As soon as somebody (usually somebody trying to sell me something) sets off with “This ECC83 (JJ…EH…Groove Tubes…Mesa…TAD….etc…etc…) has a great, really tight bottom (?), a very cool detailed mid range, a glistening array of shimmering highs”; I go into ‘dark cupboard mode’, and check the bike lock on my wallet.
Were I a NORMAL, say, twenty-year-old, (are there any of them? Were there ever any of them?), my top end range of hearing would fall just a bit short of a dog whistle. Around 20kHz. As I’m not any longer a twenty-year-old (being rather closer to a hundred than twenty) my hearing falls off at around 14kHz in the right ear and nearer 11kHz in the left. So, obviously, there is little point in sales pitching me a valve with ‘shimmering highs’ if I can’t hear them.
Extrapolating this logic, how does anybody who sells valves in Russia, or Watford, or wherever, expect to tell me (or anybody else) how we hear this, that, or the other? Bullshit and bollocks? It starts to smell like it, don’t you think?
So when might we need to swap valves? And this is not a simple question, because there is no valid answer like, say, every year or every two years. I have a 1963 Fender Tremolux amp that is completely original. Which means that the valves, and everything else in it, are 50+ years old. It still sounds great. And here is the downside of revalving an amp. The valves in your amp acquire a character (as does the rest of it; speakers, capacitors, even resistors and transformers) which becomes an irreplaceable unit. It becomes a unique piece of electronics even after a year or two, and certainly after fifty years.
The tell-tale signs that valves need replacing are not difficult to pinpoint, generally.
A loud buzz that isn’t affected by the controls……look at the power valves. The grey anodes (the metal box inside the valve) shouldn’t glow. Glow either end is ok, that’s the heater. Switch off. A valve change (all the power valves as a matched set), but don’t fit them until you’ve had the amp’s bias circuits checked. If that has a problem, your nice new valves will be destroyed, more or less straight away.
Loud hums that might (or might not) be affected by the controls, are often caused by a preamp (ECC83, say) valve fault called ‘a heater-cathode short’. It means the heater has distorted and shorted to the cathode. Change the valve. You can isolate this by removing the valves one at a time.
Whistling, ringing noises. If you tap the side of a preamp valve with pencil, a microphonic valve will ring. This can also happen with power valves. Change it (them).
Just gently moving the valve around in the valve base can often clear poor contacts on a valve base. Worth a try.
I’ve just been tapping this mug of tea with a pencil and it sounds great. The macaroon didn’t. Must be faulty.