Restringing

Guitars: On vibrato (tremolo) type bridges, restring one string at a time. This helps to keep the guitar in fairly stable tuning. Use lemon oil or similar and a clean rag on fretboards to clean off the dirt and polish the frets.
Tuners such as Fender with the slot at the top of the peg,  first bend a 90 degree angle into the string (about 3 inches beyond the high E peg and 2" for the low E) then cut off about 3/4" beyond that bend.  This bend helps to prevent the string outer wrapping to become unraveled, which can work its way down the string and cause intonation errors, loss of sustain, buzz and sound changes. Insert bend into slot and wind.
If using Sperzels, or other locking tuners, do not pull tight. Simply insert and push gently while locking down. Only about 1/2 a wrap is needed. 
Single hole only tuners: insert the string (observe the 3" and 2" rule) and bring it back around 1/2 way and bring up from under the string, so that as it tunes up the string tightens over the end brought thru (Martin Guitars recommendation and one of my favorites).

Basses: Same as guitars but add about an inch overall due to the wider tuner posts. The pre cut bend is more critical with these strings as an unwrapping bass string sounds quite abnormal not to mention an expensive re-do.
 

Truss rods: They are usually found at the headstock of Les Pauls or at the body end of the neck of classic Fenders. A truss rod gently corrects the pull that strings will exert on the neck. When adjusted properly, there is a balance between the amount of forward bow (relief) and the string height (action). The geometry of the string should show a consistent angle of deflection as it is fretted all the way up the neck, hence the need for some relief no matter how close you want the action! A good rule of thumb is to set the saddle height (bridge height on Tune-O-Matic style bridges) so that the strings do not fret out when bending beyond the twelfth fret (but as close as one can get), and then adjusting the truss rod so bending is just clear on the lower frets, or until you are happy with the amount of string buzz as it relates to picking strength.

Saddle height: Keep these oiled occasionally. Use the proper tools like hex wrenches or jewelers screwdrivers.

Tuners: Make sure they are tightened and oiled.

String Nuts: A string can bind in a dirty or improperly filed nut. Quick trick for strings binding at the nut: Pull strng back and forth in the slot a few times. Clean the slot with some floss, and then scrape a little pencil lead into it. Otherwsie purchase a set of nut files and do it like a professional.

Intonation: The actual length of the open string. The saddles adjust back and forth for this. A simple setting would be to play the string open and use a good electronic tuner to tune it. Then play it again at the 12th fret. If it is too sharp, pull the saddle back (increasing the length of the string) until it plays the same note both open and at the 12th fret using the tuner. Check again at the 17th fret. Be aware of magnetic pull from the pickups and eliminate it by lowering them.  

Pickups: If they hum it may simply be the pickup design. Single coil pickups will hear stray EMF's and there is little you can do, so either lower your gain or roll back the Vol pot fast when the tune is done.

Otherwise if you suspect there is noise coming from elsewhere, try shielding the inside cavity with sticky conductive foil (preferred) or conductive paint. In a pinch you could use aluminum foil glued with rubber cement. Be sure to ground it to system ground (shield of the output jack).

If you unhappy with your single coils, try replacing them with major brand replacement hum cancelling pickups (Duncan, DiMarzio, EMG, Barden, Lace, Fender etc).

Some single coil pickups are "reverse wound". This means they will mix with another compatible pickup and cancel hum.

Controls: If crackly: clean with control or tuner cleaner found at Radio Shack or Stewart MacDonald. Make sure the can says "Safe On Plastics". Careful not to inhale.

Normally the bridge is connected to the ground. Check this with an ohmmeter.

Speakers

Calculate Ohms (Impedance): Cabinets cabled together via their jacks on the back are considered to be in PARALELL. The easiest method for calculating impedance is to take two like cabinets, e.g.: 8 ohm cabs, and divide that number by two, e.g.: 4 ohms. Dissimilar impedance cabs, or more than two cabs or speakers wired in PARALELL require a formula that is thus:

___________1____________
(1/R1)+(1/R2)+(1/R3)...

<!The formula that states you can multiply the impedances and
divide by their sum only works for two spkrs!>


 




Speakers inside a cabinet can be hooked in SERIES by connecting each one in a daisy-chain (terminal of one spkr. to terminal of next). This is simply additive, e.g.: two 8 ohm spkrs. will add to 16 ohms. A 4-12 cab usually has a pair hooked in parallel and then those hooked in series with the second set which is also hooked in parallel. If they were all 8 ohm spkrs. then the total would be 8 ohms (the two in parallel becomes 4 ohms and two of those pairs in series adds to 8 ohms.).

When removing power tubes to "brown" down the power, one must not only be sure to remove the two outside tubes in a four tube configuration (such as Fender Twin) but also to half the speaker load. For example: you remove the two outside tubes in a Marshall head, then take the normal speaker requirement (eg; 16 ohm tap) and plug in the equivalent of half that (eg; 8 ohm load).

In PA applications it is generally better to use an amp that is rated more powerful than the speaker is rated because when a solid state amp distorts unnaturally it produces DC current which burns up any voice coil, and more powerful amps tend to remain clean while speaker is brought to its full power rating. A distorted speaker is easy to hear and can be caught before it burns or rips up, but a distorted power amp will burn up a speaker very quickly. Pre amp distortion is a different animal and is not considered to be near as harmful as power amp distortion.

 

Hope you have found this info useful. Consider it a gift; a jewel in the muddy pond of life, where avarice, greed, and profit are oftimes prime motivators. Pass the good word on...