DrNomis wrote: phatt wrote:
I have no idea as to which models this refers ,, But I did read way back on AGGH (I think)
that some of the later marshal's had inferior circuit board material that actually absorbed moisture.
And you do live in one of the most humid places in Aust. The symptoms you describe could well be this sorta issue.
Those boards slowly absorb moisture and after time you get a short between pins.
I do recall at least one Aussie Amp tech refusing to work on those amps as it's Marshalls problem but they refuse to recognize they screwed up or something along those lines. Apparently The big M won't cover the cost of repair.
Hope it's not that but thought I'd mention it.
Cheers for that mate, my Marshall is an MA100C and the power valve sockets are actually mounted on the chassis rather than a PCB, the preamp valves are PCB mounted though......
Cool mate, just thought I'd mention it.
Couple of points that have come to light over the years of struggling to get some idea of what is worth pursuing and what ends up cat chase tail.Delta fred
said re valve testers:
"It is something I think of every time I have a piece of valve gear on my bench. Once I have fixed it the desire to build one goes away."
I think there is much wisdom in that line somewhere. nudge wink and I tend to agree.
Unless you are about to embark on running a Valve store house and you need to know every last parameter it's hardly worth the effort.
I'd spend my money on a few extra valves and forget the duds or suspects.
I've noted quite a few comments on valve testers from reputable Valve savvy geeks and the best line was:Best valve tester is a real working Amplifier as Vtesters only give you a hint of the health of the internals.
And this gem from Blackbunny
"OTOH, nobody was making guitar amps with the very high gain structures and inbuilt distortion capabilities
that modern 'shredder' amps have, so maybe older valves had an easier job."
Bingo hole in one.
Interesting also to note that the old RCA books give working HT as say 300Volts for a said Valve yet you measure most modern gear
and it's closer to 400 Volts. And the Valve gets the blame when if runs out of magic puff 6 months later.
Just like motor cars yes you can get 2,000 horsepower out of an engine but it will have to be rebuilt every 440 yards.
An expensive exercise if you just need to go a mile to the shop for a bottle of milk.
A well designed Valve Amp will likely last for years but if you push the limits then expect early failure rates.
My few cents worth,,Carry on.