SovTek Mig 50 pot values & taper

[guitarslam]

I want to change out the (cheap) PC-mounted pots on my Mig 50 head.
This is the non-master volume version.

It would be much appreciated if someone here could post the values and respective tapers for the volume, bass, mid, treble and presence pots?

TIA.
Cheers,
Glen H.

[Enzo]

There are so many versions...

You can measure them. Total resistance is total resistance, regardless of taper. Then set the shaft at mid turn and measure from center leg to either end. If it is about the same to each end, it is linear, and if it is way off, then you have a log or audio taper of some sort.

In general:

Volumes - 1 meg log
Presence - 5k lin.
Bass - 1 meg log
Mid - 25k lin.
Treble- 250k lin in some and 500k log in others

[Burchtone]

Guitarslam,

I have one of the first series Mig50 amps. The pot values in mine are:

Vol I =1Meg Audio Taper
Vol II =1Meg Audio Taper
Treble= 250k Audio (Marshalls are typically 250kL here)
Mid=50k Linear Taper (Marshalls are typically 25kL here)
Bass =1Meg Audio Taper
Presence =5k Linear Taper

I hope this helps!
I plan to replace the pots in mine, too. That is if I can figure out why it keeps blowing the 3.15A fuse!!!

[guitarslam]

Thanks Guys!

The info. provided is much appreciated!

Cheers,
Glen H.

[Burchtone]

guitarslam,

If you are not sure which pots to buy as replacements, you can use something similar to Alpha 24mm pots. They barely clear the PCB. I did this to mine and it worked just fine. Anything larger than a 24mm and you may run into trouble.

[guitarslam]

info much appreciated!

I look forward to overhauling this amp.
These early Mig 50s really do have great tone, which rank equally with my 1960's Traynors and Marshalls.

Cheers,
Glen H.

[Burchtone]

It's a great amp. I have replaced the flying leads (where I could) with better quality heavier gauge wire, as well as replaced the pots. I bought this amp new many years ago. It crapped out a few years back and kept popping the mains fuse. I went through the whole rundown of trying to find where the problem was. It turned out the be one leg of the bridge rectifier. I pulled it and replaced it with a Fairchild unit that was about 3x the size, but the same ratings. I bent the leads and soldered it in. It works perfectly now. Apparently, there were quite a few rectifier failures on these amps. Be aware of this if you start having problems.

My amp varies quite a bit from the posted Mission Amps schematic. There are several places where it has some minor value changes. There are a couple other places where there are significant deviations. The power section appears to be very different than drawn, in both values and configuration. I'm guessing Sovtek/New Sensor/Electro Harmonix varied the values and configuration to use whatever they had on hand at the time. Mine is setup very much like a JTM45 with the split cathode of a Lead and it sounds very much like the early Marshalls. I wish I had bought two of these amps when I had the chance.

Good luck on your repair.

[guitarslam]

Thanks Guys! Mig 50 pots replaced = success

I finally got around to replacing the stock pots with better quality ones. Flying leads were used, as the old pots were mounted directly to the board.
I could not be happier with the results

Thanks to all who helped by providing useful information and tips.

cheers,
Glen H.

[Froham]

Guitarslam,

I have one of the first series Mig50 amps. The pot values in mine are:

Vol I =1Meg Audio Taper
Vol II =1Meg Audio Taper
Treble= 250k Audio (Marshalls are typically 250kL here)
Mid=50k Linear Taper (Marshalls are typically 25kL here)
Bass =1Meg Audio Taper
Presence =5k Linear Taper

I hope this helps!
I plan to replace the pots in mine, too. That is if I can figure out why it keeps blowing the 3.15A fuse!!!

What is the advantage in using audio taper pots. Wouldn't linear be more user friendly?

[soundmasterg]

It depends on which position you use the pot as to which taper you want. Because of the way we as humans hear, an audio taper pot will work better for a volume control than a linear taper will. They sound more natural. If you use a linear taper as a volume control, the volume comes up very suddenly and then doesn't get much louder as you rotate it. An audio taper pot will appear to be more gradual.

Greg