repairs to guitar amplifiers & hifi amps

 REPAIR CHARGES

• Testing prices range from £15 - £50. Minimum labour charge is £80. The testing fee is deducted from the final charge if the job goes ahead

• In most jobs a deposit is required, all work is guaranteed, and service reports given upon request

• Often faults and diagnosis are straightforward in which case a minimum fee labour charge can apply

The main issues that affect repair are design faults, long term use and/or abuse and equipment which has been quickly and badly repaired or modified.

REPAIR PROCESS

• Fault diagnosis: visual inspection, AC/DC measurements, signal tests, component tests

• Remedy : Replacing faulty components, cleaning and tidying up

• Testing : At full capacity plus necessary adjustments i.e. biasing in output stages etc

VALVE AMPS

There are factors to be considered when restoring and repairing a valve amp which has been used a lot over the years. Pubs, recording and rehearsal studios can be hot and humid places. The amps get hot during use and then cold when they're left in a car overnight, they also run on dangerously high voltages. Safety must be taken very seriously. There are also design faults associated with modern tube amps.

Sometimes amplifier repair is complicated due to intermittent and knock on effect problems. Therefore thinking time is needed, especially with design faults where modification might be necessary. Old used amps may require restoration work.

SOLID STATE AMPS

A schematic diagram is needed for quicker fault diagnosis. Design faults are not found very often because unlike valves, transistors fail as soon as their maximum power ratings are exceeded. Also deterioration of materials is not as serious (as in valve equipment) and most of the circuitry operates at lower voltages.

Where catastrophic faults have taken place in output stages however, full pcb reconstruction and rewiring might be necessary. Transistor circuits are more electronically complicated and sometimes it takes longer to find the fault. Due to printed circuit board design, in most cases, solid state (and sometimes valve) modern amps must be completely dismantled in order to replace one or two components.

Problems are more unpredictable in transistor equipment and in output stages knock on effect, catastrophic faults are often seen. There is more diversity in solid state than tube electronics design. Full restoration may not be necessary in old transistor gear provided the safety issues have been addressed. There is room for improving reliability though. For instance, in output stages removing and cleaning the heat sink from the old silicon compound and replacing it with new compound, will improve thermal bonding between semi-conductor and heat sink. Also, since potentiometers and switches are screwed on the front panel and soldered on the pcb, it might be a good idea to remove them individually clean them with special switch cleaner. The old solder is removed, the print cleaned and the component resoldered etc.

In hybrid amps anything might be necessary from a simple repair to a full reconstruction if the equipment is very old. Old transistors are very hard to get these days. In modern equipment like Marshall Valvestate the work is a lot more straightforward.