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 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