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

The coolest lil' guitar amp ever made. WHO MADE THIS????

This is easily the most adorable amp that's come across my bench in my entire career. I don't know who it was built by, I just know it was made during the 1940's. It's a 3 watt amp using a single 6V6 driven by a 6SF5 triode with a 4 pin 80 rectifier tube. This drives a 6" field coil speaker. It was brought to me in good working order but the client wanted more breakup. It had none at all. Just a nice mellow voice. He also wanted a switch pot (it had no on/off switch originally, nor did it have a fuse holder!) and a line out to drive a bigger amp.

So basically I re-did this amp more like an old tweed Champ. I replaced the 6SF5 with a 6SL7/5691 dual triode.
Here is the original ultra simple preamp circuit. No cathode resistor, single MASSIVE 300k load resistor and an old wax .01 cap.

First step is disconnect everything except the filament wires which are the same for the 6SF5 as they are a 6SL7.

I also removed the 500K pot since I'll be replacing that with a 1 meg switch pot.

Next add in whatever will be closest to the chassis, in this case the 220k load resistor on the 6V6 and the new .022 cap feeding it:

Now add the pot. Notice it is turned a bit sideways. If I had it straight the lugs for the 117VAC would be dangerously close to some of the pins on the 6V6 so, ya do what ya gotta do!

Once the pot is installed you can build the circuit around it quite easily...

I like to use this fiberglass tubing called 'spaghetti' that you can buy from Antique Electronic Supply. It works like a charm and actually looks rather correct in a vintage circuit. They used to sell it in black but I don't know that you can get it any longer.

When doing a mod like this you never know how it will turn out until you play it. You may need to do some tweaks. The original circuit was ultra quiet. When I fired this one up it was quiet as well but when you turned the volume up it started to do this motor boat oscillation thing. BUH BUH BUH BUH in rapid succession. Easy fix. I merely needed to add another filtering stage. This amp originally had 2 filter caps and the plate load resistor for the preamp tube came off the screen grid of the 6V6. I added a 56K resistor there into a 10UF 500V cap. Oscillation gone.

Motor boating, as that oscillation is called, usually shows up with a faulty filter cap. I did once have a brown Princeton amp that had this issue and the only thing that fixed it was adding another stage. That customer had 4 of those, all sounded great, but the one had that issue. I figured it out by looking at later Princeton amps. They have four filter stages, one isn't actually being used. The brown amps have 3 just like the tweed ones do. I figured the fine folks at Fender must have started adding this stage cause it was a problem for some amps though most were just fine. So if you have a brown Princeton and it has that issue, and you've re-capped it already, you're not crazy. They were evolving at that point into what they became and they hadn't worked all the bugs out.

So how does this sound now? Tom Waits comes to mind. Like a fat radio. It's only a 6" speaker, and it's a field coil speaker at that, so it has a nice warmth to it. It now breaks up nicely and if you want it clean, merely roll back the volume on your guitar. It still retains it's sweet original voice this way, just now you have somewhere to go. If I had to venture a guess I would think this amp was built by Magna /Esty in California. It has that nice mother of toilet seat covering, pearl colored too. But really I do not know who made this amp. If you do, tell me!

Happy amping! JB

Wicked cool Deluxe Reverb on Ebay. BUY IT!!!!!!

This was one of mine. I don't remember it but I'm sure it sings. It has the nice Mogami hookup wire I used to get. Whoever buys this amp will be one happy camper!

Ebay link: http://www.ebay.com/itm/291506543581?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Carr Rambler, weak tremolo!

Here is one of my favorite modern day amplifiers. A Carr Rambler.

They are inspired by the well sought after Fender Princeton Reverb but this company has some pretty different things going on. I admit I've never been a huge fan of the black and silver panel Fender amps, too icy for my taste. I prefer tweeds and old Marshall amps. But I always dig the sound of these amps, largely because they are cathode bias rather than fixed. What this means as an owner of one of these is you don't need to bias the amp, feel free to drop in whatever 6L6 tubes you want. No trip to the shop necessary. What it also means is the tone is ultimately much warmer. These have that lovely magic midrange I need from an amp.

They also use Solen polypropylene capacitors for the power supply:

 They are huge and you will never need to replace them. They have the added advantage of giving the amp a smoother tone overall. Electrolytic caps are the 2nd from the worst, tantalums are at the bottom. The fact that Carr went this far to make a boutique amp truly boutique is impressive. I myself like a mixture of high quality components and trashy components. These don't use anything special in the signal path, just good old Mallory 150 series caps. I like those myself.

Here is a shot of the chassis:

Truly hand wired. A lot of love goes into making these amps. They are shockingly quiet amps. I could barely tell it was on until I played some music through it.

This came in cause my customer thought the tremolo a bit weak. Yeah, I agree. When I get a Princeton with a weak tremolo I usually check the resistors and caps. If they are all good then I replace the 1 meg resistor feeding the intensity knob with a 470k or lower. Tricky part is to get it strong without too much "wump wump woof woof" sound coming through. This amp has a very similar circuit except that it has no resistor. It is indeed a bit weak. So I replaced the 100k load resistor with a 220k, that helped. Next I put a .22 cap in parallel with the .1 cap that is feeding the intensity knob. To tame the  "woof woof" stuff I put in a .022 cap from pin 6 (connected to 220k load resistor and feed cap) to ground.

Also replaced one crackly 12AX7 and replaced a weak reverb driver tube with a nice NOS 12AT7. I never use new 12AT7 tubes as a reverb driver. They can die fast and there are plenty of very high quality NOS ones around.

Thanks for reading today! Feel free to ask for more specifics if you have the same issues.

JB