My blinkin amp keeps conking.....

[ecca]

Marshall JTM 60, 12 years old has suddenly started blowing the HT fuse sporadically, 500mm slo blo.
I replaced the EL34s with 2 Harmas from Watford, it still does it.
The HT voltage is 493 VDC with nothing being played.
I suspect the HT smoothers which are rated at 550VDC but the only ones I can get are 500VDC which I don't think is enough headroom on the working voltage.
Any ideas ?
I've asked Amanda, she's probably still in bed.
Cheers
Ecca

[Twang46]

Hi Ecca

Was just looking at a site about these amps last night strangely enough

http://www.thegearpage.net/board/showth ... p?t=210069

interesting reading & loads of links

If you have a decent meter you could stick that across the fuse contacts (fuse out) & see what happens at switch on, inrush current can be higher a lot than you might think.

http://www.justradios.com/axialelectrolytics.html

for some higher voltage caps might be useful also

Cheers

Dick

[ecca]

Thanks Dick, useful tips and great links.

[David Martin]

Ecca: Just call the Marshall service dept and make an appointment to go to MK. They will fix it while you wait and guarantee the work too... Fantastic service...

"All Marshall service work in the UK is carried out at the Marshall factory in Bletchley. We do not have any other service engineers or centres based in the country. To have your amplifier serviced we can arrange collection from a business address, you can make an appointment and have it looked at while you wait or you are able to leave your unit with us. Please contact our Returns Department on 01908 375411 if you would like to arrange collection or make an appointment. You will be contacted with a free quote before going ahead with any repairs but we cannot give an estimated cost before seeing the amplifier. There will be a carriage charge if our couriers collect and return your amplifier and this will need to be paid regardless if you go ahead with the repair."

[Mark Burton]

Amanda's woke up now but busy in the General section .....

[ecca]

The capacitors are impossible to get.
I've ordered some 100uf @ 350VDC to put 2 in series to get 50uf @ 700VDC.

[neil2726]

Its probably full of crumbs from all those cobs!

[ecca]

My amp never goes out of doors these days, I use the wonderful Ampworks into some bugger else's amp.

[Amanda]

Ecca Wrote:

"My amp never goes out of doors these days, I use the wonderful Ampworks into some bugger else's amp."

Yes- for the last two weeks my fiery little Pro Junior Copy - boy is it loud, and if it will withstand Ecca then it's bomb proof
I'm now registered with Marshall as an approved service tech, allowing me access to spares and service manuals.

[ecca]

Capos fitted..... HT 493 VDC.......... see how it goes.