JTM45 / 1959SLP / 1987 differences

[odysplob]

I've been thinking...

I am in a position to buy a handwired JTM45 at a reasonable price, although it's not exactly what I'm looking for at the moment, in stock format.

... But I'm not opposed to projects. What, internally, separates the JTM from the two mentioned JMP's? I could drop a SS rectifier (or maybe go the extra mile and make it switchable from tube to SS, Mesa style ) in place of the tube, but what would I really need to do to covert the JTM to super lead or 1987 specs and get a similar tone?

Cap changes? Filtering?

ANY help at all is welcome

 

[V2a]

I don't have all the specs fresh in my mind, but there were some differences in power tubes (KT66 vs. EL34) and OT primary impedance (8k vs 3.4k or something).

Lots of component value differences too. All sound good; it's just a matter of preference.

Have a look at the documents on the TubeDepot JTM45+ kit, which uses EL34s and has a Tube/SS rectifier switch. The component values are more along the lines of a JTM50 or the JMPs you mentioned.

 

[PatF]

Is it a late model Marshall or a kit build? Layout wise it should be the same with an exception on the both sides of the board. And like V2a said several variations in parts values that would just require a resitor or cap swap. But at least there are turrets to solder to. You have to find a place for a ss rectifier on the mains side of the board. You could just plug in the Yellow Jackets YJR instead of a tube....?

https://www.yellowjacketstc.com/yellow_jacket/yjr

On the input side of the board there is a shared cathode on V1 that needs a turret added to split. Or you could mount the 68K grid loads directly to the V1 socket and run shielded wire over to them, making room for the additional cathode resistor and bypass cap. A lot of mud can be taken away in just this one area.

You also have the option of doing the JCM800 2204 v1 configuration, or just a cascade one-wire type mod.

Get it running good just like it is then start swapping things one area at a time. Plugging in and playing each for a while. and work your way across the board. The filtering on a 45 calls for 16uf caps which might sound cool, but the later amps used larger values like the 50/50uf dual cans. Swap them out one at a time. A lower value in one spot like the phase inverter might yield something you like.

Check your output tube socket wiring and transformer specs before throwing in EL34's. Heater current ratings etc. I think you'll be just fine sticking with KT77 or 6L6GC.