I just realized I left out an entire section of this repair... I found some old Sovtek MIG knobs in my parts stash from a different MIG I had a while back. I drilled them out and gave this amp a full compliment of original MIG knobs. I filmed that part but forgot about it in editing. Oops. Oh well.
The caps probably weigh more than any other component on the board, so they have the most inertia. If the amp is jostled, they may threaten to break the solder connections on the underside of the board. Those traces are fragile and it's best to do what you can to keep that from happening. Increases long-term reliability. Also, you'll notice I did not de-solder the original leads, but instead clipped them off the old caps and soldered the new caps to those. That kept me from having to disturb the traces on the board also. Too much iron heat and those can just call apart on you.
In russian slang "Sarai" translates to shithole; so the fact that the prefix of the named city is pronounced that way it made that shithole very special!
Aleksey Chernozubkin i loved those amps brother. I sold at least 100 of them. I used to mod them and sell them. They ripped. I wish we could still get them.
Why would someone talking about electronics repair need experience as a musician? Are you good at repairing amps? Maybe you shouldn't be playing guitar, then. Your logic.
I always establish negative bias supply first.. without it, obviously the power tubes will turn on hard and red plate... Been building hi fidelity tube gear since before you were born, so this is voice of experience. I must say though that you have learned the craft of musical instrument amps damn well and find your vids refreshingly competent, with a nice bit of music tossed in for great fun.
I wouldn't doubt it. Sovtek Amps was Electro Harmonix kicking around getting into the amp biz. I figure they have such a big stake in the Reflektor tube plant... why not try.
Yup. It's called micarta. We use it in the tool and die industry as an insulator between high voltage components and ground, or other tools. Usually welding equipment. It's hard, robust, and non conductive. It can also take high clamping force from fasteners without being crushed. They also make micarta washers and hollow rod to insulate screws and bolts from said energized equipment.
On the board too much brown is carbon and does lead to a short circuit. I have found that a sand blaster with glass beads is a good thing to have when repairing equipment, as it allows removal of burn marks on boards so they can be repaired. Also after done cleaning such boards it helps to spray them with glyptal lacquer, and use the clear stuff on circuit boards. That is because it helps make them like new after they have been damaged and this is the only way those boards are easily repaired when a new one is not a possibility.
What was the final plate voltage with the -77 grid vdc? The Sovtek 5881's are a 6L6GC internally, they can handle a few more than 19 watts PD. Those Mig 50's are pretty awesome amps. They basically slammed a 2204 and 5F6-A(with circuit revisions even) together, jacked up the juice and sold it for a price anyone could afford. (Wait a minute.....they just modded a 5F6A in reality🎸🤘) Regarding the transformers, I think the manufacturer only had tooling for one style bell for multiple transformers and filled the ends with material that's easy to cut/shape. Remember, we're talking about Russia here. The home of the stamped sheet metal assault rifles and hard liquor made from potatoes. Their shit just works. Another great video! Thanks!
Plate voltage was about 525V. I didn't want to push the 5881 too hard. At this bias, they should last a long, long time in this amp. And it's still loud as piss.
...and you're right about Russian engineering. Their military spec hardware is usually excellent. If it ain't broke, don't fix it. That was their motto. Well, that and "death to capitalist pig dogs". :P
Yes, what they built out of metal usually was rock solid. My dad always tells this joke about Russian engineering: Do you know how Russians build a railroad engine? They take a huge block of metal and just cut away everything that doesn't belong there.
I'm thinking the manufacturer didn't have the equipment to stamp out the cupped metal ends we're used to. Or perhaps that equipment had higher priority jobs. The ends shown there just need one of those metal benders.
better than most instructional "how to" videos I've seen in a long time...props on your playing as well. some of us non-book learnin types really pick up quite a bit more info that is usefull by watching a master at his craft rather than sitting in a class listening to some necktie ramble on for hours. very informative and has qued my curiosity wich will promt me to definately watch alot more of your vids..thanks!
I've been a sub for a while I'm just mainly a diy guy. I don't know if you've done like lesson style videos before to teach people like basics for amp repair but I think that would be really awesome I for one would love to learn more. Anyway thanks for the vids keep em comin!
No L! And you'll never hear me correct about pronouncing again. Because I'm a working man from AL. Dang!! I love your work. The way you talk us through, while showing hands on, is great for me! Thank you brother.
You do a very good job with this channel. You explain what your are doing and why you are doing it very well, plus you demonstrate the results very well too. I used to be an Electronic Technician in the Navy over 20 years ago and I haven't been involved in electronics in a very long time, but watching your channel has given me the bug to start getting back into it. I play guitar as well, so I might get into amp building. Unfortunately my electronics skills are very rusty, but you have given me the itch to dust them off. Thanks for what you do.
I LOVE comments like this! I do hope you get back into the swing of things and remain interested. Go on Craiglist and find yourself a fixer-upper amp and dig in! A lot of times you can also find stuff in the CL free section for repair. Pick up an old console tube stereo amp or old organ and get your tinker on that way too. When you get up and going, make a RU-vid video and link back here so we can see your progress.
Wow, great details in this break down, and repair. I'm sure that was one more happy customer!, and we happy viewers, thank you for the slow rig down with so much details. I learned a lot. And the dive bomb w/o whammy bar was hilarious :D
Great video series BTW, i am learning a lot. QQ, for those large capacitors you replaced, did you just cut the old ones out and solder the ends to the old posts or did you completely remove them from the old board? I am currently trying to fix my fender red knob amp and would like learn some best practices... thanks..
Awsome vids,Great info,loved your intro joke,I swear I voted :O on one of those. Have you done in the past or maybe might see in the future a Soldano head? peace.
Good video! By the way how does charvel xl 750 compares sound wise to les paul? Is it somehow similar? How do you like that guitar is it as good as people are saying. I have a chance to buy one. Thanks
With the nation on lockdown its been such a pleasure watching your vids - one after another! Your content is highly addictive making me fear the impending doom of withdrawal once the pandemic is over. I'd dumpster dive with you any day brother!
Another great video, my question is regarding that whitish substance you are using between the caps you raplaced, what is that and can silicone be used as well?
When you first changed schematics I saw v1 said 12ax7 but your first schematic said 12ay7. You caught it elsewhere though, those are interchangeable though right( not identical though)? The 12ay7 being less gainy/ less output?
Cool videos, mate. You don't have any plans to look through a (Sundholm bros. era) Sunn Model-T, do you? Or maybe, a Reval Model-T even? They're made out of Estonia and as far as I can gather, other than how it looks, they're faithful to the original. Cheers, all the best. :)
Very good video. Question concerning tubes and red plating: If your tube is red plating does it always mean there is a fault or could it be just a bad tube? What would it cost to ship a amplifier head to you from Oklahoma? thanks in advance?
Yes, it could be a tube. If it was just one tube, I would have suspected a tube first, but this was both, so I knew it was in the bias circuit. Cost to ship a head...probably around $35-$40. Right now I'm taking a hiatus from outside repairs though. Hit me up around July, I should start taking things in again around that time: bradlinzy at gmail
I have just recently discovered your channel, beginning with the Marshall head found in the trash! I enjoy your repair videos- well done! When you change components out, like pots, caps, etc- do you rewrite the schematic to reflect any value changes?
It's a silicon diode. It was an NOS one I got in some large parts haul a while back. Not sure on the model number. I just checked the voltage rating and knew it would work.
Hello brad, Im' currently working on a mig100 and it's very hard on the power tube with 540v on the plate and screen. Screen grid resistor where fried. Owner bought shuguang 6l6gc, but i don't think they will handle the voltage. You say only 5881 can survive that ? New production sovteks ? Thanks ?
I really like the tone you got from that guitar/amp/speaker cab combination t ! I'm from Czech Republic and I grew up around these Jolana guitars, since they were the cheapest solidbodies for begginers to get when I started to play guitar (late 90s). I never liked them at the time, but they kinda grew on me. Do you have any mods / tips for this model? I only remember appaling vibrato/bridge system, frets that didn't last even looking at them and horrible open back tuners
Where did you find that second schematic with all the part numbers included? I've been looking for that forever and all I can ever find is more links to the same original one by Bruce Collins.
Great info sir. Thanks. P.s. I am going to fabricate and Tolex a missing faceplate on a Mig 60. Same size enclosure? My client is upstate so I can't get my hands on it. Would you be so kind as to help me with factory dimensions. I believe it screws secure from the inside. Any help is appreciated.
Back in the 90's, I always wanted to get one of these. I came so close to getting one, but never ended up pulling the trigger. Despite their fairly poor construction, the circuits are pretty cool and placed in a nice package. it's cool that the Tube Midget was so ahead of it's time, and paved the way for all the little lunch box amps we know today.
I really like what you did on this repair! You are really inspiring me to try and build my first amp. I’m a Network Tech building servers, fixing PCs and configuring routers and such. Never really did any electronic stuff. But Mojotone has a few amp kits I’m looking at for my first build. Do you think someone with my background can pull off building a guitar amp from a kit as a first build. I’m looking at the MOJOTONE STUDIO ONE 1 WATT 2-CHANNEL AMPLIFIER KIT. I need a practice amp with low watts so, I thought this amp would be a great kit to start with. What do you think? I would really appreciate your advice...
Nice fix Brad! In Russia, the knobs go to 13 (according to the front panel)! Regarding the transformers, maybe 'folded' sheet metal was a more cost effective solution, than 'stamped' bell covers. As a sidebar, in 1975, I worked for the Canadian distributor of Hiwatt, where CSA required us to rivet metal shrouds onto the Partridge transformers to suit their regulations!
Old video so I don’t know if you’ll ever see this comment...but anyway, The input power voltage that is switchable from 110 American to 220 European, can a switch like that be installed on most amps? The reason I ask is I have two Redbear MK60’s that are 220V for the European market. I purchased a step up/step down transformer off of eBay to bump the 110volts from my wall outlet to 220volts to power them, but I can only do one at a time plus it’s a pretty clumsy set up and a pain to move around that way. It’d be nice to just be able to switch them to 110V and plug them in.
I’ve been trying to find a demo of this into a new Marshall MX412 240watt. I might just get the new Electro-Harmonix MIG50 “reissue”... Thoughts? I’m new to amp and I don’t know much. I don’t want a straight dirty amp rig since I sometimes play some ambient post-rock stuff and some looping with fuzz. A lot of 70s style spacey prog-rock stuff. I’m playing through an old Peavey 212 Classic that needs some new pots.
I have multiple devices from soviet russia with those types of electrolytics (from the 70s/80s). None of them have broken capacitors. Those caps are from 93, so they are basically new....why change them? What brand and type of caps did you put in? 530V "horrificly high plate voltage". On the screens maybe a tad high but I wouldn't bother - the bigger issue is that they have that voltage on the screens as well like all the Marshalls. These amps need a second lower voltage tap for the screens... Also, your probe does not even remotely look like it was proper insulated for the voltages you are working at.
These amps sound so bad ass. I just got one a month or two ago. All original. Looks like this one had some pots changed, but mine is as original as the day it crossed the Atlantic...Probably should get the caps changed...and maybe the pots... EDIT - btw...what does that internal trim pot do? it it a variable bias or something?
I have a Mig100 Sovtek made in Petersberg Russia. I've played it for years gigging in the US. Replaced the original tubes w/ Chinese "Sovtek" tubes purchased in the US. Never had any problems, used also in the studio for recording. This amp is a monster for those who are able to play, it delivers powerful tone and is loud. You must be able to properly set your system, just like any good 100W head, like a Marshall, etc. I love my Mig100 with the original 4x12 cab, I've had this as my main rig since 1998. Sovtek rocks!
Brad do you know about the electro harmonix mig 50 clone . Does it fix all the bugs that happen on the og mig. For 600 bucks a 50 watt tube amp seems nice.
Our "amperage" started to go up. When we talk about amounts of electricity instead of saying "amperage" the correct term for this is "current". Pardon me for making this comment but I think that a good technic like you are should refer to things by their right terms. Best regards and by the way I like the way you work and solutions you have for some problems. Thank you for making your good work public by taking the time to record and edit all this videos. By the way you also play very well.
Hello! I got a lead on one of these, but a 30watt-version, MIG-30. I bought it NOS from Russia in early 2000's.. Ten sold it onwards 2011, now asked the buyer if he'd sell it back. He said he would sell it, but it has been standing cold for the 5 last years! And as he started it up again now to try it out it had developed popping and crackling noises.. :( Would you appoint that to contact-issues, which I could remedy, or is it dryed out caps or similar I would have to have a pro look at it? ..Theres not a decent one around and I don't have car, so I might leave it rotting at the guy if it gets tricky..
sounds good.... The material you pointed out inside the open transformer ends is a phenolic insulator. They use the same material in High Voltage 3 phase switch gear breakers between the phases.
Let's hear some more fat chords from you, through that Stovetek amp. Stove, because it sounds hot! She really sounds much better than the typically fizzy timbre I'm acquainted with from those things. Did you voice it at all?
I still got a Sovtek MIG 100h. I had some minor issues with it over the years but for the price, it was well worth it. The 1/4" in/out jacks are crap and my bass pot did very little from new. Also had a noise issue that was related to the fact that it was "mishandled" during original transport, that caused the same one 5881 and fuses to blow. The amp tech pointed out the minor damage and was easily fixed. Currently going strong but Its had a bad high input jack for many years that I need to get around fixing. I just don't play it anymore. Good to see that other Sovteks are still kickin'.
That amp sounds incredible! I´m always amazed at your skills man! i dont know 1/10 of the things you are mentioning but I keep watching (maybe ill learn by watching you haha)
Cool vid again. Love your playing. The fault was a bad connection on the bias diode. When it made contact you got the correct negative bias so the anode currents were correct. When it lost contact then the bias would be 0V dc causing huge anode currents which in turn caused the B+ to drop. Must be a pretty good power transformer because a lesser one would have dropped its voltage much quicker! This amp is a good example of why there should always be a correctly rated slow-blow fuse in the B+, for this amp T500mA.
Great video Brad, as usual. However, I hope you checked the fuse. I had an old amp that i bought a while back, recently checked it because you say it so much and low and behold, not the right amp value...LOL. Thanks man! Bart
We used to have a Sovtek mig100, it was a beast and never had any issues even after years of gigging still running strong! P.S. Love the dumpster vids!
I was a dealer for New Sensor from 1989-1991,aka Electro Harmonix.Mike Matthews told me it was pronounced with a hard "O" like in Soviet.,and being the owner of the factory,I'll take his word over anyone else's.
I think it's Mica that Sovtek used in their transformers for it's insulating properties. That would be my guess as to what those panels are on the power transformer. See watching them from 5 years ago, every upload watched i have gained some knowledge that i have been able to take away with me. Thanks Brad.
Maybe next time you could play a little Scorpions Wind of Change, for the Ruski theme. Nice job figuring out that bad diode push pole board bending business.
Fiber glass board is called phenolic,non-conductive etc. Was used by hot rodders back in the day to make carb spacers. Also used in tool and die work at times.
if it's spelled "Sovtek", why would you pronounce it "both ways"? that makes no effin sense? :P just kidding, awesome videos! i play guitar myself, and love my tube amps, and while i am very technical myself, i would never go upon trying to fix them myself.. i'm glad there are people like you, and even better that you're taking the effort for us to being able to watch you fix this kind of stuff on youtube! thanks!
Sorry if this has been asked before, but is that display on your variac just one of those little cheap Ebay displays? That's a good way to use one. Nice work, btw. I've worked on a couple of Sovteks myself, years ago.
Here's where you can get one: amzn.to/2pct7kd Here's a link to my previous video where I walked through the installation: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-2mrlha-uzro.html
I bought a Mig 60 new and and Mig 50 at a pawn shop back in the 1990's. They didn't do much for me, but I've learned a lot about tube amps since then. They were a good cheap basic no frills amp. They were in serious need of upgrades as this video points out.
Out of curiosity, can tubes red plate simply because they're old? My parents have a Hammond C3 with a little JR-20 tone cabinet, and the old silver-top Sylvania 6V6's are red plating ever so slightly. The bias voltage appears to be fine (thank goodness), but the tubes are red-plating even though they're quite lightly stressed.
No. Age itself won't cause it. The tubes would either need to have a physical defect or the bias is off. Usually in old tube amps what ends up happening is the coupling capacitors attached to the grids of the output tubes are leaking high voltage DC to the grid and running the bias way off. Replace ALL coupling caps in the amp and try it again. If still not fixed, check the bias resistor coming off the tubes' cathodes and make sure the value is correct.
Cameron Jenkins Yours may be a case of the circuit being designed to run on the razor's edge of a 6v6's limits. As you may know vintage tubes tend to be sturdier than newer production tubes. A little blushing isn't always a bad thing.
Well, when I said old, I meant "well used." However, It would not surprise me if the coupling capacitors in the amp need replacing, since the measured bias voltage for the treble channel is noticeably different from the bias for the bass channel. Come to think of it, all of the capacitors probably need to be replaced, since they're all original (as far as I can tell) and the amp is almost exactly 60 years old. It's still pretty quiet, though.
nice work,, its a few years ago i see that , but still good entertaining material, its got to be the most satisfying thing to trace and fix an awesome vintage piece of kit like that then put it through hoops ,sounded damn cool,!
Micarta is that fiber board in the transformers, My uncle worked for Westinghouse for 25 years, They used that in transformers for insulation and spacers.
