Repair Guitar Amps

Dr.Tube is the specialist in the repair of (tube) guitar amps and other interesting music related analog (non tube) electronic audio equip­ment. Contrary to the vast majority of other repair shops, who find it is sufficient to repair to the level of “it works again”, Dr.Tube goes the extra mile to make an amp not only “work again” but also to make it really sound good again. A subtle but huge difference!

Dr.Tube has more than 30 years of experience re­pairing, amongst others, the following brands of guitar amps:
Aguilar, Alembic, Ampeg, Ashdown, Bad Cat, Bedrock, Blackheart, Blackstar, Bogner, Bradley, Brunetti, Budda, Bugera, Carlsbro, Carlton, Carvin, Castle, Concord, Conquest, Crate, Custom Audio, Dean Markley, Diezel, Divided By 13, DV Mark, Dynacord, EBS, Eden, Egmond, Egnater, Eko, Elk, Engl, Epiphone, Fane, Farfisa, Faylon, FBT, Fender, Floyd, Framus, Fryette, Gallien Krueger, Geloso, GEM, Gibson, Guyatone, GuyTron, Hartke, Hayden, HiWatt, Hohner, Holland, Hook, Hughes & Kettner, Ibanez, Jackson, Jet City, Kinder, Kitty Hawk, Klemt Echolette, Koch, Kool, Kustom, Laney, Legend, London City, Marshall, MatAmp, Matchless, Mesa Boogie, Morgan, Music Man, Orange, Palmer, PCL, Pearl, Peavey, Peterson, Power City, Randall, Red Bear, Rivera, Roland, Roost, Royal, Schaller, Selmer, Simms Watts, Soldano, Sound City, Sovtek, Stramp, Sunn, Super City, Supro, SWR, THD, Trace Elliot, Traynor, Two Rock, The Valve, Univox, VHT, Vox, Warwick, Watkins / WEM, Yamaha, Zzz…

Common guitar amp repairs at Dr.Tube are:

Retube

Retubing is replacing the tubes. Tubes are subject to wear and tear and have a limited lifetime. A guitar amp with old and worn tubes can:

• hummmmm,
• sound thin and lifeles,
• have difficulty “cutting through the mix”.
• hisssss and/or make crackling noises (fried egg noises),
• have ugly and unwanted distortion,
• have less power.

The wearing out of the tubes is a gradual process which means that you easily get used to the lesser sound.

Recap

Recapping is replacing the electrolytic caps (electro­lytics). Due to the way electrolytis are constructed and the high temperatures present in tube amps, electrolytics also have a limited lifetime. A guitar amp with worn and dried up electrolytics can:

• hummmmm,
• have less gain,
• sound dull and thin,
• can be troubled by ghost notes,
• have difficulty “cutting through the mix”.

Our experience is that electrolytics have a max­imum life time expectancy of around 10 to 15 years. So with a lot of older amps it is high time to replace these electrolytics, even if they look OK. There are modern electrolytics which really should be replaced the second the amp leaves the factory. Brands like Illinois Cap (we call these illinoise crap), Samwha, Teapo (cheapo), etc, come to mind. When we recap, we do not replace all the capacitors, just the electrolytics, as film (plastic), ceramic and mica caps usually can last many tens of years. If, however, one or more of the other caps are not OK, we replace these too of course.

The effect of fresh electro­lytics can be very pro­nounced. A lot of people do not realize/know this. We have often heard from many customers they should have had this done years ago.

Dr.Tube is very well stocked in high quality electrolytics for use in tube amps.

Bias Mod

When the power tubes are replaced the bias current (almost always) needs to be set correctly again. This is called biassing. Correct biassing is very important for good tone and a reasonable lifetime expec­tancy of the power tubes. In cathode biassed amps, like the VOX AC30 etc., this isn’t necessary or possible. In (almost) all Mesa Boogie, most Peavey and a lot of older Fender amps there is no bias pot where there should be one. The bias mod is installing a bias potmeter (so that the bias current can be adjusted) and one or more bias measurement resistors so that the bias current can actually be measured.

Major Overhaul

A classic old Fender, Marshall, Vox, London City (etc.) amp is often more than 30, 40 to 50 years old. Just like an old car such an amp seriously needs a major overhaul. Usually this is a combination of a retube, recap and other mainte­nance work. After such an overhaul the amp will sound like it did 30, 40 or 50 years ago when it came out of the factory. Dr.Tube uses new but “old style” components for repairs and maintenance so that these amps can be fixed historically and tone correct. In some cases these parts are specially made for Dr.Tube.

These kind of overhauls are often hard work but very rewarding to do!

JCM2000 Stable Bias Mod

The early Marshall JCM2000 amps often are troubled by a not stable bias current (drifting bias). On the JCM2000 Stable Bias Mod page it is explained what the root cause is of this problem and, more importantly, what can be done to remedy this problem.