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Hmmm is part of your perfect jam
el34's firing into speakers as well?
Or is the 800 just a master to the Superbass?
I think if it's perfect you run the risk of putting a lot of $$$ into something that will sound different from your perfect sound and even more $$$$ (four dollar signs instead of three) chasing the sound you had in the first place.
I am not sure what your full rig is now and what cabs you're using but I'd use all the $$$$$$$ (that's 7!)
To buy a slave the size of a cab that you can put your 800 on and then have two chassis of tubes one with 6550's the other with 6550's or KT-??
8 or 12 tubes and a built-in vape.

You're fine, obsess about NOS preamp tubes that's a rabbit hole.

I'm loving the mix of el34's in the simms, 6550's in the Sunn and 6l6's in the ward. Maybe what you should do is get a sick kt88 monster slave unit? mod whichever amp you like best to have a slave out if it doesn't already.

i would go strongly with DO NOT MOD!!!

going through your list of intended mods here are my thoughts as a dedicated marshall man.

changing tubes to 6550's- i think this is an acceptable mod. many of them came that way to start with so you are retaining stock characteristics and it won't devalue the amp at all. also, it's interesting to hear both ways. i ended up liking my 2203 with 6550's just a hair more than the one i had with el34's, although i did think the el34 one sounded great. honestly, in a blindfolded test, it'd be hard to tell a difference though. the brand of tubes you use might easily make as big of a difference as the switch to 6550's. but, the mod is cheap, easy, reversible, and doesn't slaughter the awesomeness of the amp, so go for it if you must.

transformers- DON'T! unless you blow one up, there is no good reason to change transformers on these things. those old drake transformers are awesome and are part of the magic in that thing. the best you can do is spend a bunch of money to get new transformers that someone has worked hard to try to make sound as good as the ones you've got. transformers are a weak link in some amps, but not in an old marshall. you will change your tone if you do this, and if it's so close to perfect tone now, why do that?

make it 200 watts- at this point you are butchering the thing. the changes involved in doing this are going to have a huge impact on the sound. on top of that, you're just going to be tearing it to pieces. perhaps resale value isn't that important to you, but no matter how it comes out sound wise, your going to be loosing big time if you do this. it will cost you a ton in parts and labor and the amp will never be worth what a stock 2203 will be. who knows how it'll come out, but if you're not as happy with it as you were before, you'll have a basket case on your hands and you'll never get your money back out of it. all those holes in the chassis and the internal mods needed, i just can't see how it makes sense.

with all the money you'd be into on this thing between the work and the lost value, i can't see how this makes sense. why not just spend that money and get a second 2203 to run with it if you want 200 watts? that's what i did when i wanted more of that amp. and it was awesome. and when i sold one of them, i still profited from the sale. there's also the gear nerd's historical perspective. these things are awesome and they're an important part of our history. unmodded jcm 800's are becoming harder and harder to come by. if you have an old school one that's not been fucked with, then that's kind of a treasure. i think it's a real shame to mod them at this point as a general rule, but particularly if you love it as much as you seem to.

maybe you should look into trying to find a marshall major? i've never played one and they're not real common. i've heard some people don't like them and some do. but it's a 200 watt marshall from that time period. might be up your alley. really though i would just get a second 800. i implore you not to do this project.

a fucking poweramp build! derp why didnt i think of that!?

whiskey_face wrote:a fucking poweramp build! derp why didnt i think of that!?

it's a great idea and seems perfect for you.

*update*

I have a line on one of these locally. perfect.

isn't that a two in one amp? Like the fender 300 that takes 3 cabs?

yup 2 separate 100 watt power amps. HNG

Van it be run in mono to get a 200 watt power amp or stuck with separate 100 watters?

that amp with all the transformers and toobs looks like it could heat up like all hell when push'd.

i reckon that's why it's got a fan. looks awesome, for what the op was looking for.

Chankgeez wrote:If you're happy with the way it sounds now, leave it as is.

Fucking this. Don't hack up a good sounding amp in the hopes you will improve it. And to be honest you will see a bigger change in bass response with a pre amp tube swap than a power tube swap. Tung-Sols and Sovtek wb 12ax7s have the biggest bass response I have found yet in a preamp tube. Chuck one of those into the V1 spot and you'll be good to go. Plus new speakers with a bigger low end response will help as well.

crohny wrote:

Chankgeez wrote:If you're happy with the way it sounds now, leave it as is.

Fucking this. Don't hack up a good sounding amp in the hopes you will improve it. And to be honest you will see a bigger change in bass response with a pre amp tube swap than a power tube swap. Tung-Sols and Sovtek wb 12ax7s have the biggest bass response I have found yet in a preamp tube. Chuck one of those into the V1 spot and you'll be good to go. Plus new speakers with a bigger low end response will help as well.

I have a nos telefunkin in V1 and RCAs in the rest of the pre amp. hnnnng also I use folded horns for 100 hz and down on a separate amp so the 800 doesn't have to have a fuckload of bass response. . .

the only thing im gonna do to the 800 is bias it for 6550s so it and my superbass can run the same NOS ge powertubes. that 9200 HNNNNNNNNNNNNNG must be mine!!!!!!!!1

Sounds like a plan.

whiskey_face wrote:

crohny wrote:

Chankgeez wrote:If you're happy with the way it sounds now, leave it as is.

Fucking this. Don't hack up a good sounding amp in the hopes you will improve it. And to be honest you will see a bigger change in bass response with a pre amp tube swap than a power tube swap. Tung-Sols and Sovtek wb 12ax7s have the biggest bass response I have found yet in a preamp tube. Chuck one of those into the V1 spot and you'll be good to go. Plus new speakers with a bigger low end response will help as well.

I have a nos telefunkin in V1 and RCAs in the rest of the pre amp. hnnnng also I use folded horns for 100 hz and down on a separate amp so the 800 doesn't have to have a fuckload of bass response. . .

the only thing im gonna do to the 800 is bias it for 6550s so it and my superbass can run the same NOS ge powertubes. that 9200 HNNNNNNNNNNNNNG must be mine!!!!!!!!1

The pre amp tube swap isn't going to make it a destroyer of worlds in the lower registers. But it'll add some noticable oomph. I run a Super Lead with 6550s. Suppose to run el34s so I am no stranger to that game. I haven't ran this amp with anything but the 6550s though so I have no idea what the difference in tone and feel is between the tubes in this amp, but this amp is fucking crushing as it is right now.