Sovtek Mig 100-U Schematic Request

[bob p]

I'm looking for a schematic for the Sovtek Mig 100-U.

I understand that there are 3 variants of the 100 watt Sovtek Migs, including the Mig 100, Mig 100-H and Mig 100-U, and all 3 are supposed to be different.

I've attached links the only schems I've been able to find so far, one of which appears to be labelled as the Mig 100, and one as the Mig 100-H.


Mig 100: http://music-electronics-forum.com/a...ek-mig-100.jpg

Mig 100-H: http://music-electronics-forum.com/a...ek_mig100h.pdf

Mig 100-U: ???

By any chance does someone have a copy of the Mig 100-U schematic?

TIA

[The Dude]

I've never seen a schematic for the "U", but have fixed them. If I recall, the output section is the same. There are slight preamp differences, but nothing you can't usually figure out. What's wrong with the amp?

[bob p]

I don't have a problem with an amp, I'm just looking for a schematic.

There's an amp that's being offered locally and I'm just trying to determine exactly what it is. I understand that there are 3 variants out there, and based upon internet lore, they're all different. Unfortunately everyone claims they're different but nobody can actually state what the differences are, so I'm looking for a schem to try to sort things out without resorting to tracing a circuit.

thanks for asking.

[Justin Thomas]

Hey Bob,

No schematic available, but I had one to retube & maintenance a few years back. Basically it's a JCM-800, which you probably already know. I can't analyze the circuit to compare, but I'll say it was reasonably well-built, and would stand up to a few component changes. It was actually a pretty solid PCB, with turret-like posts for flying leads from trannies, tube sockets, etc. I may be able to find the pics of the innards that I took.

I had a '78 Marshall JMP 100Watter (basically a very early JCM-800) in at same time, and I'll just say the Sovtek was an unrefined equivalent of the Marshall. I'da taken the Sovtek if offered a choice to pick one. I put a new set of Sovtek 5881WXTs (same as what it came with) and had to replace one tiny cap that had blown (I think in the Presence circuit?) and the owner said it was a radically different amp - back to the glory it had when new. Great punk amps. If the price is right I'd pick it up, scematic or no.

Justin

[vintagekiki]

http://music-electronics-forum.com/t40194/#post394505
Here is a schematic that came with a Mig 100 U

http://music-electronics-forum.com/t40194/

http://forum.metropoulos.net/viewtopic.php?t=38745

http://www.ehx.com/forums/viewthread/3949/

[The Dude]

I'll add, in case you're not familiar with the Mig amps, most of the problems I find with them is because of crappy pots. I've put new pots in many of them. I'll usually use CTS pots and just run wires to the board.

[Zozobra]

I don't have an explicit schem of the 100U but the one posted by vintagekiki might be it. I have two schems for the plain 100, which are very similar 3 stage + CF topologies. I've attached what I have.

[nsubulysses]

Mig 100 is regular gain. Mig 100H is higher gain variant. There is also a Mig 100B which is a bass amp version. The Mig 100U says "all tube lead amplifier" on the front panel and seems to be the rarest of the bunch. I think I've only had 1 ever. I don't remember how it was different in the lead variant compared to Mig100 and Mig100H but I remember it having a lot of gain anyway. Maybe the voicing is slightly brighter for lead playing but that's just a guess.

As an aside there is also a local company that is making their version of the Sovtek head because I guess they are getting pretty desirable these days.

[bob p]

Thanks everyone.

Looking at the 3 schems, it seems that Kiki's schematic (the one that says "Revision F," dated 1 Feb 95) could be the missing link:

Mig 100 Revision F:


If "Revision F" is indeed the 100-U circuit, then it is remarkably similar to the 100-H (Revision G) schematic; the 100-U (Revision F) uses CF drive for the tonestack while the 100-H (Revision G) uses plate drive. Otherwise the topology is the same with only a few subtle component value changes. Looking at the schematic, I don't see any differences between the amps that couldn't be revised with a few minutes of soldering. If that's the case, then there really isn't any difference in the model numbers that's worth paying attention to if you're shopping for one of these amps.

[The Dude]

...... and kudos to vintagekiki for helping everyone with the seemingly endless library of schematics!

[bob p]

I'll add, in case you're not familiar with the Mig amps, most of the problems I find with them is because of crappy pots...

Yes, I seem to remember reading that, though I've never had a Mig on the bench. As I recall the discussions from back in the 90s, these were definitely budget grade amps that used tried and true circuits but were designed to a price point. If things like pots haven't already been upgraded, after 20+ years it's definitely time for that to happen.

As an aside there is also a local company that is making their version of the Sovtek head because I guess they are getting pretty desirable these days.

The used gear market is a funny place. Anything that isn't current production seems to earn a markup for being "vintage" once it gets old enough, without regard for how desirable it was originally. Now that the 1990s Sovteks are 20+ years old it sounds like some people are marketing them as aspirational "vintage gear" instead of admitting that they are still nothing more than budget price point amps whose only virtue is that they're now old enough to need recapping. EH is now exploiting that vintage trend by marketing "vintage reissues" of the old Sovtek Mig 50 under the EH brand name.

If anything that's 20 years old qualifies as desirable vintage gear, then does that mean that we're all going to have to pay exorbitant prices to buy a Bugera, Blackheart or Krank amp if we're still around in 2037? IMO these are the 21st Century equivalent of a what Sovtek used to be -- an inexpensive "offshore" production amp.

From my point of view the 1990s Sovteks will always be inexpensive / cheaply made amps, but now that they're 20+ years old and "vintage", they're old enough to need overhauling. Maybe I'm wrong to think they should still be inexpensive -- but I think they should be even less than inexpensive because they're now at the age that they're going to need preventive maintenance if they haven't already undergone failures. But I'm not looking at them as a vintage gear collector, I look at them in terms of the work that needs to be done to keep them in shape. In that respect, they might be more of a liability until they're fixed, and they're definitely not an aspirational purchase.

I've heard that they've appreciated in price -- which seems counterintuitive to me. What's the market like on these things? I have to admit that I can't see paying a premium for an old one, especially given that EH is cranking out new Migs at a MSRP of $575. Maybe the smart buy is to wait for people to start flipping out of the new production Migs or just get one of the other offshore clones and build that up. Or keep waiting to find a cheap DOA.

[vintagekiki]

https://irationaudio.com/2015/03/26/sovtek-mig-100-u/
Sovtek MIG 100-U

[nosaj]

https://irationaudio.com/2015/03/26/sovtek-mig-100-u/
Sovtek MIG 100-U

Hmmm I wonder whose site that is?

nosaj

[vintagekiki]

Hmmm I wonder whose site that is?

nosaj

https://irationaudio.com/

[Leo_Gnardo]

I've heard that they've appreciated in price -- which seems counterintuitive to me. What's the market like on these things? I have to admit that I can't see paying a premium for an old one, especially given that EH is cranking out new Migs at a MSRP of $575. Maybe the smart buy is to wait for people to start flipping out of the new production Migs or just get one of the other offshore clones and build that up. Or keep waiting to find a cheap DOA.

Sovtek had the price advantage of being built in Russia during a period late 80's to mid 90's when labor and material could be had at rock bottom rates. I've worked on a number of them and they're surprisingly well built. The chassis steel seems to have been meant for tank construction, cold rolled and nearly impossible to drill. Never seen a Sovtek transformer go bad. Many of the parts were mil surplus. Weak points were input jacks, easily enough replaced. Pilot lamp assembly, same. And early ones had awful pots with skinny white plastic shafts. You see any of those, yes just replace 'em all and be done with it.

Price "appreciation" in recent times? Considering how cheap they were when new, Sovtek was a sleeper brand up 'til a couple years ago. People didn't generally respect them in spite of being fairly competent amps similar to Marshall Lead heads of the late 70's. Now the prices have picked up a little. No more $100-250 deals. You can see what they're offered for on Reverb & Ebay, still not awfully expensive, except those offers made by those with pie in the sky ideas. I wasn't aware new Migs were available. If they're as good as the old ones, $575 is a terrific deal. If they're cheapo made in China maybe not so much. New Sensor has expanded their universe from USSR/Russia only to China now as well, and if anybody can hammer out a cheap deal, give the prize to Mike Matthews.

I'd hold out for a nice 50W Midget, one of my customers had a couple of them and they seemed plenty loud enough for just about anything. Pair of wafer base 5881's, you get a clean 48 watts, enough to steam clean your ears.