Frequently Asked Questions -Valve Amplifier repairs

We’ve compiled some common discussions when valve amps are brought in for repair.  I’ll try and answer some of the popular questions asked….

Q My valve amp is not working i think the valves are ok because they have an orange glow, this means they’re working right?

A Unfortunately the heater of all valves glow orange and doesn’t mean the valve is actually working, all it means is the heater works.  In a valve the heater is the generator of electrons and has no reflection on the vacuum, the grid or plate condition.

Q My valve amplifier feeds back and squeals when i turn the volume or drive volume up to high what is up with it?

A This is a problem quite often with the preamp valves becoming microphonic, the valve amplifies the vibrations and induces this on the output signal, it becomes a circular problem and before you know it, it squeals.  This can generally be rectified by replacement of the preamp valves typically a 12AX7 or AU7, EEC83.

Q I’ve not used my amp for a while and I’m sure it didn’t hum as much as it does now, is it me or is there a problem?

A The storage capacitors do dry out over time as they contain a liquid impregnated into paper or plastic. Think of the storage capacitors as a water tower keeping the reserve of water or power ready for the amp, when they dry out this is like lots of tiny holes in the tank stopping it from keeping as much of the water resulting in less storage of the power.  We stock branded capacitors generally rated at 500V  and are most often in the values of 22uF, 47uF and 100uF