Sovtek Mig 50 Bias

[plexi50]

I picked up a near mint one owner Mig 50 this morning from an old guy (like us) for $50.00
I place adds to buy amps on CL and really didnt expect him to show up at this price

He did. Another WOW! day. Anyway this amp is running roughly the same plate & bias as a Mig 50 i used to own several years ago
525VDC @ -55mv grid / I know i need to get a good bias tester

I have read online that they usually are setup to run 480 PV @ -36 to -41 ma

What is your Mig 50 bias and PV findings? Sounds great. Has that 800 bottom end and mid scoop
The PC Board is much different than the one i used to have. It is a thicker fiberglass board and brown in color instead of red
The caps are dated 4th week of 1993. Looks like the owner has the plastic jacks replaced with switchcraft and some pots

http://s356.photobucket.com/albums/oo5/plexijtm45/?action=view&current=c89e5c05.pbw

[TubeGeek]

Good deal!

With your plate voltage of 525VDC...

6L6 max plate dissipation is 30W

common range is 70% of max plate dissipation = 21W

plate vdc 525vdc * 0.055A (55ma) = 28.9W

I'd say your tubes are biased hot (96% of mpd) and if this were on my bench, I'd experiment a little bit with the bias and see the effect on tone you hear and go from there.  As long as the 6L6's aren't red plating, you're good.  It's all preference.

With a plate voltage of 480 vdc...

480 * 0.036A (36mA) = 17.28W  (closer to the 70% of mpd range or safer zone)

480 * 0.041A (41mA) = 19.68W (even closer to 70% of mpd)

[plexi50]

Thanks TubeGeek! I backed off all the way on the bias trimmer but it only got me to 518 PV so i think i need to change the bias resistor or put a larger trimmer pot on the board

I would rather have it running at 480 PV and lower the beast in it a bit

I still dont believe the guy showed up with this. He said he bought a new Egnater amp and was going to throw it away in the garbage

This is why i run adds from time to time. You never know whats going to happen. The tubes are worth more than $50.00
The condition of the amp and cab itself is amazing for it's age. Surreal

[TubeGeek]

Adjusting the bias pot and monitoring the change of plate voltage is not recommended.  The plate voltage will change with any bias adjustment but we aren't using the bias to control plates, you want to monitor the current going through the tube and go off of that.

Either build one of those bias tools or install 1ohm resistors from the cathode to ground.  Then meter that and see how the current changes when you swing the pot.  If you cannot get the bias current in the range you want, then its time to change a bias circuit resistor to get you in the right range.

[EL34]

You don't bias amps by some sort of made up voltage figure

You read the current flowing through the power tube.

Put one ohm resistors on the cathodes or get one of my bias tools

[plexi50]

You don't bias amps by some sort of made up voltage figure

You read the current flowing through the power tube.

Put one ohm resistors on the cathodes or get one of my bias tools

Thanks for the push Doug. I will be ordering a bias kit from you in the next few days. I wasnt tring to bias the amp at that point. I was just seeing how much travel i had in the 10K bias pot and what the plate voltage went to. A momentary look

[EL34]

Those old migs were cool
I worked on several of them in the 90's

The board layouts were a mirror image of most other amps

Other than that, I don't remember a whole bunch about them
 

[plexi50]

They have that deep throaty sound (Not Linda Lovelace)

[jjackson7]

I used to have a MIG 100. Great amp . I remember the plate voltage was around 550. I used the transformer shunt method  when I had it but I can tell you from experience that amp can take more abuse than most and still sound great. I'm really not sure why those aren't held in higher esteem. Great steal on that amp by the way. Missed out on a CL deal for a MIG100 half stack for 350 last year. Still pissed!

[plexi50]

I used to have a MIG 100. Great amp . I remember the plate voltage was around 550. I used the transformer shunt method  when I had it but I can tell you from experience that amp can take more abuse than most and still sound great. I'm really not sure why those aren't held in higher esteem. Great steal on that amp by the way. Missed out on a CL deal for a MIG100 half stack for 350 last year. Still pissed!

I still dont believe he showed up for $50.00. Man thats like hitting the lottery in a way

[alerich]

CL is a wasteland here in Atlanta. Nothing but idiots and scammers and kids on their parent's computers who like to jack around with people. Not really worth the time and trouble. That was a good score. I'll bet it can be made into a nice amp. The few MIGs that I have played were all sorta mushy once tey became overdriven but sounded like they had mod potential.

[plexi50]

I got another response to my add's last night. A 1948 Fender Pro that was going in the garbage if i was not interested in it. Now i know a dummy email when in see one. I offered them $100.00+ for it but i dont expect a response   If it is i will email you from Morton Plant Hospital after i have an amp attack

[SoundmasterG]

Was your 50 watt Sovtek a MIG 50, or a MIG 50H Midget? I had one of those Midgets that I bought brand new...it was a good amp and never let me down. It sounded like they were trying to do a JCM800 thing with it, but used 6L6's instead. I thought about sticking EL34's in there and trying it, but I ende dup selling it and building myself a JCM800 clone.

I was also given a MIG 100 U, which was a really early one. It was non-functional, so I fixed it, but it sounded loud and thin. So I kept the chassis and power transformer, gutted the rest, and built my own amp in it. A clone of a Vox AC100 with my own second channel added. I'm not entirely done with it, but it sounds fantastic. The iron on those Sovteks is pretty good. I still have the OT and choke from the MIG 100 U but haven't figured out what to do with them yet.....

Greg

[plexi50]

It is a Mig 50. There was a year where they had some bad transformers. I cant remember the year. My serial starts with 001. I tryed El34's in one a few years back and liked them. I am more Fender oriented these days and have come to appreciate the blues &  jazz tone i get from 6V6 & 6L6GC. I love my Peavey Classic 30 and 50 amps. I just bought a 1993 Classic 50 4x12 in mint condition friday night
The Migs do have a different tone that i think can only be attributed to the output transformer and just maybe thoses russian caps and resistors may have some Stalin in them. I have not owned the Red Bear yet. I hear they are good amps

[Colas LeGrippa]

...some Stalin in them ? D' you mean it's a killer amp ?