Tubes going bad in storage?

Collings

I've had one of my amps in storage for 2 to 3 years and although I say in storage I have powered it up every few months and left it on for 15 mins or so without playing through it just to check it was ok and I was worried about the caps if I just left it 

I've powered it up today and it makes a loud hum/cracking sound. I did some fault finding and it looks like the output valves are faulty (2 x EL84) as when I swap them for a spare set all works ok. I've swapped back and forth a few times and the problem always goes away with the spare set of valves fitted. I've tried cleaning the original valve pins with contact cleaner and wire wool but the issue does not go away with the old valves fitted so I have reached the conclusion it is certainly the old valves that have developed a fault.

So my question is if this is possible given the amp effectively has not been used?

When in storage it has been kept in damp free environment with a cover on and not subject to large variations in temp.

normula1

Could be oxidation on the pins

Collings

normula1 said:

Could be oxidation on the pins

I've tried cleaning the old valve pins and sockets and problem still shows itself with the old set of valves fitted

ICBM

Yes, it’s rare but possible. It’s surprising that both have failed though - try one old and one new and you may find it’s only one of them. Keep the other one as a spare.

Collings

ICBM said:

Yes, it’s rare but possible. It’s surprising that both have failed though - try one old and one new and you may find it’s only one of them. Keep the other one as a spare.

Thanks that makes sense I'll give it a try