My blinkin amp keeps conking.....

[ecca]

Aaaaah ! Been on 10 minutes and current crept up to 300ma..........

[Risky]

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)

I once spoke to a firemen who had just attended a house fire caused the someone putting one of these "special" fuses into his 30 amp fuse holder.

Unbelievable...

Don't do this at home, kiddies

[ecca]

Don't be such a spoilsport Phil.
Current dropped back to 240ma now, wonder why ?

[RayL]

Ecca

Another idea.
Your Marshall uses dc biasing. If that dc varies, it will change the current drawn by the output valves. Check the dc bias circuit for dry joints and dodgy diodes/capacitors/resistors. Oh, and if you have a digital voltmeter,that would be better for measuring the bias voltage, because you don't want the AVO meter to load the circuit and mess up the reading. The AVO 8 has a higher ohms per volt than the AVO7 that it replaced but it's still not that high.

Oh yes, and the dc bias will of course be a negative voltage.

Ray

[ecca]

The AVO 8 is just for the current, it has a handy trip-out at the end of the needle's travel if there's an overload.
All voltages are measured using either the Fluke scopemeter or an AVO DA2001 digital meter.
I've ordered a set of ECC83s, in for a penny..... I've had the amp for 13 years with very little attention and there's no panic now.

[ecca]

Fitted capos- HT fuse still blew on switch-on.
Fitted new set of ECC83s- fuse still blew on switch-on.
Not always, but enough to be a nuisance.
Standing current never more than 200ma.
Latest solution is http://uk.rs-online.com/web/3305358.html
which appears to work a treat.
A little unconvential but I had one in the shed gathering dust so it costeth me nothing.

[MdL]

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

I wouldn't do that, it's just not safe. If one cap is (or gets) out of spec, they will blow up.

cheers,
Martin

[David Martin]

Would have been up and running weeks ago if you'd taken it down to Marshall's service dept...

[ecca]

No panic David, I don't use it much now.
It passes the time playing around with it and...... now I'm retired, I'm skint !
Sod Marshall, I'll do it myself which the latest soft starter appears to have done.
Although I'm still not entirely happy with the volt drop.

[ecca]

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

I wouldn't do that, it's just not safe. If one cap is (or gets) out of spec, they will blow up.

cheers,
Martin

I hardly think they'll blow up.
Besides, that same logic applies to every component in the amp.
In fact they work fine.