Vox AC30 CC2X Output valves

[phil335]

Hi new to this forum stuff
Does anyone know if any damage will be done if I put 2 different matched pairs of EL84 valves in the output of my Vox AC30 CC2X instead of a matched quad set?

THankx in the hopes of an answer!!!

[pdf64]

Unless the 2 matched pairs are reasonably close on current draw, then 1 pair will run hotter than the other pair. On an ac30, where they're running at/above max plate dissipation, the hot pair may run over their max, so have a short life. If they fail so as to become effectively open circuit, then the other pair will lose bias (bias on an ac30 depends on all 4 el84s operating in a similar range).
If you have to do this, then switch it to the 82ohm cathode resistor option.
Also, hum may be caused if they aren't split evenly either side of the output transformer, ie AABB bad, ABAB/ABBA/BABA/BAAB good.

[phil335]

Many thanks for the reply. Makes sense, will use matched quad set now!