Tube Amps and the Freezing Cold

I suppose this one's from the "do as I say not as I do" file. This is what can happen when you leave your amp in the trunk in the freezing cold. I was playing a gig that ended in the middle of a snow storm and I left my amp (a custom thing built on a Teisco Checkmate 50 chassis) in the trunk for a few days.




In the morning the trunk got warm enough for water to condense on the cold transformers and then got cold enough for it to freeze there.

Of course one would worry about rust and moisture damage, but the real danger here is not the frost and condensation on the transformers. It's the danger of the amp being switched on with that condensed water shorting the circuit inside the amp.

This can happen as a result of condensation inside the chassis or by water dripping there from the outside. Switching an amp on in this state is a great recipe for arcing and damage inside the amp.

If you are gigging in cold weather it's a very good idea to keep your amp covered in the trunk or van and ideally keep it covered while it comes up to room temp to avoid condensation. If you bring a cold amp into a warm humid room it will come up to room temperature in a fairly short period, but the water that condenses on the cold transformers and chassis can remain for hours or more. The above picture is of an unusual case. Remember, the condensation generally occurs after the amp has been brought inside. It may be perfectly dry coming in from the van. After 10 minutes in the indoors it can become dripping wet.

Now of course this has been happening to amps for decades and they haven't all gone up in smoke. But the danger is there. If you really want to play it safe you could build a simple series outlet current limiter and keep it in you gig box. Use that when you warm the amp up (and dry it off) after a particularly cold trip.