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Favorite MiG50 mods and tweaks..

10/10/2005 2:31 PM
Favorite MiG50 mods and tweaks..
good buddy of mine (and guitar #2 in the band) had been shopping for an amp of his own. He found a clean MiG50 for $200 today which I thought was a steal.. So by this time he should own it.  
I am pretty familiar with the circuit (tweaked up 5F6-A/JTM45) and am familiar with the oxymoron of "russian build quality". What would you folks do who run these amps? I am planning on putting in new EL34 outputs, one of my own OT's, biasing it up, cleaning the pots and seeing where we're at.  
Are there any really nasty parts of this thing? Cheap switches, bad pots, evil bias circuit, etc that we'd want to replace sooner than later?  
10/11/2005 5:13 AM

Two things I ran into with mine... first, the input jacks are really cheesy. Mine would lose volume intermittently on stage, and a little "percussive maintenance" would usually fix it. Opened up, I found that the chrome plating had flaked off the input jack and would short the signal to ground. Second, the pots are extremely cheap. If you wanted to make it bulletproof, I'd replace the pots with chassis-mount pots and flying leads. The tube sockets on mine seem pretty decent. The resistors are sized as small as possible and still handle normal operating conditions, so if a tube fails, chances are it'll take out some nearby components.  
I haven't fired mine up in years, but I remember it being a pretty nice-sounding head. I should resurrect it.  
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10/11/2005 5:25 AM
By the way...
If you would, document what you did to your buddy's Mig 50. I'd love to know how it sounds when you get done, and if you come up with any cool ideas I can try on mine. I'm thinking about stuffing mine in a single 12" combo cab for convenience. My best-sounding rig EVER was a BF Bassman head and a single 12" EV-loaded cab. I'm thinking the Mig-50 might get me 80% there.  
10/11/2005 9:50 PM
SpeedRacer Re: pre-lim report..
my buddy brought it over tonight. Store owner said it needed new outputs. My buddy said it was making no noise but everything lit up. I figured B+ issue. Amps should always make some noise if they have plate voltage. Sure enough the HT fuse holder was f'ed up and in 60 seconds we had the thing fired up and rocking. :)  
The pots are CRAP and 3 of them are cracked already..well, I shouldn't say "already" bc if the serial # is real, this amp was #487 in the run. This thing is relatively old. Metal input jacks but plastic on/off and standby switches. tubes look maybe original (still labeled "USSR" on them!) B+ is 580! ouch. I'm going to replace all the pots but it looks like a potentially ugly job. Take out the bracket, unsolder all of the old pots, see if hte new ones fit etc. Definitely going to need some beers for this. ;)  
all in all a great little amp for $250.  
if we do any cool mods I will post on them.  
thanks! - SR
10/11/2005 10:09 PM
Keep us posted.  
I've often contemplated picking up one of these and doing as you are about to.  
10/12/2005 8:03 AM
Wild Bill

Speed, I've done a couple of Sovteks. I was very happy with one particular MIG 50 that was picked up cheap by a local blues player.  
I threw the pcb, jacks and pots away and wired it point-to-point like a 1987. Then I sqeezed in a Hammond 5v/3A xfmr to light up a 5U4. This of course helped the high B+ a fair bit and gave some sag. Tucked a screen choke inside along one "wall".  
Other than that, I just put in my 47 ohm cathode resistors trick and did some cosmetics to remove the Sovtek logos and make it "pretty". And of course, an nfb switch on the back.  
It's a great rockin' blues amp and the guy who owns it refuses to consider ever parting with it!  
Just FYI  
---Wild Bill
10/12/2005 11:20 AM

Nice mods! What'd you do about the filter caps? (all the ones on the PCB I mean) I'll at least be replacing the cheesy switches, putting in new output tubes and of course the pots for now.  
Been thinking about using a couple of zeners to get the B+ back to earth so that he could use EL34 or 6L6 in the amp. Not sure how recent production EL34's would do with nearly 600V on them.. esp if I want to run some real current through them..  
Steve Albini is apparently a big fan of the MiG50 btw.
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