JCM800 clone w/ mods!

[Ik7]

While I am waiting for my custom order to arrive from Pitbull, in the mean time I am going to build (another) JCM800 style amp.



Its based on the JCM800 with a couple of changes; VOX AC styled phase inverter stage with no presence control, slightly more gain from the second stage, 30W output with a quad of JJ 6V6S tubes and fianlly the preamp tubes are all Russian ECC83 equivalents.

The new amp I am going to build will be an 18W combo, with more mids (more SLO-ish), choice of either EL84 or 6V6 tubes (all Russian), more gain from the second stage, ultra-linear or normal modes and finally a Jensen C12R speaker is the drug of choice.

As soon as the parts start arriving I shall start updating pictures and hopefully by the end I shall have sound clips.

[Marcel]

Interesting combination of tubes and circuits... Any particular reasons for your choices?

[Ik7]

I've gone for the JCM800 just because its pretty easy to modify and change without getting complicated. I use Russian tubes because they can usually take higher voltages and are a bit more ruggered.

I like the sound of the 6V6's on break-up, they are like a smoother version of an EL34. However, with this amp I really want to see what EL84's can do, as the only experience with an EL84 was in a SEL AC4

[Marcel]

Your current amp looked interesting, but cant see it now that you have changed the link...

Remember to post lots of photos as you build your kit in a build diary and here on this thread for your amp. (I use the paperclip attach in the 'Go advanced' menu).

[Ik7]

That's a better idea, rather than trying to use failbucket (I'm sure it never used to be that bad).

I'm really looking forward to my kit coming, nervous in case I bugger it up, but hopefully it will turn out playable.

As soon as I start more of the amp (hopefully the next couple of days) I will upload some pictures of the build process. I can't decide what do do with the chassis though, I had an idea of dropping it in the sea and leaving it outside for a few days to get it to start to rust, then cover it in lacquer to preserve it; so a sort of "rat" look...or just leave it bare metal. As you can see from my previous build...I do like the "rustic" look.

[Marcel]

Once rust starts it is very difficult to control, and more often than not it will gravitate to places you really prefer it didn't go.

I have a 2204 build made from a chassis from the '70's. It had a lot of surface rust which was easy enough to clean off with sandpaper and seal with some hammered metal finish spray can paint, however there is one spot of real aggressive rust under the power transformer mounts that refuses to be arrested and will see to the demise of the chassis in only a few years if I don't stay on top of it.

I'd suggest not coating the parts you can see once it is built and coat properly everything else. A little natural surface corrosion will build up soon enough...

[Ik7]

So today I managed to clean, fold and start drilling the holes in the chassis. There has got to be an easier way to put 28mm holes in mild steel! Still can't decide on what finish, if any to go with.

Tomorrows task is to position the power transformer and choke, however I'm still waiting on my audio transformer from Italy.

[Marcel]

To get those larger holes I use a step-drill made by Cabac. Available and most good plumber or electrical wholesalers. Only problem is the need for a 13mm or 1/2" chuck on the hand drill to make the buggar turn...

[dave.king1]

+1 for step drills I have a few in different sizes ( and a bloody big drill press )

[Ik7]

I used a 20mm Armeg holesaw, then a 6-30mm step drill bit to widen it. Where I work, we have a full workshop, but the drill press doesn't have a very big chuck, so i'm limited to anything with a max core of 10mm.

I'm still waiting for little bits and bobs to arrive, but when it does, I shall start taking more pics and getting on with this build.