or, do you polish it or play it? (ok, my cliche alarm just went off…)
Amplified music has now been going for more than eighty years, vintage gear like that used on classic performances has achieved stratospheric prices, and even pawn shop scores of previously thought less desirable gear are now valued from being used by famous players and appearing on notable recordings. And no one knows what gear will come to be regarded as ‘classic’ in future years… So how to approach repairing and/or restoring this stuff?
To me, it was made to played. If it can sound good, it should have that opportunity, not sit around silent.
Most of the best amps use pretty high voltages, and over time this kills components just like it can kill people: capacitors dry out (perversely, especially from under use), or leak dc; resistors drift in value, become hissy or even burn out; valves lose emission or short; transformers can also short-circuit. Often, these voltage-related failures can take other components down with them; at the very least the circuit tolerances will be exceeded leading to less than ideal operation.
Then there are the failures that just arise from usage and environmental factors: stressed jack sockets fail mechanically and no longer make proper connection (often then fatal for output transformers if they’re speaker jacks); poor original solder connections go intermittent or component leads fatigue (both can also be catastrophic for other components); switches and potentiometers become rough in operation and noisy; corrosion leads to failed ground connections; jarred valves get microphonic or their contacts loosen; speakers rub, blow or their cones tear; control knobs get bashed and fall off.
Electronics has evolved, economically rationalised, got safer and its chemical constituents more environmentally constrained – sometimes the specific parts or particular component values needed for repair are just not available anymore, so substitutes have to be used. Even the most professionally orientated pieces of gear were products of a business plan when sold, so were designed and made to a budget (and often the time constraints of the music industry trade shows’ cycle). They all had by default a design life, even if nobody bothered to think about it much in those terms then (and it’s the weakest component in an otherwise over-engineered chain that can set this). Many of the favoured circuits that have been used were lifted from quite different applications originally. Often the parts used were under-specified anyway, and not up to the demands of the equipment, or perhaps just the way it may have come to be typically used; possibly they aren’t (or never really ever were) even safe.
Practical upgrades consistent with retaining the original sound are sensible.
Guitars and basses can also suffer much abuse arising from their use; older instruments should always have any of their original parts that are replaced retained so that re-sale value is not impaired.
If you have a vintage or loved piece you want me to repair/service/restore operationally, we can discuss this and the approach to the work to ensure it is carried out sensitively with regard to the originality and value of the equipment. You are the customer, and subject to any overriding user safety issues, it’s entirely your gig.