What you should know about buying a tube amp

I am often asked for some opinions about what people should buy in the tube amp world.

Here are my thoughts.

First, the basic platform must be roadable-that is, rugged and durable, able to survive temperature extremes, odd voltages in dodgy ginmills, and one that can withstand being bounced around in the trunk of a car for hours.

Second, the amp must-MUST!-be free of unnecessarily complicated circuitry and gimmicks, because those doodads exponentially increase the likelihood of maintenance issues, breakdowns, and, for the technician, countless hours spent in chasing down intermittent faults. Some of the design features overwork the key components, which are the tubes.

For the most part this rules out Mesa Boogie amps and similar analogues such as Bugera, B52 and many others. They are complicated to work on, service information is closely held and not available to the trade, and that limits the number of people who can or will work on them. I have always thought that vertical information silos depend on key people to be available when you need them. On the other side, broad based systems of general knowledge do not depend on key people and are thus more likely to be available when you need them. I recently had a Dual Rectifier Road King II in the shop with failing muting jfets of which there are 15 or so. By my count it had 33 knobs and 22 relays.

This increases potential failure points in a geometric fashion. If the failure point is A, you have one potential failure point, but if you have five potential failure points you have AxBxCxDxE potential for failure of a critical component. The quality of the components used can only compensate to a certain degree.

This is directly connected to Bayes' Theorem, which applies to probabilities. You can read more about it here.

My math may be a little bit lacking but I think you can see that complication leads to failure at inopportune times.

This is not to say that Boogies are bad, or evil. They are fine in the studio if that's what you like to do.

This in general rules out all amps that have more than two channels and use channel switching via relays, optical couplers like Vactrols, and the like. They're troublesome.

What you can do here, when considering an amp for acquisition, is go to the best most respected amp tech you know and buy them a coffee. Ask them if whatever you're considering is a good buy from the standpoint of serviceability and roadability. You may be surprised at what you learn in a face to face encounter with a real person.

Third-printed circuits. Are they inherently evil? The answer is no, if they're properly built with good components and proper engineering. They're a fact of life in this day and age, but they do require that the technician who works on them have a deft touch. They're less user serviceable than amps of an earlier era. They're also less damage and shock tolerant than traditional methods of hand wiring. Also, when troubleshooting down to board level faults, you may find the amplifier becomes uneconomic to repair.

Printed circuits have been around for a while now. The earliest one I have actually seen was in a Motorola table radio and it had a copyright date of 1956. At that time my father was working on a wave soldering project for Weston, so we've had them for at least sixty years. I'm informed that the first printed circuit boards with plated through holes was made in 1947.

Now, having said that, it is worth asking whether power tube and rectifier tube sockets are mounted directly to the circuit board. They generate heat-lots of heat, and the boards cannot withstand that forever. What happens is that the substrate gets carbonized to some extent, and as we all know carbon is what resistors are made from. That means that you start getting stray voltages and current leakage here and there. Ask the Marshall folks about conductive circuit boards in their DSL amps.

Also, circuit boards for guitar and bass amps are not generally available in the aftermarket, with very few exceptions. That means if the worst happens and a board needs replacement you may be out of luck. Occasionally some boards may be available in the secondary market or from friends in the trade but it is not something that can be relied on.

What this means is that you should spend all the money you are capable of getting your hands on and buying a hand wired amp built the old, artisan way.

Educate yourself on the methods by which your chosen piece of gear is built. Not all hand wired amplifiers are created equal. Learn about maintainability if you intend to take it on the road. Learn about after sale service and what you can expect from the builder.

Does that mean you should buy from a homebuilder who will assemble a kit for you? Probably not, unless you have seen examples of their work in the wild, and if the critics are satisfied.

All of this takes you back to the beginning. By far the best values for the money in the amp world are silverface Fender amps, some of the older Traynors, and some boutique-y amps such as Tungsten, Victoria, and Kendrick.

They're hand wired on eyelet boards and not overly complicated. With ordinary care they will last a lifetime of playing.

And last, do you like the way they sound? Do they speak to your style of music? Ultimately that should be the deciding factor.

The Cowpoke Forty, or, How I Stopped Worrying And Learned To Make My Own Bassman

You know sometimes how you get an idea and you just can't shake it? Gotta scratch that itch?

That's what happened here. The first Bassman 50 just didn't have any muscle, so I decided if I couldn't have a real Fender Bassman I'd have to build one myself.

The first step was to acquire a chassis and I was lucky enough to find a new production chassis on fleabay, the why pay more store. I already had, in no particular order, a Super Reverb power transformer from Pacific-nice stuff!-a Marvel choke, and a Classic Tone output transformer.

In short order I cooked up a circuit board from the usual stuff, punched out an extra hole for a rectifier tube, and commenced.

After some off and on work the Cowpoke as I called it was finished but still needed some fine tuning in the bass channel. Other than a tube rectifier it's pretty much all AB165 Bassman, and it was wired with traditional cloth covered pushback wiring, Omron octal sockets, and a mix of yellow poly and brown chiclet capacitors from China Inc-they were cheap at about ten cents apiece and do the job just fine, thank you.

For glassware it has a Raytheon 5V4, a pair of vintage Sylvania STR387s, a JJ ECC81 and a trio of JJ ECC83s. After trying it out I had to rectify a couple of mistakes I'd made with the wrong value caps in the bass channel.

That was all finished up today, the Bassman face plates were installed and in it went to make nice with the Weber Silver Bell that's in the J.D. Newell cabinet that I acquired a while ago.

You do not have to keep a Bassman power transformer in stock if you will but keep a Super Reverb/Pro Reverb power transformer. Just cap off the rectifier tube 5v winding if you don't like it. Stock one instead of two.

It's a good piece of kit and I will be experimenting with it and getting familiar with its Bassman goodness in the next two weeks or so.

The pictures.