Maestro Envelope Modifier

 

Ok, I know it's not a tube amp but whatever. It's old, it's vintage and it's effing weirdly kinda cool.  

I've received a box of pedals from Southside Guitars in Brooklyn. Pedals are not my idea of a good time but I do like bringing things back from the dead. 

This one arrived DOA. If you are lucky that just means a bad battery cable or a bad joint. You should also heat up EVERY solder joint and clean every pot twice minimum. Did that and still nothing.

In this case I needed to change the Optocoupler to get it going. I bought one and the thing made sound but did nothing else than that. I also re-capped the thing, still no effect. I was at a loss as to what to do. So I consulted the interweb and found a guy on the Facebook who had success with one of these. I followed his advice and made my own optocoupler with a white LED and a GL5528 photo sensitive resistor.

(Shout out to Pete's Pedals in St Louis for the help!!)

And, it started to do, erm, something! I needed to re-solder the batter connectors on both ends of the cable and clean the pots once again and now it works. I needed to adjust the little trim pot on the inside to make the LED maximum bright. The cool thing about making your own optocoupler is you can see how that light is actually behaving.

It's a very rare box with good reason..... not much use for a guitar player like me. I can pretty much make my fingers do what this does but I can see one of my analog synth addict friends having a good time with this box. You play it softer and it lets more sound through in one mode. Play it louder and it cuts the volume. That's in Bow mode. Percussion  appears to be the opposite. You hit the note hard and it really spikes. 

Can't really tell much from my little demo but here we go anyway......

1965 Fender Vibro Champ Amp, low volume, What are some people thinking when they mod an amp????

 

This was a repair amongst many I did for Southside Guitars last month over a marathon 2 day period. Simple amp, somehow it took up more bench time than the rest!

You're looking at a run of the mill used 1965 "Fender Electric Instrument Company" pre-CBS Vibro Champ. Lovely little buggers. The first time I ever played one was at this guys apartment in the 80's in Boston. He used a TS9 Tube Screamer into it to record my guitar tracks when I was a Berklee student. I was pretty floored at how good it sounded. I think he had a reel to reel or one of those cassette 4 track machines we all had in those days, the Fostex X15 or Tascam something or another. 

Anyway. This one had very little volume. I popped the chassis and, well, you tell me what you see:

Yeah. Seriously. What the eff? That nice bit of lamp cord poorly soldered between the input of the volume knob directly to the 15k midrange resistor which goes to ground. So where you want to see up to 250k between you and ground, you get 15k maximum. I just don't understand what they were trying to achieve here! Did they put it together and say "Yeah, now that's the ticket to Hollywood baby?" 

Why didn't they just undo it? Ugh......

That was the first thing to take care of and while it helped tremendously, there were plenty of other bugs.

Always start from the back and go forward. The speaker was an old alnico full range 8 ohm job with a whizzer cone. That wasn't helping any so I just threw in what we had that day, a reissue 4 ohm used Jensen Alnico speaker. That helped but still, meh.... blah.... lackluster. No bass at all.

They had replaced every single signal capacitor with used / leaky weak caps that were also the wrong values. I used Mallory 150s and if you notice, I grounded the amp and used the .047 "Death Cap" at the midrange capacitor cuz, why not? Reduce reuse recycle! And those never go bad and have a special sound. 

I also replaced the tremolo caps with fresh ones as that was super weak and they had some weird stuff going on in there too. 

But still, no bass and pretty sad tremolo.

Cathode caps..... no bass, sad tremolo. Tremolo is just an LFO right? Better have fresh cathode caps to get it strong. In fact, just replace them already! This amp is 56 years old now.

After that I still wasn't happy though. Tremolo was working albeit, just not awesome, and the bass would vanish when you turned the treble up. Weird......

So upon closer inspection I noticed the tremolo intensity pot was dated 1966, but no indication of the ohms. They always say 25K RA. So I pulled it and measured the thing. 500k. WRONG! 

I dropped in a 50k pot since that was all I had on the shelf. Those 25K reverse audio pots are hard to find. The 50k pot isn't correct but it did make the tremolo work better. With the 500k pot there was almost no tremolo until you got up to about 8. So, while not satisfied this would work. I could also bypass it with a 47k resistor to make a fake 25k pot. I don't like doing this but in a pinch it does work and only the rabid amp fanatic can usually tell.

But that treble control bit was really driving me bananas. The amp still seemed weak too. So I then figured if the Bozo that modded this amp changed that tremolo pot to something so wack, maybe they changed a tone pot.

They didn't. The tone pots are the original 250kA pots dated 1965. 

So I checked the volume pot. Lo and behold, it was the 25K RA Intensity pot I needed! Captain "Wha? TechNo No No" used the 25k pot and scrapped the 1Meg pot that was in there. I took that 25kRA pot and put it where it belonged and threw in a new CTS 1 Meg volume pot. 

Now we're cooking with grease...... GREAT tremolo and GREAT tone!

The power transformer was replaced sometime in the 70's with the correct part. I did clean up the wiring there too. Come on folks, twist those AC lines already!!

In conclusion. I do not know what this person was trying to achieve with the mods they did. If they were trying to make the amp play with little volume, why not just turn the volume knob down? I imagine they may have been trying to get more tremolo so they used that 500k pot. Nope! 

If you do not know what you are doing then please consult someone! Otherwise a fella like myself can spend hours undoing your ill conceived ideas. Seriously, ask. Most of us are happy to share information....

J

Plush amp circa 1969 baby!

 This is from the pile o' bigass amps at Southside Guitars. 

Not going to get all technical, nothing new to write. I just wanted to share some photos of this behemoth!

This was a "just get it going" job. It didn't take much. I just replaced the electrolytic caps. Fortunately that quartet of beautiful GE 6L6 tubes was in great shape. Most of the preamp tubes were good too. I replaced the first stage filter caps and one of the new ones was bad! 120 cycle hum and low b+ voltage around 380 or so. Good indicator it's the first stage. Replaced it and voila. 

How are these amps? They're like a janky ass Fender that looks soooooo glam. Made well enough and not one bit better! I've worked on many including the "Earth" amp series built later. They were made in NYC. This one boast a 2x15" cabinet. I cannot imagine anyone in  2021 being interested in hauling one to play in sad backroom gigs where they have no chairs but 200000 watt PA systems that sound stellar, but please, someone start a band with these as the backline so we can see a real film, no filter photo!

Tremolo and reverb are good and lush. Get yerself a fuzz box and a wah wah and write yourself the ticket to the sun baby!

The hardest part about working on these amps is getting the chassis out of the head box. There's literally no room at all! I always wind up pulling the power tubes out then taking a dead blow hammer to knock out a piece of wood that holds the back grill in place cause it is dead in the way of your power transformer! 

So if you come across one, re-cap it, bias it and test test test it before you put it back in the box. It's like a forest grows around the damned thing minutes after you box it up and if something is wrong, a gotta open it back up again!!

Go big kids! You have strong backs still!!! And big amps are kinda cheap these days!!!  

J

1967 Ampeg B15N 2x15".... rare bird!

 Just had a day servicing two huge amplifiers made in the day of, well, huge amplifiers. 

This may easily be the coolest amp I've ever seen from Ampeg:

I believe this may have been a custom order. It's a later model, with 7027 tubes rather than 6L6, and a 7199 driver tube. Grid bias, 5AR4 rectifier and those lovely 6SL7 preamp tubes. The tweeters are a cosmetic addition having never been hooked up. 

Not going to get into anything technical, I just wanted to share this behemoth with y'all.

The cabinet has that ultra cool Austin Powers era cosmetics. I have a friend who has a single 15" version as well. Big amps really are no longer in vogue in NYC. This one was on the Reverb cheap as chips and still sitting there. Today the world is about small amps and efficient PA systems. I mean, who wants to move a refrigerator every time you have a gig?

That being said, if I owned a little coffee / wine shack where I featured jazz and folk music, it would be kinda against the law not to own this and stick it in the corner next to the house Slingerland drum kit.

One interior shot:

I did grow up in the last age of the big amp. I used to play a Marshall half myself. Can't say I miss moving these things but, damn. Nothing sounds or looks as cool as that oversized backline!

J

 

My favorite amplifier was stolen, please help! Magnatone A-646

 Hi all. About 2 weeks ago my favorite little amp was stolen from me. The photos here are from about 5 years ago and it's more beat up now. I also replaced the knobs and the pilot light which it sky blue, smooth glass. 

Any info would be much appreciated. I've filed a report with the NYPD......

Thanks! 

Bronson Amplifier circa 1949, in the original box with the matching lap steel

 Today I got to see a stunning piece of history. This Bronson amp dated 1949, still with the original shipping box. It spent some of it's life in New Mexico at the Aloha Conservatory of Music. Apparently this school was affiliated with the Bronson brand. I would love to know more! American musical instrument manufacturing is a fascinating subject for me. Especially when it is tied to schools. 

Nothing to really write here, the amp isn't NOS, but it's as clean as one can be for a 72 year old amplifier. The customer wants to use it so sadly I needed to change every capacitor in the house. All of the wax caps were leaking badly (yes even with little use, they likely leaked right out of the Valco factory!). And I also replaced the electrolytic caps and the power cable at the customers request. Easy job. These are so well made. 

So the insides are all "before" pictures for your amusement. 

How does it sound? We happen to have a lovely old Kalamazoo model A with a real Charlie Christian pickup. Lovely combo. I'm a fan of a good field coil speaker which this has. Nice low end.

The filter cans are as follows: 40uf (big for the time!) and a dual 10uf can for the preamp and screens. 

Tubes are 5Y3, 6V6 pair, 6SC7 phase inverter and 6J7 pentode for the preamp. I'm a big fan of this arrangement having built a few amps with a 6SJ7 preamp into a 12AX7 or 6SL7 phase inverter. Big, warm sound with nice low end. 

Valco knew how to build a good amp. This thing runs pretty quiet. And it's a nice thing to look at. Easy on the eyes. An amp should be able to double as furniture so it doesn't get stuck in the closet when not being used. Potted plants should go near it alone with your sofa. These manufacturers had style back then. Not an ugly rock box or just some industrial looking thing that belongs in the garage. This is something you want to relax with and play some sweet music through. 

J 

Kalamazoo KEA Amp revisited. "Why didn't I think of that???" Bad fuzz in the sound, let's get that out with a mod.....

 The Kalamazoo KEA amp now lives with my good friend Eric. It's become one of his favorite little amps to work with. We both think it's special sounding, very rich and clear. But alas, it still had some annoying issues.

This amp initially was a basket case. Doomed to the "part it out" pile. Missing speaker and all. I wanted to save it so luckily I found deep under the bench at Southside Guitars an old ceramic square magnet 10" that was shallow enough to fit in there. I replaced the field coil, with a 1k 10 watt resistor and yadda yadda, re-cap blah blah the usual.

In the end it became a lovely sounding amp. Impossible to make a buck off it so thankfully Eric wanted the thing. 

The volume pot was scratchy so I replaced that. The schematic called for a 500k, but what was in there was actually a 1 meg. I used one of those to keep the integrity of the amp. You need to remove the power transformer to access the pot! Easy enough but it's one of those things where you realize what a genius Leo Fender was! 

The pot was worn out but so was the .05 cap feeding it. That was leaking causing some scratchiness so I replaced that. He was stoked cause the pot was getting worse and worse, it only worked in certain positions.....

But it still had some rattle issues. Most were easy: microphonic old RCA 6V6 and very microphonic 6SJ7. Piece of cake!

But then I get that call..... something in the background sounds like a Fuzzface when it's out of batteries. The decay is like an amp that is biased way too cold. 

I was praying it wasn't the speaker. We paid good money to have that dead old speaker rebuilt....

So first thing was I re-doweled all of the screw holes. Some were loose after 70 years. That helped. The chassis was vibrating. 

But not 100% which is what we're shooting for.

So I figured let's lose that metal speaker grill. These amps likely weren't turned up to 10 back in the day. Those metal grills can cause issues. And we'll replace it with a boss looking vintage grill cloth. This amp sells for less than $500 on a good day so before you scream at me for changing that grill, I'll just say I DON"T CARE! And neither does Eric. This is an amp being used by a pro......

Anyway, that helped! Buy that decay was still bothersome. It didn't happen all of the time but it was annoying when it did.

So, next was more cabinet work. I mean, why didn't I think to glue that big ass crack in the baffle???

Done! Helped! Not perfect!!!!

So at this point I'm ready to throw in the towel. I sat down to lunch and had my Kabab Shack platter (Damn they are good there! 10 year customer!!!) when I had a thought:

On 70's Champs I always remove this one little capacitor that they added during the CBS era. It's a 330pf cap going from the control grid (pin 5) to the cathode (pin 8). This shunts some of the very high frequencies to ground, taming that sine wave if you will. When I worked for Budda we had a similar thing on the plates of the EL84 tubes to ground. 

Some Champs I wound up putting it back in. Others not. Why replace it? On some Champs I got this ugly distortion, not unlike a Fuzzface with a dying battery.......

CBS sucked but they did a few things right.

So after lunch I did two things: 

I added a 1 Meg resistor from the center tap of the volume pot to ground making it effectively 500K. I figured the schematic had a 500k for a reason. It's also not unusual to see values vary on amps this old. The pot was clearly original to the amp.

Then I also put a 100pf cap across that resistor. 

And..... that did the trick! No more nasty distortion getting in the way of Eric's playing! And on top of that the amp just has a warmer tone. It didn't lose any volume or any bite for that matter, it just simply works better.

So now this "one foot in the grave, another on a banana peel" amp is ready to cut tracks. I didn't think I could like this amp more than I already did. 

J