired it last time take some liberty with the wiring?

edit: almost forgot to add, there was one wire barely hanging that was soldered to the juncture of the purple and yellow wire
and another wire that was completely loose and I must determine where it is supposed to be connected

Thanks

[Enzo]

That hoop grounds the circuit at teh jack. That jack is insulated, but they wanted a ground at that point, so they added the hoop.

I highly recommend you don;t change the grounding schemes until you are sure what you are doing.

Looking at your photo, top edge of the jack, are three solder tabs, and the center one appears to have a tiny remnant of a yellow insulated wire. Is that correct or just an illusion? And unless I am confused, highly possible that, I would kinda expect to see a wire from the lower right terminal to that ground point as well.

[ModdersAnon]

Yes you are correct about the bit of yellow wire.

There is some bare solder on that lower right terminal, but it is nice round bead and doesn't look like any wire was ever connected.
BTW this jack is different than the Low input leading me to believe it has been replaced when serviced several years back. perhaps a used jack was substituted for the OEM during service