by peter roest » 18 Oct 2010, 16:00
1. You must know that after switching on, all valves are on duty. When using the EF86 channel only , the valves in the other channel are also using energy and get older.
2. There is a big difference between the load of the end valves (EL84) and the other valves. The EL84's in the AC15 are in class A "biased" (stationairy current at no signal) on 70-80% of the maximum current. The other valves are much lower loaded (10-20% of the maximum).
This means that the lifetime of the two types of valves are different.
The EL84's should be replaced after about 2000 hours, the other muchs at a more longer time.
For the Vox AC 30 the replacetime for the EL84 is shorter because the stationairy current is more than 80% they get very very hot (I use Sovtek EL84M(ilitairy) whith longer life time).
The EZ81 can be replaced when he is kaputt.
for example: I have a dynacord tape echo in function with valves older than 40 years.
Peter