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Re: Cheap Tube Amp Alert $199.99

8/24/2000 5:42 PM
Re: Cheap Tube Amp Alert $199.99
A few years ago, I was able to get a copy of the schematics for two Sovtek amps, the "Mig 50", and the "Tube Midget". The midget's title block does indeed say it's model Mig 50H. It has the first two preamp stages cascaded (like a JCM 800), and a simple tab transistor regulated DC supply for the first 12AX7 heater. I don't have the schem for a Mig 60 or Mig 100, so can't compare similarities.  
8/24/2000 6:40 PM

A mig 60 is basically a JCM800/70's MV marshall, few component changes, but sond is just like the MV mk-II's of the late 70's IMHO... all SOvtek amps are a bitch to mod. you wont find color coding on the wires... all white... and the mig60 I had, was a bunch of small PCB + some handwired parts, and the PCB's were pretyt bad
8/24/2000 7:24 PM
I have some schematics of these heads..The mig 50 is the bassman knockoff..a few things about them..they have chep-O pots..and are not made as well as the mig 60..wichis like posted a MV knockoff amp.. The 100 ..the one that has the master is like a 2203 kinda amp.. loud as Hell too.  
The other thing is.. I have a mig50 on the bench right now..and it runs different heaters for the tubes..The other thing is the transformers in the amps.. are able to switch from 110 to 220.. the 110 makes this amp have alot of house voltage runs around 123 volts.. Now who has the mod to tame this beast.. with the voltage dropping ..  
I hope its not the one where you put a 220 pigtail cord on the amp and run it on  
These are harder to mod.. and the resistors are wireded to read .. But the schematics list them as USA values..And the wires are alot the same colors,with numbers in white wrapped on the ends.. So if you get one in and someone cut the ends off all the blue wire.. and says all it needs is the switches wired.. you have to trace all this out to find where they go. The mig 60 has rectified heaters on the preamp..But still for the money.. they can be a great amp.. even for modding or head to build from.The one i'm working on now..someone put in a tube socket,wired wrong and burnt things all over,got most of it done but an input jack and volume pot.. but this thing is running 575v..on the 5881..  
8/24/2000 8:03 PM

The Quick Fix:  
You need to install a voltage bucking transformer in series with the 110v primary. A 12v/3A filament trans is ideal. RShack has them. (You'll have one in a box under the bench.) The idea is to connect the 12vac winding in series but out of phase with the Mig's 110v primary. The net result is 125v mains minus 12v = 113vac impressed on the primary winding of the Mig. Everything back to design normal.  
R.G. has the hookup diagram for this on his GEO. (I know you won't need the diagram, but others might.)  
8/25/2000 1:41 AM
Thanks So much Doc!!  
8/25/2000 6:37 AM
Steve A.

but this thing is running 575v..on the 5881..  
    I had heard that the B+ on the Sovteks is pretty high, more so than the ~10% difference from 110 to 123vac. If you are looking for a more authentic Bassman or Marshall sound you might want to wire in a stud-mounted power zener.  
    My theory on these cheap imported amps is that they try to use the same PT as much as possible throughout the world, which may have a line voltage between 90 or 100vac and 250+vac (does anybody get 277vac from their power outlets?) Like I bet that Pignose uses the same PT for their G40V whether your line voltage is 95vac or 145vac...  
    BTW what sort of voltage do you measure on the filaments? If that is higher than 6.3vac it might give us an idea what the input voltage is really supposed to be...  
Steve Ahola
8/25/2000 9:34 PM
Maybe a couple transformers.. and install a tube rectifier,and the other to fix the heater voltage..  

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