Shit Happens, Don't It?

Folks, just a message from your friendly local neighborhood amp mechanic.

You're doing yourself a disservice if you're looking for a cheapish amp and you buy something for which the manufacturer will not provide support information to the trade.

It may be an orphan you bought on the cheap and you're not out much, but it may be something that looks good on the showroom floor but which the manufacturer does not, or more often, will not support out in the field.

 When it breaks-and what amp doesn't over the course of its life?-if your technician can't access the necessary road map-errrrrrrrr, schematic and list of components-you're faced with a choice of either tossing it in the trash, selling it for salvage parts, or sending it back to the manufacturer and taking what they are ready to give you and liking it.




Yes, I know it may be under warranty, but you've still got the logistics problem and we all don't live in New York, Los Angeles, Dallas, or Atlanta.

If it's not under warranty-a craigslist or ebay buy-and you can't service it locally it is just an expensive and useless piece of luggage.

Of course this rules out Blackstar, Bugera, Line 6 and probably a whole bunch of others. It rules in Fender, Peavey, and Traynor, all of whom are known for product support.

You owe it to yourself to find this out before you spend your hard earned dollars and not after the money's gone.

Retrofitting an Ultralinear Twin Reverb

This formerly ultralinear Twin Reverb belongs to a local fellow who acquired it in a curious way. Seems he's a journeyman steamfitter and he was working at a school in Bode, Iowa a number of years ago. He heard casters being rolled across a cement floor and poked his head out of his work just in time to stop the amp from going into a dumpster.

It seems the scientists at the school decided it had a bad power transformer, removed it, and then decided as it was too expensive to buy one that they'd dump the amp in the trash. So he got it sans power transformer and it sat for a few years until the work picked up and he could afford to get it repaired.

The ultralinear Twin Reverb was an uprated amp capable of producing a rated 135w, and they did it by using an ultralinear output transformer. This uses screen taps at about 70 per cent and the idea is that you can run the plates really hard and still keep the tubes alive. It yields clean, glassy tone that seems a bit sterile. But did I say they're loud?

And thereby hangs a tale. Power transformers for these things are a little unusual because the rectifier setup is different than the older Twin Reverb amps. It delivers more voltage because it is a full wave bridge, with a non center tapped secondary.

According to the good folks at Hammond the previous way of doing things yielded an average DC voltage of about .45 of the AC voltage and the ultralinear amp setup yielded more like .90 of AC voltage. So you can't just drop any old transformer in and hope to have a working combination.

The quest began, and the price for a replacement Mercury Magnetics power transformer was nearly three hundred dollars. Ouch!

I did locate a used one but the fellow first wanted a new Classic Tone (Magnetic Components) Twin Reverb international voltage power transformer and a new Classic Tone output transformer to go along with it in exchange for a used, single ultralinear power transformer.

I thought it was too much, highway robbery really,  and he dropped the demand for the output transformer-no doubt figuring he could use the one he had.

I still don't like the idea of being hosed for parts by strangers so I nixed the deal entirely and decided to find something else more suitable, as I'd seen used ultralinear power transformers on ebay  for around forty to fifty bucks.

Had he merely said at the beginning "I want $120 for my transformer" I would, in all likelihood, have gone for it. But that's the rule of life-ask for too much, try to take advantage of people and you're more than likely to get nothing for your trouble but some unhappy folks.

I then obtained a standard Twin Reverb power transformer used for a Grant and a new choke from Mojo and built a bias-rectifier eyelet board, redid the power supply capacitors and the necessary rewiring, converted the bias to a level set and revised the phase inverter circuit to standard and then......nothing. No output to speak of.

Measuring and reevaluating my voltages I came to suspect the ultralinear output transformer was the source of the original malfunction all along. I had a new Magnetic Components transformer  in house for another project and installed it.

Some minor tweaks to the wiring, relocating the bias control to a safe place, and other minor touches

Volume, lots of volume. Tons of tone and plate voltages right at a steady 450v DC.

Useful Things From the Past

Every once in a while you come across something that's such a good idea that you replicate it.

The item below was a promotional pencil handed out by the Gifford-Brown folks when they were still in the electronic components trade.
What it is, of course, is a tube tapper, although the rubber erasers had long since dried up and gotten as hard as granite. It's good for testing tubes for unwanted noise when installed and running. I guess in a way it proves that the problems in the service trade are not all new.

So I put together my own out of a couple of pieces of hardwood dowel that accept rubber cap erasers of the kind people put on pencils-although even pencils are fast becoming obsolete items that tend to confuse the young folks.

A pencil does not come loaded with high definition content and it will not log you onto facebook or get you in touch with your BFF. It will also not let you send a picture of your tackle to your girlfriend and then have to tell her parents and yours and an army of policemen that it was all in fun.

You're welcome to make your own tube knocker and I commend it to you.

On the subject of pencils, I kinda like them.

When I was a little kid in Miss LaPolla's first grade class I'd always get stuck with the pencil that had a busted up inner lead, and frequent trips to the Boston pencil sharpener were an embarassment.

There and then, I swore a dark and bloody oath-which is a funny thing for kids to do-that when I grew up I would have as many pencils as I wanted, and as many pencil sharpeners as I wanted so that I could have as many well sharpened writing instruments as I pleased.

Well. Here it is, fifty seven years later, and although many opportunities have escaped my grasp since then, this one can be checked off my so called bucket list. I have a lifetime supply of good pencils, cap erasers for the ones that are dried up, and a fine selection of Panasonic electric pencil sharpeners for every mood.

Every now and then I'll sharpen up an older cedar pencil, and the smell is enough to take me back to that classroom.

I showed 'em.

Transformer Design Math Simplified: News You Can Use

Here's something I tumbled over in my latest search for interesting things to do. Building a transformer or rewinding one seems like a worthwhile project and it'll more or less compel me to finish building my hipot tester. Credit for the fine folks at Radio magazine, who put this out in 1922. Public domain, y'all.

The old man always said I was working on my doctorate in obsolete technology. He was right-I'm a throwback.

Enjoy responsibly, as they say in the ads for people antifreeze.

Resuscitating a Peavey Valveking 212

This Valve King 212 arrived here completely defunct with a blown power tube.





This amp is one of a series of amps that Peavey, formerly doing its assembly in the US, farmed out to the Chinese. As these things go it is only a shadow of the old Peavey amps that were made in the seventies and eighties in Meridian. The cabinet's MDF fiberboard, and the amp itself is lightly built with spindly circuit boards.

It's got a major design flaw and thereby hangs a tale. The tube filament supply and the low voltage supply for the solid state devices and channel switching relays is part and parcel of the same circuit. When (not if) there are problems in the power tube end of things it's likely to affect everything else in that part of the neighborhood because they're plumbed directly into this one circuit.

And, the fuses are pigtail types soldered to the circuit board.

It's a shitty way of doing things for reasons that are now to be revealed.

When one of the power tubes in this amp erupted, before the fuse had a chance to react (I'm theorizing a bit here) the voltage and current surge took out the filament diode bridge and a bunch of other things downstream including several other diodes, a transistor, a pair of JFET switches and the main relay itself. When the amp is powered up this relay is energized and stays that way. Until it gets toasted.

So the first adventure was to restore the filament and mains voltage and get a set of functioning tubes installed-which I did, which is when I found out that the channel switching was defunct. Several hours of troubleshooting various components led me to use a bench power supply to put 12v on the relays which is how I found the bad one.

Then it was off to spending a couple hours finding a data sheet for the existing off brand relay, and then finding something that did the same thing-that's two hours of my life I'll never get back. At the same time I ordered Q101, 102 and 103, as well as a socket and a dual op amp for the reverb side.

When all these things-diodes, transistors, switches and relay were installed, then and only then could I discover that the reverb was inoperative.

After further testing this morning I discovered that D118 had been fried in the general uproar. Replacing that got the whole rig operational, bias looks good, and I hope to hell the effects switching is OK because that's plumbed into it as well with a dual transistor I don't have at the moment.

When it was all assembled, it sounded like what it is-a three hundred dollar Chinese amp, thin, nasally and uninspiring.

Best bet? Save your amp money for something more inspirational.

When Giants Walked The Earth: The Mother Amp

We learned with sadness yesterday of the death of Jim Marshall, founder of the empire that bore his name. He was one of the last of what you might call the Founding Fathers of rock music.

What's of more than passing interest is the connection between the earliest Marshall amplifier-the JTM45-and the Fender 5F6A Bassman that it was reverse engineered from.

It seems that the manager of Jim's music shop had one, and at the time Marshall made the decision to start building amps, and as it was known his amp was outstanding, it was used as the model for the JTM45.

That amp was the Mother Amp. There was nothing like it, and it marks a tectonic shift in the progress of guitar and bass amplification. That was the start for Marshall which went on to bigger things.

I knew a fellow named Skip Grebis in high school where I grew up in New Jersey. One day he called me and said "I have the best guitar amp in the world here at my house. You should see it." I headed over and he had a 5F6A Bassman he'd borrowed from a cousin named Joe Rizko. I looked at it and smirked "It looks like a suitcase. Are you kidding?" He said "In a future time people will pay huge amounts of money for these things."

As usual, he was right although he didn't know and couldn't explain where he got his insights from. He's studiously maintained a low profile in Florida somewhere.

That's the problem with people who can see the future-the rest of us can't.

Making Your Mark: Reviving A Custom Vibrolux Reverb

Every once in a while you come across something that really, as they used to say in the Pepsi radio jingles, hits the spot.

Such are the Mark Moyer mods for the Custom Vibrolux Reverb.

With that said, a Fender Custom Vibrolux Reverb arived here with a really high level of background noise. Incidentally it had a scorched tube socket and failing electrolytics which didn't help anything.

In " The Soul of Tone" Tom Wheeler describes this as a production of Fender's Custom Amp Shop which was designed by Bruce Zinky. As a commercial item it was more or less a flop, because most people didn't like the noise level-you don't see them around much, and when you do, they aren't that expensive to acquire.

Back a decade or so ago, a fellow named Mark Moyer decided to tackle the hiss and noise problem with this amp and he developed a plateful of mods that move the CVR from an also ran to a great piece of gear.

The mods consist of delinking the reverb from the normal channel, installing a negative feedback loop, adding a shunting capacitor to the phase inverter, removing the surge protection diodes, and replacing the ground reference resistors. In addition and highly recommended is installing an adjustable bias control and replacing the 12AT7 reverb recovery tube with a 12AX7.

Don't forget to check the electrolytics for ESR-the power supply capacitors were failing on this amp.

The modifications will take you about an hour of work, after you've opened up the chassis, marked and removed the connecting wires from the board that have spade connectors, and removing the daughter boards from the front of the amp. If you're not handy with a soldering iron leave this to a professional.

You can find the rundown on these mods here.

If you're like me you'll find the transformation outstanding.