Outdoors with a tube amp
I play a regular outdoor gig throughout the Summer here in the UK which has my trio set up under a band stand with open sides but overhead cover. I have recently purchased a tube amp and it got me thinking if outside playing can damage a tube amp. The gigs are May - September and many of them are in the evening finishing at 10pm.
I have read many times about letting a tube amp reach room temperature before turning it on and letting it cool down before taking out into the cold. The weather on some of these gigs can get quite cold when the sun goes down and I can remember from recent years occasional dampness in the air. Will it be harmful to my tube amp in these situations or is it only winter type cold conditions that will cause problems? The soft case that came with the amp head is very padded so I am thinking that it will help to put this on when I have turned off my amp.
I would not worry about anything other than rain. Tube amps were used in the American south in the days before air conditioning was common. Ain't got nothin' like that on your island. Now volcanic dust....
In essence, unless this is a vintage amp you have the only difference between a valve amp and a solid state amp is the valves. Older amp's though may well have components that are more prone to humidity, temperature etc.
While in many cases the general advice is to let valve amp's warm up, this is to ensure all the valves are at full working temperature to ensure the sweetest sound. Your case is a little different though. The danger here for you is that large and fast changes in temperature tend to put stress on the valve seals (between the glass and metal contact pins). If these seals get overstressed then the vacuum can escape and the valve will go "soft" and performance will gradually decline. Relatively slow changes in temperature cause nowhere near the same stress to the seals.
I think the best advice I could give is to be aware of this and carry on - valves get a fair amount of this thermal stress every time they are turned on anyway. What I would say is once you are set up and turn on, then leave the amp either on or in standby until you have completely finished the gig. Not turning off when you take a break will minimise the heat cycles and improve reliability.
Also as Bob says, rain is another matter and has nothing to do with valves!
P.S. ..and yes, putting the cover on when you finish will allow the amp to cool more slowly.
As the others have said, I would not worry too much, as long as you treat the amplifier sensibly. Since the cabinet is self-heating once the amp has warmed up, it does not matter too much what the outside temperature and humidity does, as long as you keep the cabinet out of the rain.
The thing to avoid is switching on from cold if the amp has been standing for an appreciable time in a damp atmosphere. If you can, keep the amp in a dry environment (e.g. in the car) until just before setting up and switch-on.
Just to add to what Boswell said. The main thing is to avoid any condensation inside the amp. This is important too with solid state amp's but the higher voltages generally in a valve amp are likely to cause more problems. Just avoid condensation with any electronics and don't turn on anything you suspect! Also a final thought, once you have finished the gig and put on the amp's coat on, get it indoors (or in the car) as soon as possible too.
Thanks for the excellent replies as always. Your answers have put my mind at rest.
I now look forward to a Summer of tube tone!