Vintage Vibes or Vintage Voodoo? Buying a Pre-owned Amp

New instruments, effects and amps have a lot going for themselves: They smell factory-fresh, they haven't been tampered with, and they are covered by a warranty. Nevertheless, many guitarists will – at some point or another – hanker for the pleasures only a vintage piece of gear can offer. The hard-to-pinpoint vintage vibes, the need to be one of the in-crowd, and the feeling that “they don't make 'em like they used to” do lure many players away from the relative safety of a music store, and into the untamed wild of the world of pre-owned and vintage guitar amps. This is a place where only the strongest will survive, and no prisoners will be taken. This article is aimed at reducing the risk of ending up with a piece of junk instead of a nicely worn-in amp. My examples will be taken from the world of Marshall amps, because they swing my boat, but you can use my advice and techniques also as general guidelines, when dealing with any older amplifier. 

General condition and test drives

When you've found something that whets your appetite, you should agree on a meeting and test the amp with your favourite guitar. When you see the amp in the flesh you can also assess its general physical condition: A tattered, battle-scarred amplifier should be considerably less expensive than a very clean (also called “mint”) example of the same model and vintage. The amp's cosmetic condition also tells you something about the kind of life it has lived so far, and how it has been treated. If an amp looks like it has been used as a snow plough, it probably was. But you always have to put things into perspective – if the amp in question was the well-loved workhorse of a single guitarist for 40 years, it will surely bear some battle-scars, which will tell a story and add to its vintage prestige. A much-gigged, well-used (but not abused) amp is not necessarily a bad thing, because you can deduct from its state that it must have sounded pretty good, at least to somebody's ears, or it wouldn't have been used that much.

If the amp is too far away to set up a face-to-face test, you should definitely ask the seller for as many different pictures of the amp – both from the outside, as well as inside the chassis – as possible.

What do I look for?

Look on the outside for a certain “coherence” in the amp's appearance: If you can see several different types of control knobs, non-original input/output/effects loop -jacks or differing types of metal retainers on the tubes, the amp has surely seen some modification. These changes are indicative of either servicing, the aftermath of an accident, or customization. With some of the older amps these changes may have also been down to an ignorant repairperson, who couldn't be bothered to use period-correct parts. If a component looks like it has been bought at the local home improvement store, it probably was.

When you fire the old amp up for the first time, you should turn your guitar's volume control off for a couple of minutes, and simply listen to the amp's own noise floor. This isn't an exercise in Zen, but rather one way of ascertaining the amp's condition. In a best-case scenario you will hear only a faint amount of 50/60-cycle hum with the amp's volume set to zero. Turning up the amplifier's volume should result only in adding “clean” hiss to the signal. If there's a loud low-frequency hum, irregular popping or clicking noises, or annoying high-frequency buzzing or squealing, you will know that something is not quite right with this amp. Again, use your basic common sense here and don't become paranoid, because there's always the possibility of a less than ideal mains feed in the building and/or household appliances (and lights) being responsible for the additional noises. Still, you should get to the bottom of any potential problem, before you decide to part with your money.

If at all possible try the amp out at gigging levels, too. This will throw up any potential problems much more clearly. Just ask yourself: Does this amp sound like it should? Is there ample punch? How well does it react to playing dynamics? Do you feel like angels have sprinkled you with magic fairy dust, when playing the amp? Or is the experience more akin to driving a broken Soviet tank through a half-frozen swamp?

Get the screwdrivers out

Either before – or after – the playing-test, it is very advisable to have a thorough look inside the chassis of a valve amp, especially with older (20+ years) equipment. So don't forget to take along a set of quality screwdrivers (at least Philips-head and flat), or, alternatively, a rechargeable screwdriver. This look at the amp's innards isn't meant to offend the seller: If the seller forbids you to open the amp chassis, simply gather your things together, say thank you, and leave the place without any further discussion.

DISCLAIMER: Danger! There are potentially lethal voltages present in any valve amplifier, which can lead to electrocution. Only ever open a tube amp's chassis, if you know how to handle the voltages correctly and safely (for example by “bleeding” the capacitors). The author and publisher of this article will not be held responsible for any injury incurred by readers handling a valve amp without the necessary precautions and technical knowledge!

Never, ever, open a guitar amp without disconnecting it from mains! Before doing anything else, you have to dissipate the lethal voltages correctly and thoroughly. The easiest way is to attach a crocodile clip to the amp's metal chassis, while connecting the cable's other end to the first preamp valve's pin number one. Then put the power and standby-switches to the “on” position, and wait for five minutes for the large capacitors to bleed their voltages. It is a very good idea to use a multimeter to make doubly sure that you won't get fried by touching the amp's components.

If this all sounds very confusing to you, and you're not perfectly sure of what you're doing, leave this job to a professional. Getting an electrical shock is potentially lethal, and really not a laughing matter at all!

Ooh, lots of nice little components!

Once the high voltages have been bled correctly, it's safe to have a closer look at the inner workings of the amp. If the seller tells you the amplifier is “all-original” or “mint condition”, its components should look coherent. This may sound a little hard to understand for a newbie, but it basically means that the same types of components should be “dressed in the same uniform”. 

The picture shows a Marshall Model 1987, built in 1975. The resistors are all of the same type – red-brown carbon composition resistors – while the capacitors are yellow, mustard-types. The two blue capacitors on the left are bias-capacitors, which are often of this type and colour in Marshalls. If these bias-capacitors are black and labelled Sprague Atom, there's no need to mistrust the seller. Electrolytic capacitors age with use and are some of the first components that must be replaced in old amps.

Also have a look for any signs of replaced burnt-out components, non-original pots (if one is different from the rest), differing cabling, additional holes in the chassis, insulation melted by a stray soldering iron, or any other anomaly, which might lessen the amp's resale value.

In this picture you can clearly see a repair in an early-Seventies Marshall: The pair of Icel polypropylene capacitors simply looks out of place, being the wrong size, type, colour and specifications, when compared to the original mustard-coloured capacitors on the left.  

Are amp repairs a sin?

Generally, there isn't anything wrong with well-made repairs and component changes. Many new components work at least as good as the old ones. If there has been a problem with the amp, it is good if the repair has been handled correctly. But when it comes to real vintage machines, where originality adds to their vintage value, people tend to take matters much more seriously. In the case of the pictured Marshall, a pious amp guru would have chosen period-correct replacements instead of the Icels.

Another, albeit less common, period-correct alternative would be using Philips' Mullard “chicklet-capacitors”. Problem is, though, that old, vintage parts are getting ever harder, and more expensive, to come by, making modern counterparts – like the polypropylene capacitors used here – look much more enticing. But then there's the vintage voodoo anoraks, who will point out to you that only a mustard-capacitor will “sound with a Marshall-character”, will be more “musical”, “muscular”, “leather-clad”, and more East End than Broker Belt. In terms of the practical value of an amp, well-executed repairs are a good thing, and if the amp sounds good with the new parts, then it sounds good – period. 

What can be counted as “vintage”?

Amps which are 25 years or younger, don't suffer from devaluation through modern components, in my opinion. If you go back, starting from the early Eighties, non-correct parts and repairs will have an impact on the amp's value, even if some purists claim that Marshall's golden age came to an end in 1973, when PCBs were introduced. The term “vintage” – originally lifted from the wine and champagne market – doesn't mean any old piece of junk, but rather pieces of equipment, which represent the pinnacle of a company's R & D and production output.

But newer amps, too, are starting to come into their own as desirable and collectible pieces of Rock 'n' Roll history, and prices have started to rise. A good example would be Marshall's Jubilee-series (made 1987-89), which got a lift from users such as Slash, John Frusciante and Joe Bonamassa. Still, generally speaking, the golden age of guitar amplification – Fender's, Gibson's, Vox', Hiwatt's and Marshall's classics – is generally placed before the advent of PCBs. 

This picture here shows a replaced power amp tube socket. You can still see clear traces of a valve burnout on the chassis wall, most probably down to a shorted-out valve, which had then taken down the socket and the soldered-on components right with it. The fuse must have blown in time, saving the amp from even worse damage. This is why any fuses inside the amp should always be replaced with the correctly-valued replacements, and not “bridged” with something as crazy as a nail. You can clearly see that the socket has been replaced with a different make. The chipped off red lacquer sealing on the fastening nut tells you that there has been a repair.

The grid resistor is also a newer model than the others used in this amp. It also looks like the technician has used two 100-ohm resistors to build an artificial middle output for the heater to cut down on hum. It might not be original, but it's a well-made and well-chosen improvement. You can also see some pre-drilled holes, which don't go through the metal all the way. Usually, those holes have been made at the factory. User-drilled holes tend to be drilled all the way through, and not always very clean.

Filter caps

Filter capacitors are used to filter any artifacts of AC-rectification from the DC-power used to run the amp. Some people insist on all-original filter caps, while others see them as aging components, which should be replaced well before they fail. Their normal lifespan lies somewhere between 10 and 20 years. The picture shows a pair of original Daly filter caps from 1975. If you look closely, you will notice that the caps have already started to bulge, which is not a good sign.

If you look for an amp to put in a museum, don't test drive this amp, just keep it locked away in its all-original state. If you look instead for an amp to fuel your paranormal waves of sheer musical inspiration, you will want to replace the filter caps before they fail. There are many makers of quality capacitors, one of them is German brand F+T.  

Transformers, or: Those ugly paper weights

When you talk to any exalted amp guru, chances are he will tell you that transformers are the soul of an amp, and that most of what we actually perceive as “tone” is down to an amp's power supply, made up of such stages as the power transformer, the audio transformer, the filter caps and the rectifier. This is why a genuine vintage amp should still have his original transformers intact.

Marshall has used transformers from three different manufacturers over the years – Radiospares, Drake and Dagnall. Radiospares-blocks are very rare and only found in the most-collectible of early Marshalls. Most other vintage Marshalls run on Drake or Dagnall transformers, identified on the transformer's chassis by a manufacturer's label and a model number. There are also combinations found in old Marshalls, like Dagnall transformers coupled with a Drake-made choke.

Marshall have never been sticklers for detail, when it came to selecting transformers – if something worked, then it worked. Since the mid-Nineties they have moved to using solely Dagnall transformers.

Here's a good listing of transformers and chokes Marshall have used over the years.

If you know which type of transformer to expect in a certain amp, it is fairly easy to see whether the amp is all-original or not. There is a problem with some old Dagnalls, though, because sometimes the type-number sticker can have fallen off along the way. In those cases, try to look for telltale signs of replacement, such as chipped off (or missing) lacquer sealant on the bolts holding the component in place (or on the soldered contacts). 

Heavy, heavy fuel

You will find mains power selector switches on many old amps, which is a good thing. Finnish mains power is nominally 230 VAC, which means the safest bet is to set the amp to 240 V. It isn't unusual to get a reading of 234 VAC off a mains socket in Helsinki. If you have selected 220 V as the value coming into the primary transformer coil, you run the risk of having too much power coming off the secondary coil's B+ and heater-outputs. This in turn would put an unnecessary strain on many of the amp's components over time, which would lead to component failures, sooner or later.

If your amp only offers you a 220 V setting – like most 80s Marshalls – you really should use a variable outboard transformer to take the voltage coming off the light grid down to a safe 220 volts. In most cases this will even result in better tone, because all the internal circuits will run at the voltages and currents they were designed for. My own Marshall 2555 sounds way sweeter when I supply its 220 V input with 218 volts instead of the 230 coming straight off the grid. 

Now put on your Stetson, and be on your way

Sure, there are a lot of mysterious variables when it comes to amplifiers, but you should approach each potential purchase with a positive attitude. Trying a guitar amp doesn't mean that you promise to buy it. Listen to your intuition, too. Get as much knowledge as you can, and try to approach each interesting amp with a rational mindset, instead of getting too excited by your find. But this isn't rocket science – a little preparation and knowledge goes a long way, when it comes to assessing a used guitar amp, lessening the risk of getting a bad deal.

Don't forget to use your ears: Regardless of whether you're dealing with a legendary amp model or an amp that has been used by a name player, if the amp doesn't sound right don't buy it. Unless it's meant purely as a museum piece in a collection.

Good luck!

08.10.2014 Antti Härmä (Translated by Martin Berka)
The author is a battle-proven backline technician, as well as a hardboiled, certified honkytonkwoman.