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marshall 100watt JCM super PA restoration


umph
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recently aquired this amp with the intention of doing it up and it arrived yesterday and it looked in not such a great state, but i did some quick fixes and it lives! Although it is sounding very poorly, so think its time to bust out the multimeter and replace all the components that've gone out of spec, afterall the amp is from 1974.

heres a few pictures i took today more will follow

someone had attempted to jumper together ALL the inputs via piano wire or something along those lines



close up of piano wire spaghetti



i replaced this and put it back to spec



someone has also put a IEC in but decided that if it was covered in insulation tape it didn't need screwing in (tape not shown)



Heres a whole shot of the board - fairly neat and good quality craftsman ship on a production amp, something you don't see on amps nowadays!



More pictures to come of the full amp and detailing what else needed replacing, guessing most of electrolytics are dead and the power valves are also nackered and need replacing.

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Right had another bash at it today, but got it fully up and running and it sounds absolutely mint! Not sure whether to keep this or my superbass now, the superbass has the lemmy factor but the super pa has the better tone hmm.

First i noticed one of the caps had given up the ghost and had spewed its guts so that was first to be replaced, also the 100k resistor on the cathode follower plate had been replaced with a 150k at some point, so i replaced that aswell.



close up of the cap



new caps



chassis top with old caps



new ones



another shot for good measure



Everything else seems fine at the moment, all that needs doing now is a new indicator light and to drill some holes for the IEC.

will take some more pictures of it in the case when its all done!

Edited by umph
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[quote name='umph' post='937616' date='Aug 26 2010, 10:22 PM']by the way, i really enjoy this sort of stuff so if anyone has any old valve amps knocking about they'd like restoring etc or would like to sell i'd happily take it off you.[/quote]

How much do you think it would cost to replace the output transformer in my amp? It's a 60w peavey tube amp if that helps.

Edited by EdwardHimself
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[quote name='EdwardHimself' post='938357' date='Aug 27 2010, 07:07 PM']How much do you think it would cost to replace the output transformer in my amp? It's a 60w peavey tube amp if that helps.[/quote]
about 50quid i think, transformers are fairly cheap if you don't mind me sticking a marshall one in instead, fairly sure they're similar specs.

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[quote name='umph' post='938472' date='Aug 27 2010, 10:13 PM']about 50quid i think, transformers are fairly cheap if you don't mind me sticking a marshall one in instead, fairly sure they're similar specs.[/quote]

Ok well i don't know if it's the transformer itself that is the problem or it's just not got any juice but it's not buzzing either way so i think the reason it's not working has something to do with that. I think we're off down to sheffield on the next weekend so i'll see if i can take it down then.

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[quote name='EdwardHimself' post='938756' date='Aug 28 2010, 01:36 PM']Ok well i don't know if it's the transformer itself that is the problem or it's just not got any juice but it's not buzzing either way so i think the reason it's not working has something to do with that. I think we're off down to sheffield on the next weekend so i'll see if i can take it down then.[/quote]

Ahh normally isn't the transformer they're fairly robust and only break when they dont have a load on the secondarys, but yes best way to sort it would be to let me have a look.

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