List of JTM 45 mods you can make

[Big Mike]

alot of these mods are great if you want more of the later lead sound. personally, I prefer other amps for that than the 45. but that's why I have to keep so many amps

Agreed. I just find I'll use the later voicing more for what I do.
So I'm going the other way...a lower wattage modded marshall tone.

It's fun, and I can always put it back.

[Big Mike]

Well I went nuts.

Mustard .0068 for the V1B instead of .022
.018 mustards for the phase inverter plates instead of .01
100pf fizz cap
changed the grid resistors and put some Nos Tesla's from tramp in it.
Split the cathode and put a .068/2k7, and instead of a straight 820, we have a .068/820 like a JMP at the V2A cathode capacitor.

Plus it's internal cascade (See 1 wire mod done easy thread).

I'm pretty happy with it! Left stock JTM45 filtering and tone stack. boat of GE/JAN 12ax7's in the preamp.

[Holgar]

+1 on arledgsc's advice to the negative feedback.
I have tried many mods on my 45er. IMHO the most useful one was connecting the feedback wire to the 4 Ohm tap. I still use the 27k; so my setup is compareable to 47k at 8 Ohm, what is used in the 50 watter. Takes 5 minutes, is for free and opens up the amp in a very nice way.

[arledgsc]

+1 on arledgsc's advice to the negative feedback.

I have been busy trying all kinds of mods since my last post. Besides the 100K NFB resistor my next favorite mod is to lower the PI coupling caps from 0.1uF to .039uF in my case. This helps reduce blocking distortion and smooths out breakup. This one really makes a big difference.

I have also changed the tone stack components slightly to in an attempt to tame the bass response. I have succeeded and my ear likes it. Instead of the bass turned all the way down as before it now sits on 3 - 4. We're talking about a dB or so of less bass so nothing drastic but I now have some range on the bass control.

I finished a JTM50 Black Flag this weekend. Used many of the same mods on it as my JTM45. Sounds really good straight away and I love the grind of EL34s. I think I am done tweaking the components for a while as I am quite satisfied. If I can ever afford NOS tubes then I will try some of them.

Scott

[Holgar]

Hi Scotty, my amp is very similar to yours.
I use 0.033uF PI caps and a 220uF input cap, swapped the feedback cable and changed the mixer resistors to 470k. The rest are original specs, but in the past I put some old mustard and dogbone caps in.
It is hard to find a 270pf cap on a fleamarket! Like the needle in the haystack
I love this amp.

[Roe]

theres an original jtm45 at the plexipalace now with 40uf on the mains. also it may have 16uf on the screens and 32uf on the PI, although this seems somewhat unclear