My blinkin amp keeps conking.....

[cockroach]

Hello Ecca,

My Marshall 60 doesn't do those sort of things..

but then, it's a TRANSISTOR amp, innit?....

[ecca]

Yes ......crap.

[ecca]

Right.... progress report.
It still blew the 500ma HT fuse after the 47uf/550VDC smoothing capacitors had been replaced by 2 off 100uf'350VDC capacitors in series
to give me 50uf @700VDC working.
I measured the AC surge first with my AVO 8 which showed little more than 200ma on switch on , steadying out at approx 150ma.
I then measured it using an Isotech current transducer into my Fluke 123 scopemeter which showed an off the scale peak but only microseconds.
The steady current on this showing 180ma.
These are from the HT secondary of the transformer and are AC readings.
The HT DC voltage again using the Scopemeter peaked at 536 VDC steadying out at approx 500VDc as the heaters warmed up.
There's not a lot wrong with it.
I shall replace the 4 rectifying diodes with 1N4007s, each 1amp @700 volts capability and I've ordered a different type of 500ma anti surge fuse.
I'll let you know.

[RayL]

Ecca

Have you checked the EL34 valve bases for any signs of charring or tracking? A spark that jumps between pins (when hitiing a loud chord, for example) can leave a carbonised 'track' and this makes a further spark more likely. The spark draws enough current to blow the fuse. Under these circumstances, even the weather can make a difference. Recently it's been dry, but in wet weather with high humidity it's easier for sparking to happen.

Ray

[ecca]

The valve bases look clean Ray.
I've now switched it on and off 12 million times with the Avo in place of the fuse and it would appear to be
the switch on surge that's the problem.
The voltage, when stabilised as the valves warm up is around 500 volts and it doesn't fluctuate.
The current steadies at around 150ma ( AVO ).
The amp is fine without the fuse in !
I'll leave the AVO connected up.

[rogera]

Ecca you could always araldite the Avometer to the top of your amp with the scale facing the audience just to look 'cool'

or........... you could fit one of the special fuses that I can supply (at the right price of course)

[jimuc]

Ecca you could always araldite the Avometer to the top of your amp with the scale facing the audience just to look 'cool'

or........... you could fit one of the special fuses that I can supply (at the right price of course)

Loved that Roger...........Haven't laughed so much for ages (Must get out more)
Don't know what Ecca might think though
Cheers
Jim

[Twang46]

Hi Ecca

Ceramic fuses are usually far better at coping with high inrush currents

http://www.europacomponents.com/product ... prd_id=917

You could always pop into the nearest B&Q for some 30amp fuse wire, increased transient definition, better bass......................however not so good at mundane stuff like protection though

Cheers

Dick

[geoff1711]

Or being really boring you could pop it in the back of your car and take it on a day trip to Milton Keynes, I've always found them really helpful back at the factory.

Geoff

[ecca]

tee hee to you all......

Please send 1 fuse Roger, should be enough.