Limited use?.

[catch29]

I've acquired some old faulty transistor amps and tuners. Having used a lamp limiter on valve equipment (after visual checks) I read somewhere that it is of limited use (no pun) on transistor units, is this correct?. What's the alternative, a 1 amp plug top fuse and RCD?. Your thoughts please gents & ladies.

[Murphyv310]

Hi.
If they are faulty I'd do cold checks and a visual inspection prior to powering them up. Go over power supplies firstly looking for short circuits, shorted rectifiers, look for bulging caps and burned resistors.
Old transistor equipment with a linear power supply can be run low on a variac but those with a SMPS is a different kettle of fish. Some SMPS do not like low voltages.

[Mike Watterson]

Even valve gear I'd only use a lamp limiter on very dodgy looking series heater live chassis, or valve TV.

Cold inspection etc as Trevor says ^^^^.

Some transistor PAs can be damaged by low HT. A SMPSU will attempt to maintain o/p and take high currents on a variac.

An RCD is of no use. A low as possible fuse according to power rating, even 100mA or 500mA.

Check HT and speaker drive point of transformerless push pull.

[Ed_Dinning]

Hi , if it is a transistor amp with lower voltage rails and you have a low voltage power supply, preferably with current limiting then use it to power the amp, bypassing the mains power supply.

Ed