8/16/17 Magnatone Model 108 Varsity Deluxe

I love Magnatone amps. Just a great, warm sound all around. I've worked on dozens of Varsity amps, but not the Varsity Deluxe. Completely different circuit, more like an early tweed Princeton. I do own a Magnatone Model A646 that is similar to this amp circuit wise except it uses a 6SL7 rather than a 12AX7 for the preamp. This amp loses the Hawaiian theme, a move from the 40's to the 50's. Classic Jet Age style.

Typical single 6V6 tube with a 5Y3 rectifier and 12AX7 preamp. 5 watts, 8" speaker....

Grounded it, re-capped the power supply, fired it up for the first time in probably more than 2 decades (pulled from an old studio that had 100 amplifiers in various states of neglect 17 years ago!).

Sounded like crap.......

A little secret. The ceramic caps in these can sound terrible. Just change them. These amps aren't worth much so why have 'originality anxiety'? I replaced them with some Mallory 150 caps and the amp came to life. It sounds fantastic. Punchy, good volume, lots of warmth and harmonics.  Great jazz tone with mild breakup. The earlier Varsity amps had great signal caps. If they are still working I leave them alone. The later ones use those lovely Ajax blue pill caps that Fender used. But these? Pure crap. Trash them and enjoy your amp! These can hold their own with any other small amp from the era. Transformers are excellent and the speaker is a nice little Jensen. Worth re-coning if it's fried.


-JB

8/15/2017 Three Ampeg B-15 amps, one week!

Simply put, the Ampeg B15 is a legend of the studio. This plus a Fender Precision Bass plus massive amounts of talent and persistence equals the legendary Motown sound. But, any passive old school bass sounds great on one of these. I've had the pleasure of working on many of these. This week offered a nice journey into 3 versions of this lovely amp.

First a 1963 model:

This one came from MSR studios in New York City. Countless artist probably recorded through this amp including the Stones, Talking Heads, Roberta Flack.....

This was the best of the 3. It's an early cathode bias version. Probably in the 25 watt range. What do I like about it? Punchy, great low mids, clear sound with a nice bit of growl.

This particular amp was sitting neglected for over a decade. It was a hot mess when I got into it. Random wires clipped, some components flopping about and the tag board burnt through where the cathode resistor resides. Typical, that resistor gets hot. Something blew up in this amp and the power transformer was also fried. This is typical too. I replace power transformers in about one of these a year. This year it's been 2 so far. Weak part I suppose. I didn't need to replace any of the Cornel Dublier caps, they are almost always still good. Surprisingly the circuit is dead quiet with all of the original resistors as well. They didn't mess around with making things cheap back then.

After replacing the power transformer and re-capping the power supply it roared back to life. Glad to say it's making music again in another studio. I'm stunned anyone would let this one just sit unused for that long. The tone is simply perfect. Loud enough for a small combo live too. But best suited for studio tracking.

The next one is a 1966 model:

Similar cosmetics, the differences are it's now a printed circuit board rather than the old school tag board. Ampeg did these so well that it's still fun and easy to get around in. It's also fixed/grid bias rather than self/cathode bias. Result is more power, more headroom, more 'clinical' sound. Haven't dug into this one yet but will be re-capping the power supply.

It doesn't hum so why re-cap it? Isn't it best to leave it original?

Short answer: no way. Just do it. Why?

First is safety. This amp is 51 years old. Caps fail. You don't want this happening.

Second is sound. I can always tell and feel the difference. Stronger low end and more even across the range. My clients agree. Most of them spend years listening carefully in the studio and they say the same thing. Amp got 'bigger' sounding.

Right now the amp sounds good, but we're going for great.

Amplified Parts (CE Distribution/Antique electronic Supply) makes brilliant caps for these. The grid bias amps require a 525 volt can and they also have a beautifully made 25uf@800V "firecracker" cap for the first stage.

Here's your can:  https://www.amplifiedparts.com/products/capacitor-ce-mfg-525v-404040uf

And your firecracker:

https://www.amplifiedparts.com/products/capacitor-ce-mfg-800v-900v-surge-25-f-electrolytic

The firecracker cap saves a good amount of time on installation. I used to use the Sprague Blue Atom 20@600V cap, but you need to monkey around with stuff to make that work. These come with a wire tie and easy mounting. Takes a whopping 60 seconds to install.

Oh yeah, order this too:

https://www.amplifiedparts.com/products/insulator-4-section-fp-cap

Spend the extra $1.95. It's worth it.

Next photo is one I worked on last winter. It's a 1968 model. Similar 'drip edge' cosmetics to the Fender amps of that year. Pretty much the same amp as the '66 but with a new sexy look. Great amp.

I needed to replace the power transformer on this one as well. Full re-cap of the power supply. Powerful. Great live or studio rig.

The 3 amps above all have the original CTS speakers loaded into them. Still making music!


Last but not least is an early 70's model. These are great live amps and are a bargain:

This one also came from a studio that let it rot away. Didn't take much, power supply re-cap, new preamp tubes (6SL7) which were all dead. I left the signal caps alone in this one as well. 1/2 are the Cornel Dublier green pill types, the preamp is loaded with the turquoise little fish caps. 2 of the input jacks were opening up so with nothing plugged into the amp it squealed like a electric hog. I've seen people re-cap amps and go to all sorts of trouble when all that was needed was a good closed circuit Switchcraft 12 jack.

These late model amps have nice but not really necessary filter switches for 'ultra low' and 'ultra high'. These share the most similar sound to the SVT out of all of these, probably due to the preamp. More of an analytical sound than the amps above, less warm but still plenty of warmth. Not nearly as attractive, which is typical of the 70's designs over the 60's. But, this is the best live amp choice. Lots of power! This particular amp was loaded with an Eminence speaker and is now slated to be a live workhorse.

On all of the grid bias amps above, I installed a bias trimpot. Why not do this? They do tend to run quite hot. And hey, you may save the life of that very expensive power transformer:

http://www.mojotone.com/amp-parts/Transformers_1/Ampeg-B-15-Power-Single-Primary-Transformer

So if you have a serious recording studio, don't go without a real flip top. Even the B12SB amp is a fine choice for your bass tracks. I wouldn't buy a new one, there are so many good old ones around and they can be had for not too much. A late model can sell for less than a grand, middle period between $1.5k-$2k. Early ones can be a lot more but if you have the dough, a good tech or some good skills on the bench, you will not regret it.

JB

Yet another Fender Blues Junior!

Yup. These can possibly be the most popular tube amplifiers in the world at the moment. Really, as far as new tube amps that are factory mass produced, this series is the best bang for your buck. I wouldn't consider much else out there including Mesa, Marshall or Peavey. Why? By some miracle Fender stuck to Leo Fenders vision of having equipment that is easily serviceable. The other companies seem to have a hatred of service people, so I don't mess with them. I like making money see, not wasting time. In and out and get paid. With so many of these about I can afford to say no to a lot of new amps.

These and their ilk come through often. I just had a Hot Rod Deluxe yesterday. They always have the same problems. Solder joints crack and the input just falls apart. Yes, they use crap parts to keep the lights on. Who can blame them? Good thing is these are easily fixed and it's really easy to put a proper Switchcraft J12 jack in. It's so routine that I don't even keep the stock Fender jacks around. Those just suck so for $5 more I say keep your customers happy. Unless you are like our medical industry where it profits by keeping people sick. No, I have morals and a sense of decency.

Jack!:

These have 3 circuit boards. Pull them and re-solder every socket, pot, jack and ribbon connection. 90% of the time and you are ready to go for another 5 years.

When I was doing this a lot more I installed a lot of mods in these. Most were from this cat:

http://billmaudio.com/wp/

Good stuff. Worth the effort. I also installed carbon composition resistors and nicer caps in many over the years. Much to my surprise the effort was worth it. More 'vintage' sounding meaning just smoother and more musical. Rock bottom priced resistors and caps produce mediocre and rather harsh results. That being said stock these are just fine too.

This is a late 90's model. Still has the Eminence made speaker rather than the Jensen. This is a far nicer sounding speaker. I like these. Nothing special, just really good and full, not harsh like the Jensen tends to be.

Other improvements? Not really necessary but I have dropped in Hammond and Heyboer transformers before and the results were pleasing. Fuller body on both of those. More iron, better bass.

These amps are a positive holdover from what I call the EL84 revolution. Back in the 90's the shift went from big amps to smaller. The tube business was changing constantly with wild price fluctuations, a war in the former Yugoslavia eliminating the EI tube factory production and a growing demand for tube amps with a shrinking supply of good tubes. Sovtek made and still makes a decent EL84. We were bummed when EI stopped cause theirs was sonically superior. JJ took that chair, I like those just fine myself. Many boutique makers started building around the EL84 cause they were cheap and plentiful. It got to the point where I was bored of this tube. "Our amp is a sweet spot between a Vox, Fender Deluxe Reverb with a Marshall crunch blah blah....." Boring. Make something that doesn't try to please everyone please!

But I'm over that. today the EL84 is relatively cheap and plentiful still. Many clubs here in NYC have one of these little Blues Junior amps available for the back line and I'm always happy to see one. They kind of get out of the way of your expression which is what a good amp should do. I can always get my bag out of the speaker, clean or gritty.

I've never owned one myself but if I had to I would be just as happy. They kind of can't be beat! (Yo Fender, where's my endorsement??)

-J

Marshall Popular model 1930, circa early 70's

Here's an amp you don't see every day, a Marshall Popular 1930 model. It's a 10 watt 2x10" speaker amp. I've probably worked on 4 of these in the last 25 years, they are quite uncommon though not as rare as the really sought after and far more costly 18 watt 1974 model.

These apparently were only made for the European market so you'll need to either buy a step up transformer or replace the power transformer for domestic use. I know. Replacing a transformer is sacrilege. Whatever. Stick the original in a box and put it away until the day you sell the amp.

This came through with a problem all of them seem to have. Noise. Particularly buzz and lots of hiss. This particular amp was, um, 'converted' to an 18 watt model. A 6CA4 tube was added in place of the silicon diode rectifiers, the output tubes are the more desirable 6BQ5/EL84 tubes rather than ECL86 and another 12AX7 tube was added. Nice thing is all the socket holes are already there as these seem to share the same chassis as the 1974 model.

The intention of the job was good, the execution not so good. I did like the normal channel, it broke up immediately as a result of there actually being an extra gain stage.

So first thing to address was the hum. That was easy. change the filter caps and cathode caps. Hum gone. The challenging parts were: dead tremolo and buzzzzzzzzzzz hisssssssssssssssssss. Un-useable at low volumes. Turn it up and rock out and it's heavenly. You stop playing and you want to turn the amp off.

The tremolo usually dies from dead caps. You know, those 3 in a row typically ceramic caps. Tried that and no life. In this amp the cap going to ground on the tremolo stage was a .1 from the factory. I changed that to a .047 and started getting some oscillation. But not good enough. I noticed when the person modded this amp they changed the power supply resistors to higher values. My guess was they were as frustrated as I was about the buzz and this was an attempt to clean it up. I used the stock values and voom voom voom voom. Tremolo is roaring back to life. And....more buzz and hiss than before.

Yes, already tried new preamp tubes. Also changed load resistors, took out gain stage to see if the stock circuit was quiet. Nope. It all comes from the tremolo oscillator / gain stage. Pull that tube or alligator clip the signal to ground and it's quiet like a dead fish.

Also pulled all the pots and sanded the front of the chassis to tighten up the signal grounds. A minor improvement. Marshall used mechanical grounding in those days. Sometimes maybe in certain conditions, corrosion can happen and you get noise.

But that didn't solve the problem. Worked like a charm in other amps. Rats......

Time to resort to the forums. Type in Marshall Popular noise hiss.... Took me a while to find this problem addressed but I did find it. Someone post this question, a discussion followed that got heated and ugly as forums can do. (These amps are crap! No they aren't! Piss off! Moderators shut this down!). One person attributed the issue to hearsay about the phase inverter. Bollocks. But one person said this: "It's a flawed design. There is no gain stage between your guitar and the volume/tone controls thus causing excess noise." My first reaction was "WRONG!" Add gain, you add noise. This makes zero sense to me. And his comment generated no other comments. So being that it generated nothing and I was bored of this amp I figured he was on the right path.

So I tried it. Moved some wires around so it's more like the 18 watt (I've built a dozen of those, they are quiet!) and lo and behold, QUIET! Minimal hiss, no buzz, great sound.

Amp is loaded with the original Ceslestion 10" speakers. Always a bonus. I did wind up swapping out the power transformer just for ease of use. Plus, my client has a nice house with beautiful things. Having a step up is just kind of ugly. Which part did I use? The Mojo 18 watt power transformer. I did add a 100 ohm 25 watt dropping resistor between the rectifier and the first filter stage. This got it from the 350V to 325V range which is close to original.

So my take on these? Stock they really aren't that good. And the price people ask for these is stupid. Modded they are great. The complaints about them, noisy and thin sounding, are well founded. I, like most of us, prefer quiet and full sounding. They have the potential for that. But don't pay $2500-$3k for one. I'd sooner buy an 18 watt clone for what I want and spend the rest on a ticket to Italy. I would love to see more sanity in the vintage market. If these were great out of the box I'd happily pay what people ask. They are a cute little recording and club amp. When you've spent a lot then you buy into the anxiety of "will making it functional make me lose all my money????" To me something is only worth anything if it's useful. Fortunately my client likes things that work and sound awesome over just things to look at. What rocks stays, what sucks goes away. That's just sane. In the end, I really like this amp now. I wouldn't think twice about taking it on a gig. It really does give up a beautiful sound that is right between a Marshall and a good Vox. With my Fender guitars it's good and clear. Humbuckers it goes into full bodied overdrive without ever getting mushy.

-J

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!

-JB

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!

JB