Marshall superlead plexi 100 watt

[Lee stav]

Hi i wonder if anyone can help me understand the problem with my plexi its very old made in 1969 i had it serviced and nothing changed only the mains transformer which i got from TAD germany i also got the bias tool from them so i could set my own bias when changing valves, which i recently did but using the tool i could only read three tubes in the bias, although one isnt readable it was still lit up so maybe this is normal or maybe not, has anyone got any ideas on this please? cheers Lee

[pdf64]

Maybe the screen grid resistor for that tube has burnt out. Best to query this with the guy that serviced it.

[Lee stav]

Marshall sp100

Hi thanks for your reply, i am concerned playing the amp as i love the tone, as not to damage it and the guy who did the work has retired and i wonder if this is a job i could do myself, i am now listening for any defects to the amp in detail like i was playing and i could have sworn it reduced its power the after a while got slightly louder but the change was so subtle i might have been imagining it, now i am thinking is it related to the valve or is this a different problem so i wish i new about these thing i am pretty determined to learn though ,

cheers Lee

[pdf64]

Try swapping the problem tube into a different socket to see if the problem follows the tube or stays with the socket.

[Chuck H]

It could simply be dirty tube sockets.

[Lee stav]

marshall sp100

Thanks Guys i am in the process of going through the bias testing today again and i will post back my results here later

thanks again Lee