Re: 1976 100 watt Marshall JMP Super lead vs 1977 JMP Super lead.
As far as this cascading/non-cascading, here's my attempt to explain it (if I'm wrong let me know). Vintage Marshalls use a 12ax7 for the gain stage, as most of you know, but for those who may not, a 12ax7 is a dual triode meaning it's two triode tube circuits in one tube bottle. So to explain how these work in these amps I'll compare it to something else guitar players are familiar with, the humbucker. Like the triodes in a 12ax7, a humbucker is two individual coils in one pickup that can be wired a variety of ways. Non-Master Volume amps are wired to use one side of the tube for each channel, like wiring up the bucker to run split. If you wanted more gain you could jumper the inputs with a patch cable and use both gain stages at the same time in parallel, just like with the pickup, it increases output (gain), but the character remains similar to using a single input. Cascading preamp run the halves of the tube in series for maximum output, this is what the Master Volume amps use (except for the first year or two of the 2204). As the amp the OP is talking about is modded it may or may not have a cascading preamp, or may be able to run either way depending on what input you plug into. Ask the seller as many questions about it as you can think of, but IMO you should buy it, worst case scenario is you end up not liking it after a while and you can sell it for what you bought it for
As far as this cascading/non-cascading, here's my attempt to explain it (if I'm wrong let me know). Vintage Marshalls use a 12ax7 for the gain stage, as most of you know, but for those who may not, a 12ax7 is a dual triode meaning it's two triode tube circuits in one tube bottle. So to explain how these work in these amps I'll compare it to something else guitar players are familiar with, the humbucker. Like the triodes in a 12ax7, a humbucker is two individual coils in one pickup that can be wired a variety of ways. Non-Master Volume amps are wired to use one side of the tube for each channel, like wiring up the bucker to run split. If you wanted more gain you could jumper the inputs with a patch cable and use both gain stages at the same time in parallel, just like with the pickup, it increases output (gain), but the character remains similar to using a single input. Cascading preamp run the halves of the tube in series for maximum output, this is what the Master Volume amps use (except for the first year or two of the 2204). As the amp the OP is talking about is modded it may or may not have a cascading preamp, or may be able to run either way depending on what input you plug into. Ask the seller as many questions about it as you can think of, but IMO you should buy it, worst case scenario is you end up not liking it after a while and you can sell it for what you bought it for
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