Dave’s Corner: Six Ways To Give An Old Amp New Life

Almost any guitarist who has owned the same tube amp for a long period of time will have segued through this: you loved the amp back when you first got it, it sounded great and was perfect for your needs, but lately it’s sounding a little dull, lackluster, or is generally lacking in detail and character. It’s not that it “isn’t working”—just that it sounds tired, lifeless, and doesn’t react under your fingers the way it once did. Often that feeling will send a player in search of an entirely new amp, with the old amp popping up in the used listings pronto. If you liked the amp once, though, and your playing needs haven’t changed drastically, chances are a little tune-up will give a little bounce to your old pal’s step, and save you the hassle of cycling through a new merry-go-round of amps trying to find another that works as well for you.

If you’re a diehard amp nut you might be hip to many of these tips already, but we all know guitarists—often perfectly good musicians, pros even—who will own an amp for years and years without giving a thought to its maintenance or general condition, then decide to sell when “it doesn’t sound so good,” rather than undertaking an easy fix. This blog isn’t intended as comprehensive trouble-shooting for outright failure, but these six maintenance-or-mod items are the most common ways to give new life to an amp that’s lost its sparkle.

1. Give It Some Fresh Tubes

This might be the most obvious and most common pepper-upper for tired amps, but too often players fail even to give this one a shot before consigning an amp to, well, the consignment sale. One of the first things I’d try with a formerly lively amp that was suddenly sounding dull would be to pop a good new preamp tube into the first position to see what that did for me (this tube is often called “V1” on diagrams, and is frequently the furthest socket from the larger output tubes). If I had, or could afford, a good, tested new old stock (NOS) preamp tube I’d favor that, but a good new make from a reputable dealer is just fine, and there’s plenty of variety in great-sounding new preamp tubes available today, too. Understand that preamp tubes don’t fail as frequently as output (a.k.a. power) tubes, and decent ones should last several years unless abused, but they will sometimes go dull prematurely—and they are cheaper than your bigger tubes, and easier to replace, so this is why I’d try this first. If you have more than one good, new or NOS preamp tube handy try them in other positions too, but V1 will usually elicit the most prominent sonic alteration or improvement.

Genalex Gold Lion KT88 Vacuum Power Tubes

Depending on how often and how loud you play, output tubes might need to be replaced anywhere from every six months to every two or three years (or longer if you’re a hobby player who doesn’t fire up the amp more than briefly once or twice a week). With some amps you can just buy a good quality matched set and pop ’em in—following your manufacturer’s instructions, of course, and reading up on other advise for tube replacement beforehand (at the risk of making a gratuitous plug, the newly published Updated And Expanded Edition of my book The Guitar Amp Handbook discusses a lot of stuff regarding tube replacement, as do other reputable amp books). With others, you will need to bias the output tubes when you replace them, and if you’re not trained in such work it’s a job for a qualified repairperson. It’s worth doing, though, and it shouldn’t cost a whole lot more than the price of the replacement tubes.

2. Replace Old Filter Capacitors

If your amp hasn’t had any general maintenance in 15 to 20 years, there’s a good chance that it needs new filter caps. If you know for certain that it hasn’t had its filter caps replaced in a good 20 to 25 years, or is a vintage amp that’s never been worked on, you can bet a cap job would do it some good. If the caps are that old or older and haven’t failed, you can opt to just keep playing it, and if you love the way it sounds then it’s hard to argue against that—except to say that caps of 20 or 25 years old or more are pretty likely to fail at any moment, and sometimes they cause bigger problems when they do, so a little preventative maintenance is often a good thing.

The filter caps (a.k.a. electrolytic capacitors) filter out noise-causing ripple from your amp’s power supply to help it operate as quietly as possible. In addition, they also play a big part in determining the tightness of the amp, and its low-end solidity. Old or failed filter caps will often result in a soft, flubby low end, and usually some dissonant odd-order “ghost note” harmonics, too. These symptoms go straight to the heart of a lifeless, farty tone, and a cap replacement in such cases often perks up your amp’s performance big time. Filter cap replacement involves working in parts of the amp where dangerously high voltages are present, so it’s definitely a job for a pro. That said, it’s usually one of the less expensive internal maintenance items, depending on what types of caps your amp needs, how many, and how tricky they are to access.

3. Ditch Leaky Signal Caps

.001uf 100v 5% GE Branded Coupling Capacitors

Signal caps are technically known as “coupling capacitors,” because they couple together different signal-carrying stages within your amp. They are similar (and sometimes identical) to the tone caps attached to your guitars’ tone controls, and are sometimes called by that name too. Worn out coupling caps can become “leaky,” which means they don’t block the voltages they are design to block, and don’t let their particular circuit stages perform as they should. Other than in particularly old vintage amps that were originally made with failure-prone signal caps, the several signal caps within any amp don’t generally go bad all at once. You can bet, however, that any amp from the ’50s or ’60s will have at least a few leaky signal caps, and even nearly-new amps might display a failure here and there in this department, if a part unexpectedly experiences the occasional early demise that can strike even the best components now and then.

While this is another job for a pro, you might want to have some input—and insist on some consultation mid-job—if you’re surrendering a particularly valuable vintage amp to this kind of work. In the old days, repair guys would often just rip out all of your tasty old vintage signal caps because it was quicker and cheaper than properly diagnosing which were actually at fault. A tech who is familiar with vintage amp values will understand that you want to preserve as many original components as possible, as these can play a big part in any old amp’s sonic character, as well as its value, but it doesn’t hurt to remind them to go easy. With newer amps, ensure replacement caps are at least as good or better than what was originally in there—or read up on some upgraded replacements and see if they do anything for your tone.

4. Swap That Speaker

Avatar Hellatone 25w Speaker

In many cases a speaker swap is the fastest way to elicit a fresh new sound from an old amp, or to completely re-voice an amp that is working fine, but which needs a tweak to hit the zone you’re chasing. Often times it’s one of the cheapest, too: many good replacement speakers can cost well under $100 (although you can spend two or nearly three times that much if you want to). Also, you can usually do the job yourself, if you’re careful and read up on the procedure. Some amps benefit from a new speaker because the old one just wasn’t a great component in the first place, or didn’t maximize the potential of the amp; others might be tweaked to achieve slightly different tones that are supported by a carefully selected replacement speaker more than they are by the one that’s in it now. Also, while the original speakers in many vintage amps usually constitute and important part of their value, and often their original sonic character too, older units are often softer, duller, and less efficient than good modern replacements (though not always, by any means). I’ve encountered countless players over the years who raved about how an old amp came to life when they finally swapped out the supposedly “great” original speaker. On top of that, putting a new one in there helps to preserve the old one for a time when you might want to sell an amp in original condition.

For more on the subject of speaker swaps in general read up on the characteristics of different replacements out there today—it’s a booming market—and check my Speakers For Tone Tweakers Reverb blog from this past February.

5. Clean The Connections

Any amp part with pins or contacts that transfer a signal from something else that’s “plugged into it” can become dirty or tarnished, and therefore fail to transfer signal with the utmost efficiency. This goes for input jacks, speaker output jacks, any effects-loop sends and returns, and all of the tube sockets. A simple cleaning of these parts with a good contact cleaner (DeoxIT, No Flash, or similar) can often work wonders to get your full signal flowing again, and help your amp sound clearer and sharper in the process. If you have to open up an amp’s chassis to get at these things—and you usually do—you should have a pro do this work for you. While he or she is in there, also have them clean all the pots and, if necessary, tighten the tube socket’s pins, too. Short of taking it to a tech, you can go a little ways towards cleaning input and output jacks by spraying contact cleaner on a cotton bud (a.k.a. Q-Tip) and working it back and forth through the hole until you come away with some indicative grime on the bud’s tip (yeah, sorry, I know, but don’t know how else to describe this procedure). Also, you might get away with spraying just a quick squirt of approved cleaner into your tube socket’s pin holes, or even onto the tubes’ pins themselves, then inserting and removing the tubes a couple of times.

6. Get Your Amp “Voltage Correct”

AmpRX BrownBox Input Voltage Attenuator

This one might be a little more esoteric for some players, and for some techs too, although the good ones will quickly figure out what I’m talking about. Vintage amps from the ’50s, ’60s and even early ’70s were often designed to run on domestic power outlets delivering anywhere from 110V to 115V AC, but usually don’t function as they should when hit with a lot more. They might work, sure, but their components will be under greater strain, and they often won’t sound they way they were designed to sound. Combine these facts with the reality that many of our wall outlets deliver anywhere from 120V to 125V AC these days (and will vary at different times of day, too) and you’ve got a potential situation. Even newer amps that were designed to run on around 117V to 120V might have undergone wear and tear, or drifted off spec in ways that render their internal components seeing more voltage than they’d like.

To rectify all of the above (no pun intended), have a tech check the operating voltages at various stages within your amp against the voltages indicated on an original service schematic or diagram, and to do whatever’s possible to bring things back into spec. Such a service should also include a re-biasing of output tubes when the work is done, or perhaps a check and replacement of the large bias resistor in cathode-biased amps, if that’s deemed necessary to bring your amp in line with desired specs. The voltages in some amps can be brought down to spec with the use of a different rectifier tube (if the amp has a tube rectifier in the first place), or some other internal fixes can be undertaken. Or, you can acquire an external voltage-reduction device intended for this purpose, such as the P3 Line Tamer or Amprx Brown Box, and regulate your amp’s input AC voltage in this way.


ABOUT THE AUTHOR: Dave Hunter is a writer and musician who has worked extensively in the USA and the UK. He is the author of The Guitar Amp Handbook, Guitar Effects Pedals, Guitar Amps & Effects For Dummies, The Gibson Les Paul and several other books. Dave is also a regular contributor to Guitar Player and Vintage Guitar magazines. The Updated And Expanded Edition of Dave Hunter’s The Guitar Amp Handbok: Understanding Tube Amplifiers And Getting Great Sounds is now available from Backbeat Books. See some of Dave's books on Reverb here.

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