How To Repair Tube Amps

Warning! High Voltage!

Guitar amplifiers operate on high voltages, the exposure to which can cause serious and fatal injuries. Never attempt any internal maintenance or adjustments yourself unless you are a qualified professional repair-person who fully understands condom practices in working with these components. Be aware that just turning off and unplugging your amp is non plenty to guarantee safe access to its internal workings.

The nature of many of a tube amps' internal components means that extremely high voltages are withal present fifty-fifty when the amp has been turned off and unplugged for a considerable period of time, even several days. Unless yous are trained and qualified to do so, never remove your amp'south chassis (the metallic box with tubes and transformers hanging exterior, and all the circuitry independent inside) from the cabinet. Leave such piece of work to a professional.

If you don't take much feel with basic user maintenance of the things, tube amps tin be enigmatic boxes full of glowing, hissing trouble. In that location are a lot of simple preventative and budget measures that almost players can perform for themselves, though, while several other bigger jobs should definitely be left to a pro.

Permit'due south take a look at several jobs y'all can probable undertake yourself with the right guidance and instruction, with a nod to those that you can't highlighted in assuming italics. We'll follow this with a list of repairs and maintenance procedures that are definitely best left to a trained technician.

The Practice-It-Yourselfers

Bones User Checks and "Rattle Diagnostics"

Every amp that'south used regularly, or certainly one that hasn't been used for a long while, should be periodically checked, tightened, and adjusted in several modest but worthwhile ways. Also, I accept often been surprised to find that an odd noise coming from the amp that I initially supposed to be electrical was actually a mechanical rattle, buzz, or vibration, which was disguising itself past blending in with the sound of the amplified guitar coming from the speaker.

Become your tool kit handy and attend to these matters, and you'll likely eliminate them earlier they have a chance to drive you crazy. Note that you lot might have to remove the amp'due south back panels to reach some of these, merely you shouldn't have to access annihilation inside the chassis (see our warning above).

Check, and where necessary tighten, these pieces of hardware:

The chassis of a 1955 Fender Tweed Deluxe

Handle or handle mountings.
Speaker mounting bolts, but be sure not to over-tighten them (see Speaker Replacement below).
Bolts or screws mounting the speaker baffle to the cabinet (see Speaker Replacement, below, for more info on the baffle).
Speaker cable, and specially whatsoever slide-on connectors that connect the cable to the speaker'due south + and – terminals. If these are loose, they might need to be gently crimped in with a pliers to brand them tighter.
Chassis mounting bolts and/or basics, which concur the chassis to the chiffonier. Don't brand them too tight, because locking the chassis down to the cabinet too tightly might induce mechanical microphony in some amps and tubes, only the chassis should be tight plenty that is doesn't wobble or motility at all upwardly-and-downwards or side-to-side if you wiggle it.
External bolts and machine screws that hold the transformers to the chassis, which can sometimes loosen over fourth dimension do to vibration.

Tube Replacement

Yous will likely exist capable of replacing many tubes, and preamp tubes in particular, provided they can be hands accessed without having to remove the amp'southward chassis from the cabinet (run into Warning!) and they are readily accessible. Before replacing whatever tubes, read your manufacturer's owner's transmission and any guide to adequate tube types to make sure yous're replacing like with similar—and aren't doing anything that goes confronting the manufacturer's recommendations or which might invalidate your warranty.

Tubes in a Tribute Amplification 8" 8E1

Exist sure to switch off your amp, unplug it from the wall, and let the tubes cool down for several minutes before touching whatsoever of them. (My previous feature "How to Amend Your Amp'southward Tone With Preamp Tube Swaps" has a lot more information on preamp tube replacement, besides as a department on how to remove and supervene upon preamp tubes.)

Preamp tubes practise not need to be biased, and are simply a straightforward like-for-like replacements, in nigh cases.

Some amps accept output tubes (aka ability tubes) that can exist replaced without re-biasing the amp, and your owner's manual should inform you lot of this. Others do require re-biasing, and unless you're experienced at doing this and accept the correct tools for the job, the procedure is definitely a job for a pro .

Rectifier tubes don't require whatever re-biasing or adjustment when they are replaced. But follow the safety and correct tube replacement procedures, and exist sure to replace the existing rectifier tube with one of the aforementioned type. (Many tube amps don't take tube rectifiers, but accept internally mounted solid-country rectifier diodes instead. These rarely fail, but if they do, replacement is definitely a chore for a pro .)

Speaker Replacement

There'south no room here to discuss why you might desire to change your amp's speaker, or what you should consider swapping it for. Simply bold yous already do want to swap it out, and have selected a suitable replacement speaker of the correct impedance and power-handling ratings, this is very often a job you tin exercise yourself. Here's how you generally go about information technology, although if there are any complications to these basic procedures don't force anything or risk breaking any components— seek professional help .

Speaker cable connections on a 1960 Premier Twin-8

Remove any dorsum panels on the combo or extension cab that restrict your admission to the speaker.
If in that location are any tubes hanging in the manner which either obstruct your admission, or which might be damaged if the speaker hits them on the way out or into the cab, note their locations and advisedly remove them.
Brand note of which of the speaker cables connections—positive (+) and negative (–)—are continued to which speaker terminals, marking them with a Sharpie if necessary, and loosen whatever button-on clips by gently wiggling them back and forth until they sideslip off the terminals. (Some clips have a "lock" tab that might require use of a small flat-head screwdriver to lift the tab from a notch in the speaker final.)
Using the correct size screwdriver or socket wrench, loosen and remove the mounting bolts or nuts that hold the speaker to the baffle (the piece of wood onto which it is straight mounted). Work in an X pattern by first removing ane, then going on to the one straight across the speaker from information technology, and so on. When they're all removed, put them safely bated.
Carefully lift the speaker and remove information technology from the cab, and set information technology safely aside.

Speaker mouting bolts on a Harmony H-306a

Lift in the replacement speaker, being careful to line up the mounting holes on its frame with the holes or bolts in the speaker baffle. If bolts are permanently set into the baffle for speaker mounting, exist very careful to line up the speaker's own mounting holes with these before lowering the speaker into place, to avoid puncturing the newspaper speaker cone with a misalignment.
Replace the mounting bolts or basics, reversing the procedure used to a higher place to remove them. Don't over-tighten these or you lot'll risk bending and distorting the speaker frame. A adept guide is to become them "finger tight" with your bare fingers, and then use the appropriate tool to tighten them another half or three-quarters of a turn.
Adhere the speaker cablevision, being careful to correctly align the + and – connections.
Replace whatever tubes and/or panels removed at the start of the procedure, and fire information technology upwardly.
Note that most new speakers require some breaking in, which can take several hours of playing, but also begins with the first time y'all turn on the amp. Let some base-level amp hum run through the speaker for a minute or ii before you play, so play gently and rhythmically at a relatively low volume level for several minutes to warm up the voice coil and the rest of the speaker'southward components before striking it hard.

Blowing Fuses

This is a relatively mutual fault that tin exist extremely frustrating, and generally goes one of 2 ways regarding whether it's an piece of cake user set, or something you lot need to take to a pro. Showtime off, though, exist aware that you should always supercede any fuse with ane of the same type and rating (and check the printed data on the amp itself, usually right abreast the fuse socket, to ensure that the right fuse type was in there in the first identify), and never use a fuse of a higher rating, which could run a risk serious internal impairment to the amplifier.

Fender replacement amplifier fuses

If your amp has suddenly started burning through fuses and it has a tube rectifier, try replacing the rectifier with a new tube of the same type, then pop in a fresh fuse of the aforementioned rating, and come across if that does the fob. Probably four out of 5 times that I've had an amp start blowing fuses more frequently than it should information technology had something to exercise with the rectifier. (Be aware, also, that some new rectifier tubes tin be subject to early demise right from the factory, so even if you feel confident it was a "new tube," try another to see if that'southward the source of the trouble.)

If that doesn't practise it, or if your amp has a solid-land rectifier, persistent fuse blowing is the sign of something more serious going wrong inside—a short in the ability supply, internal component failure, or possibly a trouble inside the power transformer—and the solution becomes a chore for a pro .

Pro-Job Checklist

That leaves you lot with plenty you tin can exercise yourself to keep your amp running smoothly and sounding its best, and to cheque and correct small operational problems. Here's a list of general maintenance and repairs that are, on the other mitt, definitely jobs that should be done by a trained professional, forth with the "tip-off" that might indicate the source of the trouble.

Replacing filter capacitors (tip-off: declining depression-end response and solidity, increasing 60-cycle hum, or dissonant "ghost noting"/following harmonics).
Tightening pins in tube sockets (tip-off: occasional crackling sounds or intermittent racket or volume changes, indicating poor preamp-tube pivot contact in sockets).
Internally cleaning or replacing potentiometers (tip-off: "scratchy" or racket volume or tone controls when turned, low spots or drib outs in these controls).
Replacing power or output transformers (tip-off: frequent fuse blowing, total loss of ability or output book).
Replacing components on excursion board, or entire lath (tip-off: well... merely most anything that might go wrong with your amp).

If you lot like the thought of doing equally much user-attainable maintenance as you can handle, seek out a good volume on the subject to learn about all of the above procedures in greater item.