Sovtek Mig100h Clone

[NFXP]

I recently bought someones attempt to clone a Sovtek MIG 100h clone. looks like he spent a bit on money on this with all new parts. I bought it cheap enough to sell off the parts if i needed.







I think i have already found the fatal blow, the main pt is 1250V! from what i looked up it should be 360V. I think maybe the dude thought 360v per tube. So 360 x 4 = 1440V. So i guess my question is is there any hope. or any other amps buildable from this PT

[Chuck H]

Can you take a close up pic of the label on the PT and post it?

[NFXP]

And the ot since i had the cam out. but that looks alright.

[J M Fahey]

Sorry to sound like a party buster, but looking at the *huge* (and that's the understatement of the year) mistake done when using that transformer, plus the "science fair project" technology used in the construction, makes me doubt *a lot* about everything else there.
Just the use of separate chassis alone is going to be a grounding nightmare.
Consider it a collection of parts, get a usable power transformer and a regular chassis and you can build a working Mig 100 or something else.
I would not even plug that one, not even for testing, I have a hunch it may be dangerous in more than a way.
May be wrong, of course, but better safe than sorry.
Just take it apart and turn it back into a kit, then you decide.
EBay the transformer, maybe somebody is just trying to build a 1750V PSU for his amateur 1250MHz band transmitter or similar exotic (for us) application.
Good luck.
PS: pity the clearly painstaking work and long hours spent in building this.

[NFXP]

Sorry to sound like a party buster, but looking at the *huge* (and that's the understatement of the year) mistake done when using that transformer, plus the "science fair project" technology used in the construction, makes me doubt *a lot* about everything else there.
Just the use of separate chassis alone is going to be a grounding nightmare.
Consider it a collection of parts, get a usable power transformer and a regular chassis and you can build a working Mig 100 or something else.
I would not even plug that one, not even for testing, I have a hunch it may be dangerous in more than a way.
May be wrong, of course, but better safe than sorry.
Just take it apart and turn it back into a kit, then you decide.
EBay the transformer, maybe somebody is just trying to build a 1750V PSU for his amateur 1250MHz band transmitter or similar exotic (for us) application.
Good luck.
PS: pity the clearly painstaking work and long hours spent in building this.

First off i would never plug in someone elses handy work without going over it completely as if i were building it. The story goes buddy hooked up the first heater transformer for v1 (sovteks have some sort of buffer on V1 heater) and blew a cap and got real scared and didn't test any other circuits (which is a good thing with that PT)
As for the chassis issue he used a machined grounding block which all looks really well done. He spared no expense using stainless machine screws instead of rivets, he gave me the boxes for the tubes and there were fender packaging for pots in there too.

Anyone know a good source for a 360vct 300ma PT
Or anyone want to buy said 1250v PT.

[soundmasterg]

I have an early Mig 100 U that I built into a Vox AC100 clone. I kept the Sovtek power transformer but used Heyboer iron for the OT and choke. So if you were interested, I have an actual Sovtek Mig 100 OT and choke, and the actual Sovtek Mig 100 board and parts that I would sell cheap. Say $60 + shipping for all of it?

If you're interested, send me a pm.

Greg

[J M Fahey]

First off i would never plug in someone elses handy work without going over it completely as if i were building it.

Never doubted it.
As of the power transformer specs, 360VAC is somewhat hairy for any modern 6L6/5881 (and for most of the old ones).
I would never go above 320VAC. 315VAC would be even safer.
And 300 mA sounds too tight, I would feel comfortable with at least 400mA, preferably 500mA.
Good luck.

[Chuck H]

FWIW the OP indicated that he wanted a 360vct... So that would be a 180-0-180??? Wayyy too low actually.

The OP could also use that strappin PT with something like an 811A tube and build a 50W Champ clone

[J M Fahey]

In general that would be true but please check the Mig100 schematic.
It uses an end to end bridge rectified circuit, the center tap simply provides a stiffer center tap (duh) for the series connected filter capacitors.
The total voltage is still 1.4142 x end to end voltage.
360VAC would supply almost 510V DC.

[Chuck H]

Ahhh, right. Sorry, never opened the schem to see that it's a bridge and not a full wave rectifier.

[NFXP]

I have an early Mig 100 U that I built into a Vox AC100 clone. I kept the Sovtek power transformer but used Heyboer iron for the OT and choke. So if you were interested, I have an actual Sovtek Mig 100 OT and choke, and the actual Sovtek Mig 100 board and parts that I would sell cheap. Say $60 + shipping for all of it?
Greg

Whats the mig PT specs your using, i could only found some loose details on the net.

Never doubted it.
As of the power transformer specs, 360VAC is somewhat hairy for any modern 6L6/5881 (and for most of the old ones).
I would never go above 320VAC. 315VAC would be even safer.
And 300 mA sounds too tight, I would feel comfortable with at least 400mA, preferably 500mA.
Good luck.

If i can find a suitable PT i will try to salvage this project, i dont know the actual specs so if no one comes through with first hand knowledge ill will have to take sugestions.

[Chuck H]

If i can find a suitable PT i will try to salvage this project, i dont know the actual specs so if no one comes through with first hand knowledge ill will have to take sugestions.

I think you'll still need to build on a proper chassis. Regardless of the care taken in the existing build ground plane or expense of components the components and leads aren't shielded and honestly it looks like a layout nightmare. I doubt it would be stabil under OD conditions. JM2C.

[NFXP]

The deal is if i can get it to "work" in any capacity buddy will buy it back from me + pay me my work. So im going to try as a long shot to get it working and if i do then buddy will get his project back and he can carry on with it, make a chassis or whatever he wants. if it becomes too much work or too expensive then its going for parts. Sorry if ive lead you guys on but im more of a 2 to 5 watt guy. i cant stand 100 watt amps, i own one but i never use it. Either way i looked at this a project to part out or as a challenge in my free time. win win.

[soundmasterg]

Whats the mig PT specs your using, i could only found some loose details on the net.



If i can find a suitable PT i will try to salvage this project, i dont know the actual specs so if no one comes through with first hand knowledge ill will have to take sugestions.

I have no idea of what the actual specs of the PT are. In operation in the amp, the B+ at idle was right around what a Vox AC100 is, which is about 470v. With no load, it was really close to 500, might have been a bit higher...I forgot. All the Sovtek amps had high voltages in them, with the MIG60 pushing 600v using Sovtek EL34G's! Insanity!!

Anyway, so if you backtrack, you could figure it is probably about a 350-0-350 PT. The MIG 100U was very similar to the MIG100H, but was an early version. It used regulated DC filaments for the first preamp tube, and had a tap that was around 13v unloaded for that. That tap would not run any more than 1 tube's filaments, so it isn't rated for much current on that tap. The PT does just fine with a quad of EL34's and the 1.4mA or so that the filaments are requiring for my preamp and the Vox preamp I stuck in it so the PT is pretty stout. It doesn't get hot at all in operation.

I guess since you are into low wattage amps then you won't be into the OT, choke, or circuit board with all parts for this one, but didn't hurt to ask. If anyone else is interested, you know where to find me.

Greg

[Chuck H]

Anyway, so if you backtrack, you could figure it is probably about a 350-0-350 PT.

I did the same thing. Mr. Fahey was good enough to point it out. It's a bridge rectifier, not a full wave. So a 350-0-350 PT would have no use for the "0" and the 700V starting point is going to be too high.