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1977 marshall 2104

 
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jonah65
Guitar God


Joined: 16 Oct 2010
Posts: 463
Location: weymouth, uk

PostPosted: Thu May 30, 2013 2:17 pm    Post subject: 1977 marshall 2104 Reply with quote

spluttered and died on me, after a year with no problems.
any ideas?
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ampmaker
Guitar God


Joined: 15 Oct 2010
Posts: 113
Location: Cambridge, England

PostPosted: Thu May 30, 2013 2:39 pm    Post subject: Reply with quote

Any number of things, at this point.

Died how? Fuse popped? Only low level of guitar signal output? Any hum from the speakers at all?

Good thing is - as long as the transformers are still OK - a 2104 can be fixed for not much money.

'77 means it has a PCB, so it's not quite as easy to work on as pre-'73 Marshalls, but it's still a helluvalot easier than working on a modern amp with mixed high voltage/low voltage/digital circuits.
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jonah65
Guitar God


Joined: 16 Oct 2010
Posts: 463
Location: weymouth, uk

PostPosted: Thu May 30, 2013 3:44 pm    Post subject: Reply with quote

hi ampmaker, i'll try and answer with what i know,
mains fuse and ht fuse both ok, red power light on.
no output at all, no hum from speakers.
basically, i switched on tonight as usual, waited about a minute before
switching standby switch on, but it didn't make any sound, then it worked
for about 3 seconds and stopped again, it did this again after wriggling the
different connection leads on a zoom g2 box, then died again.
switched it off and took the amp out of the combo cabinet to see if the valves were glowing, and found two ax7 preamp valves not glowing.
put two spare valves in, and these glowed (all 5 valves glowing).
still absolutely no sound/hum from speakers.
thanks for your interest, any ideas?
cheers, jonah.
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jonah65
Guitar God


Joined: 16 Oct 2010
Posts: 463
Location: weymouth, uk

PostPosted: Sat Jun 01, 2013 1:53 am    Post subject: Reply with quote

eureka! after swapping all the pre amp valves out with no joy, thought i would change the power valves, swapped v4 for an old tesla, and bingo
amp sprang back into life!
just goes to show, even though a valve is glowing doesn't mean it is actually
working.
well chuffed,jonah.
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