Monday, October 12, 2015

Sovtek Mig 50 Midget: For Steven Melkisethian.

  Back around 1991 I worked for Angela Instruments in Annapolis Junction Maryland. For those of you who don't know Mr Steve Melkisethian he was perhaps the biggest vintage Marshall dealer in the country who dedicated much of his time scouring the British countryside looking for old English amps and hauling them back to the states. He did the same here much to the jealousy of other vintage dealers. Dude worked harder than anyone and served as a huge inspiration for me teaching me much about old tube amps and how to build new ones as well. At one point he even published a Xerox copy of all his haunts across America (army mess halls where he bought tweed bassman amps they were using for PA systems, pawn shops, crazy collectors etc) that you could buy for $300. Steve is perhaps one of the most brutally honest men I've had the pleasure of knowing. He doesn't hold back. When the vintage guitar and amp business got too sleazy and gross (fake brokers, drug money buying Plexis) he stopped messing with it and scoured the Maryland landscape for vintage Hi Fi. You could buy Marantz 8B amps at yard sales for $25 and sell them to Lenny Kravitz for $1600. See, the country where you are from, people don't appreciate what they have until a foreigner does. Look at the Chinese paving archeological digs over with cheap shopping malls or the British giving away old Voxes (Steve bought 2 AC-30s from a clothing shop owner for thirty quid once! And he even told me about a dealer in England who burned vintage Marshall cabs for firewood! There was an over abundance of this stuff around!) and here in the US we were willing to throw away old Heathkit, Eico, McIntosh and Marantz and buy Sansui cause it was new. Steve saw the value and put the kids through college. "Turn that trash into cash" he said once. We would get phone calls from folks who were pissed off cause they sold that high quality wonder for pennies. Hey, not our fault. You failed to see it's true value.

  It was around this time when the USA stopped producing tubes. The Reagan era. The Berlin wall fell down and the nuclear threat was no longer. Why were we still making tubes? Cause they can handle high doses of radiation. Our radios could potentially still operate. So the threat of an atomic ending went away and so did a whole industry. A happy day for the world, a sad day for a lot of glass blowers, grid winders and plate stampers.

  We started buying tubes from Russia. We needed them. Making tubes is a nasty, toxic business and Russia has looser laws around poisoning the environment. I was one of the first at Angela to buy a pair of Sovtek 5881 tubes for my Super Reverb. Oh, they didn't sound as delicious as my old tubes, but they were tough as hell and cost me a fraction of what Groove Tubes was charging. It was actually an exciting time. Buying old world technology from the old country.

  Angela was the first to get a shipment of Sovtek Mig 30 heads. I bought #32. Sounded freaking great, especially for a modest $200! (Keep in mind, Steve was selling ugly original JTM45 heads with maybe a transformer changed for $750 on up! I was just too cheap and broke to go for it!).

  #32 lasted a few gigs then it blew up. Fried output transformer. They didn't really have it together. But that sound was great. Perfect blend of a Black panel Bassman low end with a Marshall top.

  I was given #8 since the first was still under warranty. Didn't sound nearly as good so I sold it. Cool thing was they looked entirely different from each other. They were still working on a 'look'.

  They got better over the years. I've worked on many. This was the first time I've seen one of these:

Lovely wood cabinet and BRUTAL sound. They aren't at all like a Marshall to my ears. More like, well, pure fuzz. Psychedelic soul dig baby? These aren't the easiest amps to get around in and the transformers weigh a ton. I have a 50 watt Marshall up next and it's significantly lighter.


  This one came to me as weak, please re-tube it. Turns out that wasn't the problem. Oh if I was a dishonest man I'd make the rent easier! In this case I just needed to clean it thoroughly and re-bias it, tighten up the horrifically cheap plastic jacks and send it on it's way. The preamp tubes are JJ, the power Svetlana. My client says it's performed 150 shows with no servicing. Tubes are still a close match and it's loud as a damned bomb!

  What was the real issue? My client says she just bought new cables from (biggest cable company you can think of with a lifetime warranty). My guess? It's one of those cables. They are notoriously bad even though they are expensive and have great marketing to help them sell. You may ask me which company but you've probably already guessed by now. I won't say lest they sue me. That's the way big company America works. Sad but true. And that is one of the most inspiring things I'll take away from working with Steve. He was unafraid to take on big bullshit. We had the occasional threats and folks selling snake oil hate an honest man.

  Lordy. Imagine if we all possessed that kind of candor. We'd all be a lot better off!

  Anyway, if you like your amp loud and cheap, seek one of these babies out. Oh, and here is a schematic. 4 gain stages before it hits the tone stack. Amazingly enough, the tone knobs are more responsive than any Marshall!

I should mention, Steve, his wife Sue and I all share a love for the camera. Here's their photo website. Some pretty damned good shootin' here!

Happy soldering! JB

Friday, October 9, 2015

Ampeg Gemini G15

  Here's a great 'bargain' amp, an Ampeg Gemini G15.

Ampeg amps are not my favorite to work on. They are a bit of a pain in the amp. A lot more screws to unscrew, and you need to navigate the layout which is awkward. I usually put it up on it's side and do some involuntary yoga moves to remove parts and replace them.

One side of the boards and the other:

Also if you consider buying one, the tubes are uncommon and often expensive. This one originally had 7591 tubes which were lovingly converted to 6L6 tubes. I think Main Drag did the work and they did a great job. Makes my life easier when a good tech is there before me!

These also have the very hard to find 7199 as the phase inverter/driver tube:

This one is good for now but it is starting to show its age. I burnished the pins which helped reduce noise but soon enough it's going to go. It does have a bit of hum but not enough to cause alarm in this psych rock machine.

The 7199 was developed by RCA in the 50's from what I understand. An old tech once told me: "The 7199 was never a great tube, it was made by RCA so RCA could build circuits around them so people would have to buy them!" You find them in the legendary Dynaco ST70. There are plenty of other friendlier pentode/triode tubes like the 6AN8 or the 6U8. I've converted a few before with very pleasing results. The good news is you can buy 7199 to 6U8 adapters for cheap, and 6U8 tubes can be had for a song!

  So this amp came in cause it was noisy. The volume pot on channel 2 was so scratchy you could no longer use it. I noticed both volume pots were changed so I looked for culprit #2: leaky coupling caps. Bingo! Replaced the 2 feeding both volume pots and their old 270k 1/2 watt resistors with new ones. Also noticed a burnt power supply resistor. It was working but charred really badly. a 470 ohm 2 watt resistor. I replaced that with s 5 watter. It'll never die again.

  Here's what a burnt resistor can look like:

  Last bit was to fix the reverb. Simple fix, the tank wires broke. I see this all the time. I'll keep splicing them until the tank really dies. I hate to replace these old tanks cause they have their own special sound to them. So I did my job for Mother Earth keeping one less object out of our landfills today!

  Now the good stuff. These amps sound incredible. Really fat and warm. They are the answer to the Fender Deluxe Reverb, about 25 watts into a single 12" speaker. Plus you get the futuristic name. Ampeg really embraced the 50's space race hipness. While Fender had names like "Princeton" and "Harvard" Ampeg had the Rocket, Reverb Rocket, Gemini....... I think Gibson had the Atlas but that's another story.

Update 9:33pm 10/9/15...

Wasn't convinced the 7199 was the hum culprit. I was right. It was a filter cap. It was a replaced filter cap, an 80@450V. I've seen techs use these before. Military sealed Spragues that are gold and New old stock. Trouble is, even if it is NOS it's still just an old electrolytic cap. Don't use them. Go for fresh stock. Amp is quiet as a dead fish running idle now!