Recent repairs blog from an amplifier repair company

We've created a blog of some of our recent repairs.  Rather than trying to fit them into a certain category they're just listed here most with pictures and a description of the fault and roughly the work done to repair guitar amplifiers.  We're happy for people to use the blog as a guide to repair as long as you are competent to do so.  Remember working on valve amplifiers contains potentially lethal voltages in excess of 500V DC, which is much worse than 230V AC from the wall socket. As a warning we must advise that it is unsafe to work on electronics unless you are skilled and confident to do so.

 

An Ashdown MAG 300 amplifier with a reported loud intermittent hum fault on the speaker regardless of volume control.  Initially the first point of call is to measure the speaker terminals for any DC appearing on the output.  Any significant DC on the speaker output will generally make a hum.  This amp all seemed clear.  A great little workshop tool is a small insulated screwdriver, lightly tapping on the circuit board often reveals all kinds of issues, microphonic capacitors, bad joints, broken legs.

Suspecting a storage capacitor issue because of a) the lack of DC on the output, b) significant hum the power board was unscrewed.