1993 Vox AC30 Korg Reissue. Unbelievably terrible, simultaneously amazing. Hum and noise issues....

 

Here was a really tedious, un-fun job. Initially it was blowing one of the heater fuses. A mystery since my client said he changed the speakers to nice Blue Bells and it simply quit working. I was hoping for a quick fix and as it turned out it was a simple problem: one of the chassis nuts came loose upon re-assembly and it shorted out the heater.

But then I figured while I'm in here I'll recap the thing. It is 30 years old after all. I'm glad I did. The first two caps were leaking badly so I did them all. The client also wanted me to modify the tremolo and take that stupid 3 position "all of them are too fast" switch out and replace it with a 1 meg pot. Not an easy task, I needed to unsolder the little PC board that has the trem speed and type switches, carefully saw it in half, put the type switch back in and then hard wire a 1 meg pot into place.

Done. Re-assemble.... and...... damn. This thing sucks.. It's un-usable. So much hum, hiss, RF bollocks going on. I remembered hearing about these issues but other than re-tubing a handful in the past this was the first time I've ever really had to sit with one.

It was bad...... really bad.

I recently did some work in two OG AC30's for my man Sonic Dave in Vermont. I undid some sloppy tech work and tidied it up. There's no such thing as a quirk free AC30, they really aren't that good in a lot of ways other than the awesome sound they produce, but both were easy to deal with and had no objectionable hum.

I remember when these Korg reissues first came on the scene. They were touted as the first reliable AC30, which after the nightmare versions of the 70's and 80's, was objectionably true. They are great road dogs. I wouldn't consider taking a real one on the road, they're fragile.

What I find astonishing is how the good people at Korg simply chose to ignore decades of amp building wisdom and, excuse my language here but I'm pissed...... how did the fuck it up so badly?

The entire circuit board is a ground loop to begin with. It needs to be chopped up into 3 sections and that's just the beginning. I'll provide a path to a video from a fine tech for your viewing pleasure and I hope he doesn't mind. I will not show my own work here just like the tech in the video because if you can't understand exactly what he's talking about then you have no business doing this yourself. It's a big job and PC board amps are not like working on a good ol' tweed Champ. Cutting solder traces sounds easier than it looks.

I will give you this piece of information however:

Last night I tossed a coin to see if I should add a hum balance pot on top of everything else. It came up positive 2 outta 3 tosses which means hellyeah! 

I'm glad I did. When you turned all three channels down it hummed and buzzed. If you turn up the normal channel that goes away. So I turned them all down and adjusted the hum balance. It's as close to dead quiet as it can possibly be without changing the power transformer which has a mechanical hum. 

Anyway, search this on Youtube: 

AC30 Comparisons - TB/TBX Hum Fix

The tech says exactly what I say here: do not attempt this unless you have a lot of experience. He was annoyed too. He doesn't like to give away information for free understandably but I'm grateful he did.

So if you buy one of these, buy it CHEAP..... unless said work has been done. Or pay me $600-$900 to get it right. This was an 8 hour job. I like perfect but I'll stop here. Perfect would mean changing the power transformer as well.

How does it sound? Awesome......... No joke. It's an AC30. Now reliable and useable. 

JB

1978 Traynor YGM3 revisited. Well, that didn't work!

So my last post was about this lovely Traynor YGM-3 and specifically what to do about that high EL84 eating plate voltage.

The solution I tried was to use the Sovtek EL84M, rated for higher current and a whopping 500V on the plate. The amp left here sounding lovely.....

But, well, that didn't work. In this business one is always experimenting, largely to keep the cost reasonable. This is an expensive business. And I don't like seeing a customer return for a long time. It's not ideal for them especially.

And I'll just say it. I'm not here to sell anything, not even my services. So I can be honest here.

New tubes suck. It's just a fact we need to live with. The world will never produce another RCA, Mullard, Tung Sol, Western Electric, General Electric, Mazda, National Union, Amperex, Brimar or genuine Telefunken tube again. There is absolutely no incentive to do so. We need to live with the mediocre in this world now. Music is changing, the world is changing. There will be no exceptional tubes ever made again much like there may never be another platinum record again. It's over. Music is free, the population of guitar players and audiophiles is diminishing. I love tube amps. I find them fascinating so I carry on. And I will play music till the day I die and I will sound my best till then so that is that.

So what happened? My client got home and rocked it out for a couple rehearsals. It sounded great then it ceased to sound great. One tube totally died, the other test about 1/2 on my TV7 tester.

Not acceptable.

There are several ways to drop voltage. Zener diode, dropping resistor. But I don't like those methods. Since my client wants this to be road ready we opted for the most expensive route: changing the power transformer.

I used a nice Canadian made Hammond, part number 270DAX. I write this so I can have a record of it. If I see another amp I can just tell them their options if they want reliability.

With the original transformer the B+ sat around 425-440vdc. With this part depending on bias its between 329-345vdc. About the same range as your Blues Jr. Those run hot but they are reliable. I think this is a safe range.

You do lose a few watts. But the amp sounds as good as it did before, a tad warmer my ears say.

Nice thing about this part is it's the same size as the original. You need to get creative with some washers to run the heater wires around to the chassis hole, drilling is not an option here, and with that I had no need to drill anything. It's a 520 vCt transformer so you'll need to take out the 2 diodes going to ground and put the red/yellow CT wire to where the diodes terminated otherwise you'll have some seriously high voltage problems!

Once that's done you'll need to change the bias resistors until you get an acceptable range. In this case I changed the 18k coming off the AC feed to a 10k and replaced the 22k  with a 7.5k tied in series to my 20k trim pot. Now the amp is sitting at 329vdv with 22ma on the output tubes. That's about where a Blues Jr sits.

So in conclusion, if you have one of these this is a good path to reliability unless you have the dough for genuine 7189 tubes. It's worth doing. I still maintain this is a great amp. Now it's a great amp for modern times.

JB

1978 Traynor YGM3 Guitar Mate from our northern neighbors

Here's a bargain amp. A late 70's Traynor YGM-3 Guitar Mate!

These were built in Canada. I've worked on plenty of Traynor amps before and am quite fond of them. They are built to last and can be had for a cheapish price. Much like Jim Marshall who was motivated by building a cheaper amp than the Fender amps around London, Traynor did the same thing in 1963: let's build local, high quality affordable amps for the new music being made. All in the name of problem solving. All in the name of service. The best stuff is motivated by those 2 very important human things.

This amp is all hand wired just like a boutique amp. My client bought this on Craigslist for $400....

I believe this to be the Canadian response to the Fender Deluxe Reverb. It has a single 12" speaker, tremolo and reverb with a bright switch. The biggest differences are the lack of a power choke, no reverb driver transformer (cheaper to use a capacitor!) and a pair of 6BQ5/EL84 power tubes rather than the American 6V6. The result is it sounds like an English Deluxe Reverb, more chime and accented mids like a Vox.

Hand wired guts:

One of the nice things about working on these old Traynor amps is you don't even need to pull the chassis. You can remove the 4 bolts holding the top on and simply pull the hood off. Then you're ready to get to work! Though I can't help but think of brain surgery....

These amps boast the famous Mullard "Mustard" capacitors. Those are almost always still good so I'm leaving them alone. The amp hummed badly and sounded harsh. I knew right away what was up: bad filter caps and one dead power tube. Turns out one tube was completely dead, the other was very weak.

So a word about the tubes in these. They tend to get eaten alive. The new JJ or Sovtek / Electro Harmonix glass? You may experience shortened tube life. Those tubes are rated for around 300 volts. This amp boast around 420 volts! Luckily my client wanted more headroom so I just ordered some EL84M tubes from Sovtek. They are rated for 500v. They are the modern version of the 7189 tube. More for hi-fi like my old Fisher SA-100. Linear and clean. I find them to be very punchy, strong sounding tubes. They are a bit maligned by the guitar crowd, people prefer the sweeter tone of an EL84 but just keep in mind these are an option.

Cool Russian boxes!

 I re-capped it and added a bias pot. Due to the layout Traynor made the job so easy.... I used a 20K trim pot and changed the 22k bias resistor to a 15K cause the EL84M / 7189 biases a bit differently than a JJ EL84.

I also added a couple 1 ohm resistors from the cathodes (pin 3) of the EL84 tubes to ground. You'll read millivolts there which correspond to milliamps. 25mv=25ma. Easy and convenient:

I hate the bright switch in these. They use a .001 cap. It's like shaking a can of nails by your ear! I replaced that cap with a 100pf NOS silver mica cap. Now it adds a bit of smooth bite:

I ran it tonight with a set of JJ tubes running at 25ma each. I didn't get any red plate stuff but don't really trust them to last. The amp sounds great now. No hum at all unless you add that beautifully lush but humtastic reverb.

So if you want boutique quality at a crappy new amp price, don't turn your nose up to one of these. They can truly hold their own with the best of them. I actually like the rather mod styling too. Fender, Marshall and Ampeg went full industrial unattractive by this era. But these Traynor amps still have a touch of class. They look nice, and looks matter to me. If you buy one do keep in mind you'll want to get it checked out and possibly set it up with the beefier tubes. Unless you don't mind burning them up that is.

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

Trace Elliot Velocette. Oh, modern, amps. Why so lazy?

Had one of these on the ol' desk today, a Trace Elliott Velocette. I remember when these first hit the scene. The crazy 90's "there are no good cheap tubes except EL-84s being made so let's make little boutique sorta VOx sounding sorta Marshall sounding amps" era.

This amp came to me dead. No sound, no lights. Fuse was good, I had a hunch it was an internal fuse or the filament was dead. I haven't seen one of these in years but last one I worked on had a filament line issue.

 All tubes test good, high voltage is good. Yup, too much Bimoze on the filament line.

What's a Bimoze? I really don't know. I just like saying that.

So anyway, these amps are built in the typical modern fashion. With a crappy mother board where most of the components are attached. This includes your tube sockets as well. I never liked this. I'm not opposed to p.c. boards, but come on. Hand wire those tube sockets will ya? It's just better and more reliable. I know, I know. It cuts into profit. I'll shut up.

So the filament line comes off the power transformer into a connector that gets connected to the p.c. board that gets connected to another smaller connector that has wires going to 3 other connectors that connect to each tube. See something wrong with this sentence? It's a run on sentence and I say connector way too many times.


Photo of where the filament line connector meets another connector. Look at all that hot glue..... Got real handy with a razor today. Also notice the heat stains around the smaller black connector.

The underside:

This amp isn't very hard to get apart, that I appreciate. I just turned down working on an amp that I knew would be a nightmare. Life is too short.

More underside:

Hard to tell but wherever there is high current, there are cracked solder joints. This means filament line, high voltage line and speaker. Best to just touch up all of them while you are in there. Also touch up joints on jacks and pots. You can see what I'm talking about if you have a magnifying glass.

Connectors removed:

I wound up hard-wiring where the connector went to connector #2 on the first power tube. Lights on!

But..... after I put the amp back together, the other 6BQ5 tube wouldn't light up. Whack a Mole on such a simple amp! That connector was bad as well. In order to un-solder these connectors you need to remove the tube sockets. Um, EFF THAT!.

So I wound up removing all of these crappy connectors and hard wiring all of the sockets on the other side of the board. Now this little feller makes music. And sweet music it does make. These are really nice sounding amps. Almost has a 'gypsy jazz' quality to it. Warm and dry, cuts nice. They are cathode biased so you may pop in fresh tubes at will.

Speaking if which, one tube did start red-plating. They were just horribly mis-matched so I popped in one that was close. The only sets I have are JJs. Lovely sounding but I popped in 2 sets and they both started red-plating! I don't trust JJ EL-84 for class a operations. They are great for a Blues Jr properly biased but even in this amp, I don't like the risk.

Modern tubes.....bah.

I do like the styling of this amp. It looks like a cross between a vintage British racing car and a French bicycle.

Laziness #2:

Why write the serial number in pen?:

Can you read that? Oh well.

I would love to get one of these and gut it entirely then build a proper amp inside. But even stock, yeah, I would gig with this amp. It's strong point is that sweet, friendly voice it has. More my style then a Fender Pro Jr, which is a similar amp in some ways. I'm a huge fan of cathode bias. The sound produced is infectious.

JB