Cleaning your Guitar Amp & Information on Tube Valves and what they do.

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I've recently undertook to sort out why my guitar amp is crackling and popping and dropping out soundwise and thought I'd put up links to any good resources I found here in case anyone else was looking or had some tips.

My amp is a Laney LCII valve amp. My knowledge of valves is rudimentary at best. I know they do "something" to the sound of the guitar, but have no idea how or what to replace and for what reasons.

The info I've put below, I found very helpful and hopefully will be of use to people here.
Feel free to add any info or sites you think are helpful.

*****CLEANING YOUR GUITAR AMPLIFIER*****

CAUSES OF NOISE PROBLEMS:

Many of the irritating, sound-robbing problems that plague older tube amplifiers can be traced to dirt and oxidation that have accumulated on contact surfaces over the years. Dirt and oxidation deposits in tube sockets and amplifier controls cause unwanted distortion, loss of volume and a wide range of crackling and popping noises.
During the years that fifties and sixties tube amplifiers have been picking up value and a cult following, most of them have also been picking up sound- and power- robbing dirt and oxidation.
Airborne dust that settles in amplifiers is conductive and electrostatically charged. Dust deposits interfere with signal transfer between components, causing stray noises, distortion, and generally dissatisfying amplifier performance. The dust's electrostatic charge attracts more airborne dust, causing more interference with the amp's circuitry, further hastening amp failure.
Oxidation deposits on amplifier-control and tube-socket contact surfaces also impede signal transfer, causing unsatisfactory amp performance. Sewing machine and 3-in-1 oil foolishly squirted into amp controls fouls the components and attracts more sound-robbing dirt. The more conductive contaminants settle on amplifier surfaces, the higher the risk of arcing, current taking a component-destroying jump between normally unconnected electrodes.

In the worst case, dirt and oxidation can combine with moisture to cause the big "C", catastrophic failure: the destruction of multiple components due to arcing and consequent short-circuiting across a large surface of amp circuitry. In the usual -less drastic-case, dirt and oxidation rob an amplifier of power and clarity.

PREPARE FOR CLEANING:

Many amps brought in for repair only need this basic tune-up, and perhaps a tube or so, to get back into service.
It's a good idea to let your amp sit unused for a couple of days before the tune-up. This will give the filter capacitors some time to lose their charge. Letting the capacitors discharge slowly is preferable to having them do it all at once through your body while you're poking around inside the amp.

Having the supplies you need on hand makes the job go faster; you'll want screwdrivers, some contact cleaner (Gunk brand choke & carburetor cleaner and WD-40), a toothbrush and, unless you own an air compressor, an aerosol can of compressed air. If you know how to use them, soldering supplies and a volt/ohm meter can also come in handy, but aren't essential.

PROCESS OF CLEANING:
This can be used for most amps, the tube parts if you don't have a tube amp.

Start by unplugging the amp from the wall, the speakers from the amp, and removing the amp chassis from the case. With the chassis out of the case, you can locate the filter capacitors you'll want to avoid touching as you perform the tune-up. These will be cardboard cylinders (usually orange or tan or vintage Fenders) with "+" printed near one terminal. It's also a good idea to steer clear of wiring connected to the power transformer (that's the large, heavy one); it's a discharge path for the filter capacitors.

Start by cleaning dust and dirt off of chassis, component, and connection surfaces. Use compressed air to blow loose dirt away. For dust stuck to component and chassis surfaces, Csar works with a toothbrush in one hand and a can of compressed air. Don't waste time on crud that's leaked out of dead capacitors; it's there to stay.

As you clean off solder joints, examine each connection carefully to see if the wire is solidly joined to its terminal. Wires that wiggle loosely from their connections and solder joints showing visible breaks can degrade your sound. If you have a volt/ohm meter and soldering supplies, this part of the operation is a good time for checking circuit continuity and desoldering and resoldering worn connections.

Tighten down the power transformer screws. On tweed Fender amps, the only way that the transformers are grounded is through their mounting screws. A poorly grounded transformer can cause intermittence in the amp's output. You may need to substitute mounting screws one size larger than the old ones to restore a good connection between transformer and chassis.

With the underbrush cleared, you can start work on the tube sockets and tone and volume controls, areas particularly sensitive to interference from dirt and oxidation. You'll be using solvents and friction to clean contact surfaces. The cleaner you get and keep these surfaces, the louder and clearer your amp will sound.

TUBE SOCKETS

Clean one tube socket at a time. Take out the tube, spray contact cleaner, or Gunk followed by WD-40, into the socket, then re-insert it and shake it around in the socket to expose clean contact surface. Be careful with the spray, the idea is to use enough to clean the part you're working on, without saturating the surrounding area. If the socket was particularly dirty, repeat the procedure before moving on to the next one.

TONE CONTROLS (POTS):

Clean the tone and volume controls, potentiometers, or "pots", for short, by spraying contract cleaner through the openings in their covers. Spray in a little cleaner, turn the shaft briskly back and forth a few times, then flush with another shot of cleaner. If you're using Gunk, flush with WD-40 right after you spray the carburetor cleaner; leaving Gunk on too long can freeze the control shaft.

Re-mount the amplifier in the case and reconnect the speaker. Now that your tube sockets and pots are clean, you can troubleshoot your tubesa, another potential source of stray noise, distortion, and weakened sound.

NOTES ON TUBES AND TUBE AMPS

All tube amplifiers have at least one power tube (such as 6L6, 6V6, or 5881), and at least one preamplifier tube (such as 12AX7 or 7025). Most older amps will also have one rectifier tube (such as 5Y3GT, 5U4, or GZ34).

Drugstore tube testers can be used to tell if tubes are dead or alive, but they don't tell you anything about whether a live tube is causing sound problems. Tube problems that won't show up on a standard tube tester can be diagnosed in the amp.

With all the tubes in their sockets, the tube covers off, and nothing plugged into the amp inputs, turn the power on and crank all the controls up to maximum.

Troubleshooting rectifier tubes is easy; they're either dead or alive. If the rectifier tube lights up when you turn the amp on, it works.

POWER TUBES [6L6, 6V6, or 5881, etc]

A power tube that doesn't light up is dead for sure. A healthy power tube will light up and give off a medium-intensity orange glow. Don't worry about power tubes that give off a dull blue glow; they don't necessarily need replacement unless they have other problems.

Power tubes that glow bright red, however, are a sign of trouble. Try another power tube of the correct value in the socket. If the new tube still glows bright red, there is probably a failed component in the circuitry to that tube, and you should take your amp to a professional to get the problem tracked down and fixed.

Tap each power tube with our fingernail, tubes that send a loud, low-frequency noise through the speaker when they're tapped should be replaced.

Inspect the shaft on the base of each rectifier and power tube to make certain that its guide pin – the ridge that slides into a groove in the socket's center hole, aligning the tube pins with their proper socket connections, is intact. Incorrectly inserted tubes due to broken guide pins are probably the single most common cause of amplifier failure.

PREAMP TUBES [12AX7 or 7025, etc]

Use your fingernail to tap each preamp tube. If the tapping is amplified and comes out of the speaker as a loud, high-frequency noise, the tube is causing problems. If there's another socket that takes the same value tube, try the questionable tube in that socket. Because of differences in circuitry leading to sockets that use identical tubes, a tube that makes noise in one socket can work just fine in another. If the tube causes problems in all the sockets you try, you'll need to replace it with a new one.

SPEAKER CONE:

You can now check out the amp's speaker(s) as the last operation in your tune-up. Plug in your guitar and set the amplifier to a low volume; you won't be able to tell the difference between amplifier and speaker distortion at high volume. Slowly play a few full chords. If the speaker sounds distorted or gravelly it may need repair. Try the amp through another speaker (one you know is working right). If the problem goes away, go ahead and get the first speaker reconed.

GENERAL GUIDELINES

1) Protect it from dust by keeping it covered when it isn't in use.

2) You can slow down oxidation build-up by keeping the amp away from damp places and protecting it from rapid temperature changes.

3) Never power up a cold amplifier; let it come up to room temperature before you turn it on. Sudden heating can crack cold power tubes. Cold air inside the chassis condenses as the amp warms up, depositing moisture on component surfaces that can cause arcing and component failures.

4) Don't keep the amp anywhere you wouldn't be comfortable sleeping. this means you'll never leave your amp in a car trunk overnight or store it
in a damp basement.

5) Semi-annual tune-ups and regular attention to how you use and store your amplifier will keep it sounding sweet and strong, and save you the pain and expense of avoidable breakdowns

The above quotes are an edited version of the article found here:
http://www.kbapps.com/tubecare.html

The "Gunk" that is referred to is this:
http://www.amazon.com/CC3K-Carburetor-Parts-Cleaner-Basket/dp/B000ABGA4E

WD40 (In case you're wondering what these things actually do):
http://www.wd40.co.uk/index.cfm?articleid=1519





*****NOTES ON TUBE VALVES AND THEIR FUNCTION*****

Valves were the precursor to modern day transistors but have stuck around in sound producing amplifiers because they seem to “colour” the sound characteristics produced in a pleasing way to our ears.

PRE AMP TUBES:

The pre-amp section of a valve amp takes the relatively small signal from your guitar and amplifies it to a sufficient level to drive the power amp section.
And, along the way it also shapes your guitar's sound according to how the tone controls for bass, middle and treble are set. Most preamps will also allow the user to control the amount of gain [distortion] added. In fact, in modern amps, the amount of pre-amp gain on offer is often massive! The type of valves used in all Marshall pre-amp stages is the double triode ECC83 or 12AX7 [ECC83 is the English name for this valve, 12AX7 is the American - further proof that we are two countries separated by a common language!].

POWER AMP TUBES:

Once the pre-amp has beefed-up, shaped and [if desired] distorted your guitar's signal, it is then fed into the power amp which gives it the required physical clout to drive the loudspeaker system. In addition to adding further muscle to your guitar's signal, if desired the power amp of a Marshall valve amp can also be driven to the point that it also adds desirable, harmonic distortion and compression. called power amp distortion

One type of preamp tube is used in conjunction with another type of tube in the power amp section for technical reasons:

In the power amp section you'll usually find two types of valve being employed. At the input you'll find another double triode, usually an ECC83 [edit: PRE AMP TUBE], which functions as a phase splitter or inverter. Simply put, as its name suggests, this valve's job is to split your guitar's signal [which presents itself as a sine wave into two halves. Why? Because the beefy valves that make up the rest of the power amp [usually EL34s, EL84s, 5881s or 6L6s] work together as pairs in what is known as push/pull operation, that's why! The portion of the wave above the central line is dealt with by one power valve [or group of them] while the portion below is dealt with by the other valve [or valves].

Most of the info took from here:
http://www.marshallamps.com/resources/secret_life_of_valves/secret_life_valves.asp