Monday, January 9, 2017

1955 Fender 3x10" Bandmaster, 5E7. Yes, rare as can be.

This was a fun project. A 1955 Fender Bandmaster with 3 10" Jensen P10R speakers. This is the first original one I've had the pleasure of playing, I built one when I had my shop in Portland and sold it soon after. If I ever need to go 'big' again, I may build another one of these for myself, this may be the candidate for what I need.

What do I like about these? They are raw and primitive. They are part of the evolution to the more refined legendary Bassman amp. They don't work nearly as well in other words. The tone controls are a bit weird and the transformer to speakers is a good mismatch! (4 ohm transformer into a 2.6 ohm load!) That's a part of the sound for better or worse. Plus, I love the size. A Bassman is just a bit too big for any of my needs.

Speaking of that mismatch, you almost never find one with the original output transformer. They simply burned out. A friend had an even more rare Brown 3x10" from the early 60's and that had it's transformer replaced just like this one. I believe only Mercury Magnetics makes a proper 2.6 ohm transformer for these. When I built one that's what I used. Great part but I was a little let down. It was a lot more iron than I expected. I think they call it the "Fat Stack" or something like that. I prefer to have a smaller part, I don't need all that clear bass! So hopefully someone out there makes a trashier part now. A great sounding amp is a mixture of excellent quality parts and frankly, crap. Too much of either direction and you lose me.

This amp belonged at one point to a rhythm guitarist who played with Muddy Waters. When it came to me I saw pictures or the insides and outsides. I could see it had Orange Drop Sprague capacitors throughout, not my favorite, and the work looked a bit sloppy.

It also had a solid state rectifier and just okay modern tubes:

Once I played it other than a bad distortion (one of the speakers had a bad voice coil) I had to wonder what could I do to improve it besides the obvious: better tubes and a proper tube rectifier.

Once I opened it I could see the Orange Drop caps weren't the icky 715 type, but old polyester. I like those. They are nice and warm. You can identify them by the black stripe on the outside foil side:

Notice the blue resistors and the 2 "Chocolate Drop" capacitors in the preamp. Those do have to go. Not acceptable parts in a Cadillac!

Those blue metal film resistors are ok for load resistors, in fact they work better and are more stable. But stable isn't what were after here, we want that extra push over the cliff into special!

The only drag with modern Carbon Composition resistors is they seldom have long enough leads. So I had to extend the 2 watt cathode follower resistor:

Tone stack complete:

I use Mojo Dijon caps as these are my favorites. I also opted for a 250pf 500V silver mica cap for the treble cap. For the phase inverter I left the Orange Drop caps intact. I like them there. The Mojo caps are more like an old cap. Nice soft edges, warm. Mixed with the polyester Orange Drops I think it's a good balance.

Next was the tone caps on the pots themselves:

These were really poorly soldered. In fact the one on the treble pot simply came off then I touched it with a chop stick! You really need to have a high quality iron to get that joint right. Don't cheap out with your economy iron! Buy a Weller already!!! Also hit the back of the pot with sandpaper and use rosin. You'll have a much easier time of it and some pots you simply can't solder on to the back without sanding or using a scratch awl!

The caps themselves here don't matter as much, they are only bleeding some signal to ground, but I replaced them anyway cause, why not? The Mojos look more like the original Astron caps so....

Now the switches. They were fine, just not a classy part in my opinion. I can't stand seeing some big ass disco switches on one of these amps. It just looks stupid!

The one on the right is the replacement. I'll use the old ones for a Plexi, which likes the big bats!

Also on the standby switch I needed to add a .047@600V cap to ground. Not entirely necessary but it's in the schematic so:

And if you notice in the above photo the original wire had oxidized badly. I needed to replace that length with some nice cloth stuff as well. If I wanted to be all picky I'd age the wire with coffee, but who is going to see it???

Then the bias circuit and the grid stop resistors. I did add a trim pot to adjust bias:

Next the sexy part... The tubes. These amps sell for a lot of dough. Sovteks are nice, and I do like the Chinese 12AX7 tubes it was loaded with but, let's reach for the top shelf. Sovtek 5881 tubes replaced with Tung Sol made RCA!

Also that blasphemous solid state rectifier replaced with a NOS Sylvania 5U4 made the same year as me, 1968:

Those scuzzy preamp tubes are replaced with Mullard made "Phillips" branded tubes. And the first gain stage replaced with an RCA 5751. A bit less gain but that's what Fender wanted. Want faster breakup? Use a 12AX7, or....just turn the volume knob up!

Photos of the transformers:

The power transformer and choke are original. The output is from 1961. It's a proper Schumacher Bandmaster transformer.

And a nice chassis shot:

I did use a bigger (30uf @ 500V) cap in the first stage of the power supply. Personal preference. The rest are proper 16uf and an 8uf for the preamp.

So how did it turn out? Was all this work worth it? The amp did sound great but yes, it sounds better now. That extra color to the tone, and it's a more defined. Warmer. So I say yeah, it was worth it!

So if you own one of these, you know how lovely they are. One of the most unique American made amps that ever was produced. It's unusual cause Fender knew how to build an amp like no other, so why the mis match with the transformer. As the drive to produce cleaner tones and more powerful amps to achieve this ensued, I wonder what he was thinking with this one?

For those of you who don't have the dough for an original, I see Fender is making them again. They are pricey but not as pricey. My opinion? Pay someone else like myself or maybe Victoria to build you one. We'll do you better!


Sunday, December 25, 2016

1954 Fender Princeton 5C2 amp. Lovely warm jazzy sound.

Here's an interesting amp. A 1954 5C2 Wide Panel tweed Fender Princeton.

This was an internet purchase what was serviced by the previous owner. I didn't take any before pictures but, the amp worked fine but the work was comically sloppy. I get a lot of work cleaning up poor jobs.

The other bits: this is a really great amp. It was loaded with a cheap Electro Harmonix 4 ohm speaker and a cheap Triode Electronics output transformer. Not bad stuff, but to my ears, it was rather flat and uninteresting. It was also loaded with Sprague Orange Drop 715 caps. No, no, no. Filter caps were decent quality but sloppily installed.

So I loaded it with Mojo Dijon caps, a 60's 8 ohm Jensen C8R (I effing love these speakers!) and a Mercury Magnetics '55 8 ohm tweed Princeton transformer.

C8R: Brown is Beautiful!!!

I come across these speakers on EBay all the time. Best lil' secret though I suppose if I get more readers everyone will want one. Not useful for Champs, these are 8 ohms. But for my GA-5 and old Magnatone Varsity, it's a match made in heaven. They were often used in organs as midrange drivers so they are usually in great shape. People played polka and church music through these babies, not blues and rock n roll!

Yes I know it's not an alnico speaker. I do love a good alnico but as someone who plays out live on tiny amps, I like the way these project and hold together. I like the clarity I get. Try one! Couldn't hurt!!!

Better interior though not final:

I replaced the original 250k 2 watt load resistors which were noisy with new carbon composition 2 watters. Also replaced the cathode bias resistor and power resistors, typically they drift far out over time and these were no exception.

This particular amp has one transitional feature. They were loaded with a 6SC7 tube, then a 6SL7. In this amp the socket had an adapter to put in a 9 pin miniature socket so it could be loaded with the more modern 12AX7. This was factory. And not unusual is the tube chart simply has the 6SL7 tube crossed out with a ball point pen and 12AX7 written in. Leo Fender liked to use whatever parts he had left over till they were gone. Very much in line with his practical sensibilities.

I took out the "meh" output transformer and loaded it with a classy Mercury Magnetics FTPO-55-8. From my research on these amps, they were 8 ohms. Better to not be lazy and use your off the shelf 4 ohm Champ transformer if you are going to get this right. Just my opinion. More expensive, yes, but totally worth it. The amp came to life after installing this and the Jensen speaker. Big, warm and round. I fell in love with it right away. With a Les Paul or a big Jazz Box it's heaven.

The Mercury transformer is bigger than what was in there, and I suspect the original may have been mounted to the speaker. But the good thing, there are some factory 'mystery' holes in the chassis that mounted diagonally the transformer mounted perfectly.

These are quite different than the more sought after late 50's 5F2 model. This one is a 5C2.

The preamp arrangement is radically different than a 5F2 or 5E2. Between the first and second stage in the preamp you have a 250k resistor connected to a 75k resistor that is going to ground. It's a bit like having a potentiometer in that spot and it's set to 1/4 volume. Just for fun I tried opening this up to see if I could get more gain. The amp simply became unstable and started motorboating. BUMP BUMP BUMP BUMP.......  I put the resistors back the way they were. Looking at the schematic this may work with an additional stage to the power supply, this sound typically happens when you have a bad filter cap or too little filtering. Could go to all that trouble or...simply accept this is the way this amp is and what it is is not a later one. Why not have an amp that plays cleaner? It has such a beautiful tone. For my style, it's perfect and I kind of want to build one just for me.

You can see the evolution in this amp going from the old 6SJ7 circuit, which has little gain, to the later rock n roll nasty later 50's 12AX7 version. It sits right in the middle of that evolution. The tone is more relaxed than a later version, but has a bit more punch than the earlier version. Right now the owner claims it's his favorite. I can see having one and feeling the same way. Great little rare gem!


Saturday, November 5, 2016

Sprague Vitamin Q capacitors. Old school paper in oil magic for your hi fi!

Hello there tube amp heads.....

This is a little post about the legendary Sprague Vitamin Q paper in oil capacitors. I used to have dozens of these and at one point used to swap caps in and out of my hi fi amps when I had that kind of time. I was never all that impressed with the Vitamin Q caps in the past myself but decided to give them a go again now that I only have one system that I know quite well.

These arrived yesterday and I threw them in to my lovely single ended 45 tube amp.

When you have such a simple circuit like this, every little change makes a difference. For instance, the 6SJ7 driver tubes pictured lived in this amp for a day. They are Sylvania. Really nice tubes. I prefer my 5693 RCA Red series tubes by far so they went back in the box! The Sylvania version I love in a guitar amp. Big, open sound but for my hi fi I found them a bit harsh.

The signal caps were Sprague polyester PS type, .1@600V. I hate the 715P series that has been so popular for the last 30 years. The 716 is better but if I gotta use Orange Drops they gotta be PS types. I find them to be smooth, detailed and musical. Plus they are warm which I need and they don't sound harsh like the beloved 715.

Now the 715 in a mushy old amp? That can work. Not saying they are trash, remember, everything is a relationship so they work for some amps just great.

So when I audition a new cap, tube or transformer, the first thing I do is pick a record I've been listening to for many years of my life, preferably something with vocals. In this case it was "Rastaman Vibration" by Bob Marley. First question is how does Bobs voice sound? Can I make out the words clearly? Second is how does Aston "Family Man" Barrett sound? Does his bass sound natural.

First listen is terrible. No definition, crap bass. But, the amp had also been on a mere 3 minutes. When auditioning a cap let it burn at least an hour. When you rebuild an amp, you must give it time!

So I went about my business and came back to it after a few hours. Liquid.... That's the word I use. Bobs voice sounds clear and natural and the bass is big and fat. The bass however, does have a bit of flab I didn't notice before. These are bigger caps than what I had in there (.15 rather than .1) and I could go down to .05 and get my bass needs met. But I will continue to listen to records and see if it works itself out. As I recall, these Vitamin Q caps got better with weeks of use.

So the jury is still out. Do I spend $30 a cap on Jensen Paper in Oil? Are those worth it? (the answer is YES in my opinion. Those sound beautiful.) Or do I keep on keeping on with these surplus store gems? Time will tell and I will tell you later. For now I dig them about 85%.

And on a final note. Are paper in oil caps worth it in your guitar for tone caps? No.... Those merely bleed a little high end to the copper pipes in your walls. You can get a 50 cent ceramic to do that job. That's all marketing ladies and gentlemen......


And instant update....That was fast!

Listening to my favorite Coltrane record, "Crescent". Side 2..... I wore out my first copy ,I love this side that much.

Jazz has a wonderful way of mixing itself. At least in a quartet fashion. The bass and low drums are the lows, the piano and sax are the mids and the ride cymbal are the highs. Coltrane sounds like he's hanging out in my little apartment playing. How the hell did he get that sound is beyond me! So warm and beautiful on this record. Jimmy Garrisons bass has authority and clarity and McCoy Tyner....crystal clear. The second song on side 2 is called "The Drum Thing". All about Elvin. Such a beautiful, dark drum sound. That piece moved me to change the way I make music. Oh yeah, this is about some caps.....they've been burning in all night. I'm in love.......

Wednesday, November 2, 2016

1973 Fender Twin Reverb with rare JBL speakers

I played a Twin through high school. They're big, heavy and torture to take around. I'll never forget loading mine up in the back of my dads station wagon one night and he drove me to band practice (a Go Go band called Currency back in 1985!) and we took a corner and heard a crash. I was worried about my precious tubes. In Actuality it took out a window and the amp was just fine.....

About this amp. It's a nice one. This was a custom order one loaded with original JBL speakers and has the original foot switch.....

I'd never choose these speakers myself but when I do hear them I understand why someone would. Clean, big and bright. I actually like them in a black/silver panel Fender amp.

The complaint on this one was muddy sound, noisy intermittent reverb. It had some bad caps, needed a good cleaning, fresh output tubes and a NOS 12AT7 reverb driver tube. Never use a new 12AT7 in this position. They don't last and there are plenty of cheap 12AT7 tubes about....Sylvania, RCA, Telefunken, GE, anything but JJ or Sovtek!

This amp was also literally 7 resistors and 1 capacitor away from the original black panel circuit. I converted it. That's a part of that muddy tone one heard with these early 70's amps. It's worth it. The amp plays with a more open sound. Also re-wire the bias circuit so you can actually bias the amp. Get rid of that 'balance' arrangement.

Silver panel schematic:

Look at the phase inverter. That's where the "silverness" happens. Change it up to:

You may also change the 2 resistors in the power supply, but I prefer to leave those alone. A hair warmer in my experience.

You don't see many of these about here in NYC. Most of us prefer Deluxe Reverbs or Princeton Reverbs for these tiny clubs. So the prices are largely dependent on region. Some places you can get one for a bargain. You can buy one of these hand made amps for the price or less than a new reissue! Leaves me to wonder what the point is in those reissue amps. They are nice, but not quite as nice as one of these. Something to consider......

Idea on value:

One like this with JBL speakers can command a high price, the rest, great amp for the money!


Update on this: Client wanted a fresh set of preamp tubes as well. I'm a "if it ain't broke don't fix it" kind of guy but complied. When you change an entire set of tubes sometimes problems can arise. In this case one did. The tremolo started going 'tick tick tick tick'. No biggie. Simply put a .1 600V capacitor across the neon bulb tremolo 'bug' from the 10 Meg resistor to ground. I have little idea why this works, I'm just glad Jeff Bober showed me this trick 25 years ago! Saved me a lot of time over the years. I watched another tech painfully decline this and his customers Twin just kept coming back to solve the problem. The situation got tense. I told him this but he saw no logic in it understandably but he wouldn't even try it. I wasn't the tech at this shop and knew by suggesting this I was merely causing tension so I backed off. The customer backed off too and went elsewhere.....

Amp sounds great. Those JBL speakers have a richness to them. That's why they work so well for me. Clean but good, complex clean.

Monday, October 31, 2016

Silvertone 1434 2x12" combo. Tedious to work on but well worth the effort!

Don't have any proper photos of this one as I only have the chassis to work on. Decided to leave the cabinet elsewhere. It's a big amp and I have little room!

I've worked on many of these. I quite like the sound of them. Big and trashy!

They are a bit tedious to work on. One needs the proper approach to get them right. In this case the amp didn't work at all. That part was easy (6EU7 tube in place of what should be a 12AX7!). The rest isn't difficult at all, you just need to be patient and re-cap the thing.

When I say re-cap I usually mean change those dried up electrolytic capacitors. That part is obvious and on one of these amps quite easy. But for these amps you'll need to change EVERY CAPACITOR along with every load resistor. They are noisy. Every Sanagamo cap was leaking or dead. The tremolo was completely dead. That entailed replacing an open 330k resistor along with all the tremolo circuit caps. Also need to replace the load resistors. The 6AU6 tube was good, they usually are.

Tremolo circuit:

The 330k 'feed' resistor I'll be replacing with a 25k trim pot. Once I got the tremolo to work it was simply weak. I reduced that resistor to 50k and it's way better, but it can be great so let's go for that.

More shots inside the chassis:

Phase inverter/driver circuit:

One of the peculiarities of these amps is the filament arrangement for the 12AX7 tubes. Those are D.C. and powered from the cathode resistor on the 6L6 power tubes. They are wired in series with about 28 volts going across both tubes. The nice part about this was I have 2 modern Tung Sol 12AX7 tubes that hummed under any normal arrangement. I couldn't sell them. But in this amp with the DC filaments they run nice and quiet.

Bloody modern tubes! Got a set of modern Tung Sol 5881 tubes I dropped in this amp. One is bad....

I couldn't find a schematic so here is one that has some similarities:

Tremolo circuit is 90% identical along with the preamp....

Amp runs pretty quiet now. These will never be as quiet as a good Fender but don't let that stop you from considering one. If you get one don't bother trying to trouble shoot the issues, just bank on spending a few hours replacing every cap and every load resistor in the house. No sense in playing whack a mole with your valuable time! And please don't buy into that "but the original sound" bullshit! You can buy carbon composition resistors all over the place now thankfully, and I like those Mojo Dijon capacitors for my signal path. Get in there, get your hands dirty and get it right! Worth the effort!

I can say the same with every other Silvertone amp I've worked on. They were pretty crappy amps to begin with but that is their charm. They used the cheapest parts available so 55 years later......