Getting My JCM 800 (2204) Hot Rodded

[gtrjunior]

I’m dropping off my Marshall to a local amp guru, Manny Bettencourt for the hot rod treatment.
I don’t have all of the details yet but should tomorrow evening. I’m giving him the amp tomorrow and we will talk about what we can do with it.
I’m hoping we can
1) add another preamp tube for two more gain stages
2) split the channels and turn this into a proper 2 channel amp.
3) a previous owner added a tube driven fx loop so we may make that the gain staging and opt to add the Merto Zero Loss fx loop.
4)add a ppimv.

I’m kinda excited. Lol

[briman]

I have a 2204 combo version 4104 and it is honestly the best amp i have ever played. It has many mods however. It has effect loop with tube added, Switchable 2 chanels (clean and crunch), a ppv and kt66 tubes with bigger tranny to accommodate them.

The low input jack on front became footswitch jack to change chanels. I will own this amp until i go to my grave.

The mods you are talking about sound same. You will love it.

Paired with g12-65 speakers sounds insanely good. Great speakers.

[gtrjunior]

My amp already has a tube driven fx loop installed by a previous owner.
The amp needs a little
maintenance at this point. Nothing serious, but it still has the original filter caps from 1986!!
I ordered new ones today. And I had the ppimv kit delivered a couple of days ago.
After I drop the amp off tomorrow I’ll post again with the mods we are planning.

[briman]

I think signs that caps need changing is when amp hums alot??

[splawndude]

Or they start to oooze!


Good luck Junior. It would be cool if the modder could take some pics a long the way for you to share.

[gtrjunior]

Nov 2, 2018 20:45:48 GMT -5 briman said:

I think signs that caps need changing is when amp hums alot??

We talked a little about this and I also did some online research.
The “old school” thinking was exactly as you and Splawndude stated. Hum, leaking and swelling are the physical signs of needing new filter caps.
However, the oil inside the cap can dry up and not necessarily exhibit these signs in an obvious way. I saw an article where they opened up an old cap and it was completely powdered inside. The oil had dried up. There were no signs of age or failure on the outside of the cap.
Now, I have read a lot of potential misinformation on the web too...
Some sources say you should change caps every 5-10 years...others say every 20.
Personally, I tend to think sooner is better than later since the cost of a cap is about $10 each.
If a cap goes bad there is a potential for it to take out transformers with it. And that’s not an item you want to be replacing.
My 2204 still has the original Drake transformers and I’d like to keep it that way!!

[gtrjunior]

Nov 2, 2018 22:29:42 GMT -5 splawndude said:

Or they start to oooze!


Good luck Junior. It would be cool if the modder could take some pics a long the way for you to share.

I’ll mention that to him.

[briman]

Hmmmm good to know and thanks for info GTRjunior. I will change all mine next tube change. Or maybe sooner. I'm not sure how old mine are as i just got the amp and it is 35 years old! I know the mods were done 10 years ago and that is about it.

[gtrjunior]

Nov 3, 2018 11:16:05 GMT -5 briman said:

Hmmmm good to know and thanks for info GTRjunior. I will change all mine next tube change. Or maybe sooner. I'm not sure how old mine are as i just got the amp and it is 35 years old! I know the mods were done 10 years ago and that is about it.

The original caps Marshall used were a brand called LCR (I think).
So if that’s not what’s there, they have likely been changed.
F&T is a popular and high quality replacement cap.

[gtrjunior]

I dropped the amp off yesterday and ended up spending about 4 hours just talking and playing guitar with Manny!!
He has a really cool amp that he built for himself that we played through and I also brought my QR and played that too.
So long story short, we decided that we would take the Marshall mods in a few steps.
First thing he will do is replace the filter caps and check the bias. As well as install a PPIMV.
I’m not sure if I mentioned it earlier in this thread but this amp, to me had always had this type of harshness to it. It’s never been quite as smooth sounding as other JCM amps I’ve heard....
He heard the same thing too.
So he is going to look closer at the circuit board to see if maybe there have been some component changes made previously...who knows? Maybe at some point in the past the amp had failed and somebody fixed it but used an incorrect value on some components?

So the next step would be to talk about the gain staging.
A previous owner had installed a tube driven FX loop. I think we might end up using that tube to add two more gain stages to the amp.
I would also order and have the Metro zero loss loop installed in its place.

Finally we discussed turning it into a two channel amp. That would be a bigger job and that’s a bridge we will cross down the road though. I believe the amp would pretty much need to be pulled apart and some big wiring changes would be in order.

One step at a time. My wallet appreciates that. Lol

[briman]

I would leave gain stage and loop tube as is and just use a tube screamer or boss sd1 in front of it. They go together so well.

Les paul + sd-1 or ts9 + 2204 = tone heaven!!

[gtrjunior]

That’s what I’m trying to get away from

[briman]

Oh. On my 4104 that's modded i use the sd1 on the crunch chanel as gain stage is original. The clean chanel is awesome. Hope yours turns out as good. Best clean clean i have ever used. Might have something to do with with kt66's?

My 2203 downstairs sounds awesome too and had a plexi mod. No clean chanel though. I just roll back guitar volume. Nice clean but not as nice as 4104 clean chanel.

[gtrjunior]

Now that I think about it I might ask if it’s a possibility to make the extra gain staging foot switchable.
So, stock...hit the switch and more gain.

[gtrjunior]

Well, I know it’s possible but it depends on how expensive reworking the amp like that will be.