Re: Marshall guitar amp schematic /advice please

Actually, you have set it up wrong. Take a line from "send" to another amp. If clean then pre-amp good. Insert a signal to "return" then from speaker jack to speaker cab. If thats distorted then its the power amp section. The speakers do not connect to the output with the "level" pot. In your picture you are running into return then out of the DI/Output which will bypass power amp. The DI is directly after the return jack....

Re: Marshall guitar amp schematic /advice please

Have you tried without the "link"? It shouldn't be in there for normal operation as the jacks are tied together until a cable is inserted. If still having issues, then your diagnosis will be good as the send/return jacks are at the end of pre-amp.

Re: New Members - please post your introductions here

G'day everyone. Guitar junky from Sydney, Australia. I work mainly on guitar gear.
Looking forward to adding any info I can to this forum.
Cheers