Tech help for my Russian death box please

[Iommic Pope]

For all you who know way more about this than I:
I took today, as my back is still not up to going back to work, and thought, "you know what? Kids are at daycare, wife is at work, lets churn out some riffage! "

So I was playing away for about half an hour, with the volume in the off position (its lives there by default, as a Sovtek does not know what for you mean by this "quiet", its still loud with the volume rolled all the way off, crappy pots) and then I thought "hmmm, needs more volume, that does," so i cranked it to 2 and a little on the dial (which is loud enough for my 2x12 and a little room) and I was playing some nice long lazy triads, letting the Black Forest get that crust on the notes, when all of a sudden, its like somebody turned my amp down. I look over and the power light is off, but the switches are still on. Hmmmmm. (No pop sound at all while playing by the way.)
Turn everything off, go to the back of the amp, both fuses still in tact. Hmmmm.

Turn it back on, not throwing fuses still, there's the slight buzzing/humming sound that it usually makes when its connected to power and on standby, but nothing is lighting up: no power light, no tubes. Hmmmm.

I haven't pulled it apart yet, thought I'd check here before i went racing in there.

So, what happened? What do I need to do?
(Recap)
Sovtek Mig-50, into Orange 2x12 (impedance both in the right holes at 16ohms), no power, NO blown fuses.

Baffled.

[Iommic Pope]

UPDATE: After giving it a rest, I went back and it was fine....although to my ear it now sounds a bit more brittle? Could be psychosomatic, but it doesn't feel like the overwhelming flubbiness of the bass is still there. If a filter cap blew, nothing would make noise, right?

I am now truly baffled.

Also, perhaps noteworthy, I took my Supa Puss out of the effects chain this time around, as when i stomped on it, it was like stepping on a low pass filter. I think I need to get a separate power supply for that thing...or to just replace it. It sounds nice but it is starting to become a real pain in the arse.

[AxAxSxS]

Do you have spare tubes? I'd do some swapping with known good and then go from there. If it does suddenly sound better with new ones in there, bias it and rawk on. Also could be it needs a good cleaning? re-tension the sockets?

I don't know what you know about working on amps so I'll leave you with this in case you decide to crack it open http://ampmaker.com/discharging-capacitors-946-0.html

[Iommic Pope]

Hey thanks man. I don't have a spare set of 6l6s lying around to test. Could be the case. Should look into the preamps as well, they are ancient and crap sovteks. The sockets all need replacing. I did one, haven't had time to do the lot. Should probably replace the pots while I'm in there too...it might be time to stop putting all that work off.
All savvy with the discharging as well, cheers. Not a fan of high voltage in my body, just in my amp.

[crohny]

new pre amp tubes possibly. My amp did this when my pre amp tubes were dying. Also the supa puss sounds like it needs it's own power supply or you need to upgrade your power supply to something that allows for high draw pedals which the supa puss is from what I remember. What are you using for a power supply?

[Iommic Pope]

new pre amp tubes possibly. My amp did this when my pre amp tubes were dying. Also the supa puss sounds like it needs it's own power supply or you need to upgrade your power supply to something that allows for high draw pedals which the supa puss is from what I remember. What are you using for a power supply?

Yeah, it will need new preamps soon. Interesting though, that they would cause that.
Yeah I have a one spot sort of dealy that puts out 1100mA. There isn't that much in the chain, (wah, polytune, black forest, supapuss, trinity. in that order) and there isn't that much on at the same time, so I wouldn't have thought draw would be too big a problem. I am going to get another supply for it though, just to be sure, plus its good to have a back up.

[AxAxSxS]

new pre amp tubes possibly. My amp did this when my pre amp tubes were dying. Also the supa puss sounds like it needs it's own power supply or you need to upgrade your power supply to something that allows for high draw pedals which the supa puss is from what I remember. What are you using for a power supply?

Very possible. I had been having intermittent issues with one of my earth heads recently and when I switched around some preamp tubes it did exactly what you described. Power on, transformer hum, fuse fine, no output. I replaced one and it came back to life sounding as good as ever.

It motivated me to finally purchase a real tube tester. should be here tomorrow.

[Iommic Pope]

Yeah dude it's bizarre, do you know which one it turned out to be? Cause that sort of makes me suspicious of the phase inverter.
I did replace v1 when I first got it with a tung sol that was relatively new, known not to be dodgey at least, but it was the only spare I had.
Hmmm, might be time to order some new ones....and do the rest of that work.
Cheers fellas.

[AxAxSxS]

v2 for me.

[Iommic Pope]

It happened again.
To reiterate, from my DR post:
I'm pretty sure its v3, the phase inverter, as it won't light up, and then the power section stays cold as well. Preamps are getting current when switched on (v1 and 2, but funnily enough, no power lamp....crazy russians), so I'm guessing that if v3 is a no show then current won't flow to the power section? Is that right?
I have 3 12ax7s that won't make the magic happen right now, but I'll try it again later and see if it works, cause it did last time.
My gut tells me its not just the tubes but something else...but I was thinking, if I switched to a 12at7 in the pi, it might not overheat as easy with those crazy shit voltages running around?

So, do I go order some new tubes and try an at or should I be looking for something else?

[Iommic Pope]

OK, just went and turned it on again now everything's cold, and everything is back in action.
So, heat issues?

[AxAxSxS]

Weird man, Need a Sovtek Guru to pop on here. What circuit are those based off of?

[Iommic Pope]

Yeah man, very strange.
The Mig 50 is supposed to be like a bassman/plexi kind of circuit.

http://www.blueguitar.org/new/schem/sovtek/mig-50.pdf

Everybody seems to agree that this is one of the better schematics out there...however not all units are built this way. In typical Russian fashion.

I'm gonna put my $$ on heating issues. I was reading that the PI on this can read anywhere up to 360v, which would definitely start to cook ax7s (which I have in there now). I haven't taken a reading yet. When I biased my new tubes last time I was getting 620v+ on them, so I wouldn't be surprised if v3 was in that 360v area. I did crank the volume up to like 9 o'clock, which I haven't done in ages, and after about 20 mins of playing, so it would've already been toasty.
I'm gonna order a couple of 12at7s anyhow, see if any of em survive. Hopefully I can nab a rogue that can withstand those conditions. Looking at the Philips JAN military spec, maybe? Or EHX. I dunno. I may potentially just bulk order a ton of cheapies and treat them as throw aways until I can come up with a better solution. Although I am super reluctant to start putting in extra resistors to bring that motherfucker down. I have no idea what that might lead to as far as the rest of the amp is concerned.

[HeavyXIII]

I've got some JAN 12at7s in my amp, but in v3 and v4 (FX loop and PI respectively). I read they handle voltages more efficiently and provide a better signal from the preamp to the poweramp. They supposedly don't die like 12ax7s in the PI position, but I'm sure you've figured that out already if you're planning on ordering some. The JAN stuff is good tubes, and I was able to find some online at thetubestore or something for about $12 a pop.

Damned amps and their unreliable schematics.

[Iommic Pope]

Yo, cheers for the good word on them, man. Yeah I've been having a stickybeak and I think they might be the go, they're the right price.
I just read somewhere that apparently 12at7s can 550v plate in reality, but just aren't specd that way officially (on datasheets). I know that they do that sort of stuff with power tubes just to be safe, but does anyone know what the real deal with that is?