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Hi all, a techy question!

I have an old Marshall amp head which has not been switched on in twenty years. I have been told that the caps are in danger if powered up in the normal way?
Is a variable power supply needed to power up slowly?

Since I haven't got one of these anyway, is there another way of doing it?

Any advice would be appreciated!

sixtiesman

Can you get the temporary use of a Variac voltage controller?

Running the amp for half an hour or so at half-voltage, then increasing the value in 15v steps every five minutes whilst carefully observing (and sniffing at) the chassis, should suffice.

Alternatively, get a good amp repairer to check the main components before he powers it up.

If you're not entirely sure or confident in what you're doing I'd suggest this goes to an amp tech. Electrolytic capacitors degrade with age so at the very least I'd get the electrolytics in the high voltage supply replaced.

You could use a 'light bulb limiter' which as it says, limits the voltage. You could make one of these yourself. This is a 'poor mans' Variac.
But as Roger says if you are not familiar with electronics it would be best to take it to a Tec.

I would like to thank everybody for their contributions. You are a very knowledgeable bunch!

I suspected that a variac was the answer, I haven't got one and I don't know anyone who has. The one man electronic shops where this was possible have all gone.......

I emailed Marshall and they replied with the variac solution.

I am aware of the light bulb arrangement, a friend of mine actually made me one. It only has one bulb socket and getting hold og 200w bulbs is difficult. I have read a dissenting account of how these don't work too well as the bump at power up is still there for a fraction of a second (?? )

Maybe an am dram spotlight rheostat?

I will post when I solve this.

Thank you again

Sixtiesman

With the amp not being switched on for twenty years the sensible action is to replace the electrolytic capacitors.

The argument for keeping amplifiers completely 'original' makes as much sense as keeping the original tyres on an old car!

In addition to having the amp sounding as it should you will benefit from better reliablity.