Audio and Video Talk > Valves / Vacuum Tubes

Valve etiquette and care

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Please keep the tips coming... and maybe some on the maintenance side...
Thanks in advance  :thinking:

All is not that glum.

The heaters in valves are actually quite shock-proof as they are sturdily 'packed' inside a cathode (the glowing tube seen - not talking about the old directly-heated stuff still used in some S.E.T.s). Do remember that WW2 was won with valve equipment ....

The envelopes are normal glass; no need for special gloves. It is well though to keep too many fatty sticky fingerprints off; they 'burn in' and look ugly (power valve glass temperatures can reach 270o).

No decent valve amplifier should go unstable with no load (there is/should-be a built-in load resistor) .... but yes, not all valve ampliifers are that decent. (...and there are at least an equal number of semi-conductor ones also not liking that!). Short the output of some SS amplifiers even for a fraction of a second and they are gone - not so with valve amplifiers.

I am unsure as to why switching on/off should be done in a certain order of things or without signal; not to my experience - enlighten please? (Again, they are actually more rugged in that sense than many SS ones. The 'road-to-fully-on' is actually more quasi-unstable with many transistor amps, what with the high degree of NFB often employed.)

Heat: One might keep in mind that maximum valve dissipation values (EL34: 25W;  6L6GC: 30W;  KT88: 35W etc.) refer to 25oC ambient (as it does for most electronic components). The greater danger is to the components warmed by valves in the vicinity, like electrolytic capacitors. And then keeping the glass clean also assists in cooling. A valve covered in muck cannot radiate as well as a clean one. In fact, a good idea to keep all electronic stuff clean - and also occasionally blow out the dust inside your PC monitor! (being switched off, of course ...) A layer of sticky dust inside a 20 year old valve amplifier begins to provide other paths for the electrons.

How does one clean a really filthy amplifier? You take out the valves, and dunk it into a bath with hot water and some Sunlite liquid or Mr Muscle (not oven cleaner), and scrubb with a brush!! Then wash/rinse all off thoroughly, and let it dry, even more thoroughly!! - before going back to operation. (This is time consuming, also watch out for moisture in unpotted transformers and such - might have to take the covers off or so - blow,  :blah:.)

Valves are sensitive to heater over-voltages. It would seem that some models from the east do not have their transformers correctly aligned. I have measured 6,9V heater voltage instead of the usual 6,3V. If mains tappings do not allow the right adjustment, the only way out is the rather inelegant way of adding low-value resistors in the heater circuits. It might also be done in the primary. Sadly that influences the power supply 'stiffness' slightly - not too important in valve amplifiers. But heater over-voltage (I mean substantially) drastically shortens valve life, particularly power valves.

Kent Kassler:
Ampdog....interesting to read re heater voltages.....currently have an amp that shows 5.8 volts for the 6.3volt heaters.....what would be the problems as a result of this?Thank you.


--- Quote from: King_Julian_S on July 24, 2013, 09:30:44 PM ---Mr W
Any ideas on where to source such cables ?
I use a normal kettle type plug , but I also get dead quiet response when volume is all out... And the speakers are very high sensitivity drivers as well.

I do get a very slight " Doooof " sound when I flick those switches I mention above to the on position...

--- End quote ---

I keep the lowveld audio screened mains cables and recommended gold props and Schurter IECs.

The reason for the switch on and switch of sequence is to never unnecessarily amplify any switch on thumps from gear further up the chain.

IMO as long as the power amps are switched on last and switched off first the others don't really matter.


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