1978 Marshall JMP 50 watt combo

Yes. That's all I need to say.

These are fantastic amps. This one was blowing the H.T. or high voltage B+ fuse. We had hoped it was one of the 6550 tubes but unfortunately the output transformer was cooked.

When the H.T. fuse pops 9 times out of ten it's just a power tube. Once in a while it's a shorted filter can but every so often it's the output transformer. That makes for an expensive repair. And the sad part is it does tend to hurt the value whether it sounds better or not.

Here's the ultra simple control panel. Gain, Master, EQ and presence. You really don't need any more with an amp that has this much sound. These are known as rock n roll amps but in the right hands can be good with any style. Someone clipped out one of the treble caps, the one on the volume knob. I owned one and clipped out both of them. I don't need that much treble and clipped out you can simply turn up your treble and presence if you need it.

This one has the original speaker intact. A pair of lovely 30 watt "Black Back" Celestion speakers:

So what output transformers do I like these days? I'm a Mercury dealer and I also deal Mojotone as well. For the price you can't beat the Mojo. I believe they are made by Heyboer and they are first class transformers. Friendly right out of the box. The Mercury product is expensive. Very expensive. I like there iron very much but there are only a few things to me that are worth that much more. When I was building amps for people I used their ultra expensive "Radio Spares" iron in a JTM 45 I built and always used their "Radio Spares" output transformers in my 18 Watters. They simply can't be beat in that capacity. I had the pleasure of playing my JTM amp next to a real "coffin logo" '62 model and mine was so close. I sold that amp for about $1300. The '62, granted is ultra rare, but cost around $20,000. So parts makers like Mercury and Heyboer helped me lose my lust for old amps! Why spend all that money if my intent is to enjoy it?

But for general repairs and price, the Mojotone iron can't be beat. I've used many of their transformers with dynamite results. In this Marshall I can say DYN-O-MITE! It's got it where it counts and was a relatively easy install!

JB 

Stereo Memory Man

  It's been a minute since I've written anything so I'm up late catching up.

  Just re-capped this tonight. It was making this wum-wum-wum-wum slow pulsating sound and has been slowly dying over the years. Dead filter caps. Photo after:

Nice thing about modern electrolytics is they are so much smaller than the originals. Just makes everything fit better.

These are lovely sounding units. I prefer them over the "Deluxe" version. They are built like total crap, which is part of the Electro Harmonix vibe. I've heard some that are really noisy, this one after the recap is much better now. If you open one up beware. They use this thin solid core wire that just loves to break. I only lost one and had to look at a schematic to figure out where it went. I also had to open it back up cause of a previous hack job on the delay pot. If you look at the picture you can see it,  the one in back with the blue shaft. It's really difficult to find proper pots for these with the ultra long legs, and 2 of these have been replaced. So people usually cut the old ones out and solder the new pots to the old legs. Not a problem, unless it was poorly soldered like this one! A leg joint simply broke upon re-assembly and the delay speed knob was no longer working. No biggie!

Anyway, here's a schematic.

Fun! It's been on for 3 hours now. No hum! I win!

JB

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.

Inside:

  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!

http://www.dcphotographs.com/

Happy soldering! JB

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!

JB

Philco 46-1201 "Bing Crosby" radio

  So it's the supermoon eclipse tonight. Must be why I've jammed on Iggy Pops' "The Passenger" so much the last 24 hours. "AND THE STARS WERE MADE FOR YOU AND I!!" Best rock song EVER......

   I wish AM radio didn't suck it so badly. It would be so cool if Iggy, or Dizzy, or Billie, or Hank Williams poured through my next project. Instead it's all Godawful bible thump, right wing paranoia and the occasional sports. Ok, sportscasters sound cool on this Bing Crosby radio.

 This was a fun project. It's been sitting in a bar in Queens since the 1940's. Best part is it has a built in secret 78 player.

  The crystal cartridge was shot so I had it re-built. Also needed to do a little mod to get more volume out of the phono side. And of course, this belongs to a good Tele slinger so I installed a 1/4" jack for him to jam out with. It has it's own low gain Fender Champ built into it that gives up a nice, thick rather dark voice.

  You can also use the jack to plug in your Ipod or whatever. Then you can have your Iggy or Billie or Dizzy or Hank, or your own pre-recorded Bible thump! Just be careful that whatever you do plug in is battery operated. These do not have a dedicated power transformer and cannot be properly grounded. Yup. I tried to plug in my computer which was plugged into the wall and got the Jesus shocked outta me! Serves me right I guess. Sorry bro! It's not you I diss, it's just those preachers on the AM waves!

   This radio received all new tubes and new caps with a few choice resistors since it was just plain noisy when I started. Quiet as a church mouse now. No hum, no crackle, all, um, music? Ah yeah. If you play that mean old Tele, it's definitely all music!

JB

Korg Voica midi out mod

   Here's something completely different. I enjoy the occasional 'never been interested in this before' job. They can open my mind. This particular job was simply following someone else's instructions. It was to install a midi out to make this thing a bit more (actually much more!) useful to my friend.

  The instructions are really straightforward, and the wiring part is really easy. But like many mods, if you lack experience they can turn into a bit of a nightmare. You need to improvise a bit. In this case the new jack is quite a bit too tall and there is little room for error in placement cause, well, there is little room at all!

You can see in the top photo, it's the shiny new jack on the left with the 'Jef Brown' special brass screws for extra class. The instructions tell you to use a 1mm guitar pick cut as a spacer between the jack and the housing. With the jack provided I needed to cut up 2 1.5mm for a total of 3mm. And still I needed to bend the tabs. You can see it in the 2nd photo. One needs to bend carefully or you may wind up breaking the tabs.

 Here are the instructions for this job:

http://www.marcushamblett.co.uk/volca-keys-midi-out-mod-step-by-step/2015/04/04/

  If you don't trust yourself to do this, pay me $75 and I'll gladly do it for you!

  My friend sent me a video of this in use. It's really fun! These little things no longer fall into my 'never been interested before' category. I can see myself losing hours in this world of fun little machines! I want......

JB

Traynor YGM-3 combo. The Canadian Deluxe Reverb?

These are terrific amps and thankfully quite under rated. They can be had cheap. Similar to a Deluxe Reverb but more of my flavor: EL-84 output tubes for that more "British" sound, better tremolo and more of that wild man reverb than the more refined Fender amps have. So wild that they can run away. A couple simple mods can tame that. In this case I just added a .002 cap from the reverb return to ground and bypassed the 1 meg pot with a 1 meg resistor. This maintains the more crazy and trashy reverb without making it too tame.

Other than that the amp had a crackle and hum problem. Solution was easy: at some point one of the output tube sockets was replaced. The tech put an old socket in but failed to remove the tarnish off the solder points. It had 4 cold joints! So I removed the wires, hit the points with some sandpaper and re-soldered. Problem solved.

Customer loaded this with some fresh "Mullard" EL-84 tubes. They seem to work in this amp just fine. These amps tend to run hot. Most EL-84 amps have about 300 volts max on the output tubes, this one has 398 with each tube running at about 30ma. Nothing is red-plating and it sounds great so I let it be.

Here's a shot of the inside. Built very much like an old Fender amp! Very sturdy, very high quality....

I also changed the electrolytic caps on the circuit board. Someone replaced the ones in the bias circuit but did a sloppy job so I took care of that. The big filter cans can be changed at this point but I left them. Amp runs quite, hum free. Changing the ones on the board cleaned up some crackly stuff.

Notice it's loaded with those lovely Mustard caps. Mmmmm. Yeah, I'm a big fan of the old Traynor amps.....

If this were my amp I would probably change the tone stack myself, maybe set it up like an old Marshall by adding a cathode follower circuit. I recall doing that a long time ago for a client and being really happy with the result. But, I can get used to this. And hearing my client play it, he sounds better than I do naturally. This is his amp and he knows how to work it!

JB