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Surgery Time! (JTM45 Modding Content) : Amps

Surgery Time! (JTM45 Modding Content)

For amp builders.

Surgery Time! (JTM45 Modding Content)

Postby RitchiesPartyHat » Wed Nov 29, 2017 9:16 pm

So the story goes...

- Back in 2002 I purchased a bone-stock, used Marshall JTM45RI for about $600.00
- It sounded like arse and was nothing like a mid 60's JTM45
- In 2004 I installed a PTP kit and lots of fixin's (MM OT, NOS Mullard pre's, VA KT66 power, etc)
- It sounded great!

Fast forward to 2013...

- I wanted MOAR GAIN and the ability to use 6CA7s, so I modded it again
- swapped grid resistors from 470 to 1K
- swapped 27K NFB resistor to 47K
- moved NFB wire from 16ohm tap to 4ohm tap
- tried a 500pf bright cap but yuck... took it off (100pf stayed)
- got a pair of EHX 6CA7s... very nice - clank and crunch
- it sounded closer to what I wanted...

Here's what it sounded like (and currently sounds like):



So fast forward to 2017...

It's time to finish the job. The amp is still extremely thick and needs to have some more parts changed
to get things exact. I also gotta figure out something to go from shared cathode to split (turret board
is designed for shared only).

I've gone through the amp and labeled everything (huge size, so had to shrink it; probably unreadable).

IMG_5223 - Values-1024.jpg

My ever-faithful assistant is ready to lend a hand...
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Re: Surgery Time! (JTM45 Modding Content)

Postby RitchiesPartyHat » Mon Dec 18, 2017 3:00 am

Done! I'll post a pic of the guts later.

Meanwhile, here's a quick clip in honor of the dude (BPJ) whose '66 JTM45 Bass first inspired me to get into building/modding Marshalls
way back in the early 2k's on the Plexi Palace forum:



Signal chain:

2008 Gibson Custom Shop '61 LP/SG Custom (57 Classics)
|
amp (everything dimed except bass "1", vol "9")
|
1x12 w/ Celestion Alnico Gold
|
SM57 hair off-center of cap
|
UA 2-610
|
DAW

- No EQ except hi and lo pass
- Waves iR1 w/ Sunset Studios echo chamber (just a touch)
- For wah, I had to use VST (BIAS FX) and manually move the virtual treadle with the mouse
- Izotope Ozone 7 on the 2
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Re: Surgery Time! (JTM45 Modding Content)

Postby RitchiesPartyHat » Thu Dec 21, 2017 5:04 am

after pic:

IMG_5301 -1024.jpg
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Re: Surgery Time! (JTM45 Modding Content)

Postby IAmTheWalrus » Wed Jan 17, 2018 6:31 pm

Sounds damn good!

:D
Farmin' ain't easy...
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