Just completed first amp build - JTM50 clone (mostly)

[CalGTR]

I'm not new to DIY electronics, but this is the first amp build I've attempted. Pieced together a schematic from different places, and built it using valvestorm JMP50 chassis and board. Sourced parts from various places, including a bunch from valvestorm. I found their service to be fantastic, quite frankly. Just a great resource. Transformers are Marstran, with a 1202-118 power transformer and 784-128 output transformer. The green resistors are Kiwame carbon film. There are a few AB carbon comp and a couple metal film sprinkled in. No great plan or scheme for which resisters I used where - pretty much just used what was handy, although the default was to use the Kiwame carbon film resistors.

The workmanship on my part isn't as immaculate as some of the amp build you see around here (I'm sure I'd be able to improve this aspect a bunch on my next build), but not too bad. The amp sounds pretty darn amazing, and I'm sure I'll be tweaking things further as I go along. The cathode bypass cap on V1 is 33uF, and I might even try going a bit smaller yet. Sounds good as-is, though. The amp might be a bit too squishy overall for me with the current rectification and filtering, so might try solid state rectification and/or additional filtering at some point. Anyway, here's the amp as it is currently constituted:







Anyway, it was a fun process to put this together, and I'm sure I'll build more.

[coldengray]

Nice work! Very neat for a first build, congrats on sourcing the parts yourself. Where are you located?

[CalGTR]

Nice work! Very neat for a first build, congrats on sourcing the parts yourself. Where are you located?

Thanks. It was a fun part of the process to source the parts. I'm not sure I would have enjoyed it as much if everything had been put together in a kit. Not having a kit allowed me to customize a bit. However, Valvestorm sure makes things easier by providing hard-to-source parts (chassis, faceplates, and so forth). I'm located in New Hampshire.

[coldengray]

I agree, sourcing the parts is half the fun. What is planned for your next build? I say keep this one true to original specs and build a JMP50 or JTM45 next, whichever tone is calling you.

[CalGTR]

I agree, sourcing the parts is half the fun. What is planned for your next build? I say keep this one true to original specs and build a JMP50 or JTM45 next, whichever tone is calling you.

Yep, I'll very likely go for a JMP50 of some flavor. I like the idea of keeping this current amp at JTM50 specs (or close to it), and building a new JMP50. We'll see. I could opt to tweak the current amp towards a JMP50 if I wanted to. I deliberately chose the chassis and board I did to be able to move towards a JMP50 if I wasn't completely satisfied with the JTM50. About the only thing that would prevent me from going all the way to a JMP50 is the output transformer. But, the current amp sounds pretty darn great, so might as well keep it pretty much as-is and start another project. I'm also going to need to build a fender-flavor something-or-other at some point, but building these fire-breathing Marshall clones is just too much fun!

[coldengray]

JMP50 sounds like a great idea, especially if you're thinking of modding this one to more lead specs tone.

I have 2 more JTM45s up next, to test different OTs. Then a JMP50 build.

[CalGTR]

JMP50 sounds like a great idea, especially if you're thinking of modding this one to more lead specs tone.

I have 2 more JTM45s up next, to test different OTs. Then a JMP50 build.

Sounds like fun. What I may end up doing is installing a switch or two to go between a shared-cathode, JTM45-type tone stack to a split-cathode, JMP50 lead-type tone stack. Would be pretty darn versatile. Wouldn't want to ruin the great JTM50 stuff going on, but if I can easily add a more JMP50 lead-type mode (although with the 784-128 output transformer, it wouldn't be a true JMP50 lead-type amp), it might be fun. Don't really like the idea of drilling another hole in the chassis, but that's no big deal. I figure if I use shielded cable to run back and forth to/from the switch(es), I can keep noise down. All of this is probably contingent on whether I opt for the solid-state rectification. If I stay with the tube rectifier and lighter filtering, I'll probably not add the lead-type mode. In that case, I'd start planning an entire new amplifier. Would likely be a few months before I could start a new amp in earnest, though.