I get a ticking sound on one or both channels

[FAQ Team]

This can be caused on WAD amps by the OP TX frame not being earthed to chassis. Consequently there is a build up of static electricity, which finally gets so great it arcs over to the chassis, causing a tick in the loudspeakers. Although the voltage may be very high it is extremely low current and poses no threat to mind and body.

The solution is very simple, wire one of the mounting bolts or the cover to the earth terminal.

A second cause may be intermittent breakdown of a coupling capacitor. This may be more of a pop. It may be caused by the capacitor film arcing and the capacitor "self healing" as that area of the film burns away.

Check the voltage rating of the coupling capacitors, particularly allowing for any higher switch-on voltages when the valves are cold and not conducting. Substitute capacitors in the offending channel to isolate the problem.