JCM800 clone w/ mods!

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.

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

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

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).

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.

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...

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.

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...

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

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.

Haven't had much of a chance to do anything with this project lately due to the kids and wife sharing their germs with me.

However, this evening I DID manage to do the turret board ready to mount all the components. Its not as straight as I had hoped, as it turns out permanent marker pen doesn't actually stick to PTFE board.

Hopefully the plan for tomorrow/this week will be to mount the components to the board and start fixing the hardware to the chassis. I've decided to just leave the chassis as is, instead of trying to paint it.

Not trying to be mean or anything, but your turret board looks like a Friday night after the pub special.... certainly has character that shouldn't affect the sound...

The amp looks cool so far, I'm interested in checking out the demo once it's posted, feel free check out my DIY Valve amp head thread and add comments if you like.

I'm going to be building the circuitry on a Turret Board too, since I've always wanted to try making a Turret Board, my amp is going to be a 50 watt Soldano SLO style amp.

Sorry for the delayed reply, my family seem to have been passing around the same flu and sickness bug for weeks now!

Unfortunately Marcel, I am more practical than pretty.

In the short time I've been well, I have been well, I have managed to mount all the hardware to the chassis.

DrNomis_44, that sounds like a good project! I do love the Soldano SLO amps. Have you visited http://www.slocloneforums.com, there is a wealth of information and friendly people on there.

LOL.... Yeah, I'm with you on that.... my best at pretty isn't always that pretty.... main thing is always 'so long as it works', and it's super nice if it works well...

Quote:

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Originally Posted by Ik7

Sorry for the delayed reply, my family seem to have been passing around the same flu and sickness bug for weeks now!

Unfortunately Marcel, I am more practical than pretty.

In the short time I've been well, I have been well, I have managed to mount all the hardware to the chassis.

DrNomis_44, that sounds like a good project! I do love the Soldano SLO amps. Have you visited http://www.slocloneforums.com, there is a wealth of information and friendly people on there.

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Yep, been to the Sloclone forum quite a few times, I think I even signed-up as a member too, that's where I got the schematics pdfs from that I'm using in my Sloclone 50 build, i did manage to make some more progress on it, basically fit some new beefier toggle switches, Led indicators, 1/4 inch sockets, and black pointer knobs to the chassis, oh and a new 1MA (Log) pot as well, next year I'll sort out ordering all the components and stuff I need to start building all the internal circuitry.


Update:

Turns out I am indeed a member of the Sloclone forum, I just sorted out my login details so I could login again as I had forgotten my last password, anyway it's all good, I might see if there are any new and updated Sloclone schematics and layouts available.

My Sloclone 50 amp isn't exactly what you'd call a work of art either, if I was able to I'd make some changes to the chassis layout so that it balances better when the amp is being carried by it's handle (not attached to the wooden cabinet at the moment).


Here's what it's currently looking like so far:

Attachment 23688

Quote:

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Originally Posted by Marcel

LOL.... Yeah, I'm with you on that.... my best at pretty isn't always that pretty.... main thing is always 'so long as it works', and it's super nice if it works well...

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Wee bit of fibbing going in there Marcel. ;PI submit your collective build works as evidence in contrast to your statement.

Quote:

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Originally Posted by FrankenWashie

Wee bit of fibbing going in there Marcel. ;PI submit your collective build works as evidence in contrast to your statement.

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All I'll say is 'Photos lie.!!'... All too often what is in a photo doesn't always match the reality. Then again maybe I have that talent at hiding the faults through a photograph...

Dr_Nomis, I love the plexiglass front of you amp. Home made definitely has more character...and people can tell when Ive made them!!

I've decided on a Jensen C12R for the speaker to go in the combo. I'm not really a fan of the Vintage 30 or Greenbacks...which is weird when I'm the right side of the pond!

Quote:

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Originally Posted by Ik7

Dr_Nomis, I love the plexiglass front of you amp. Home made definitely has more character...and people can tell when Ive made them!!

I've decided on a Jensen C12R for the speaker to go in the combo. I'm not really a fan of the Vintage 30 or Greenbacks...which is weird when I'm the right side of the pond!

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That's actually a piece of clear perspex I found in amongst the stuff in my dad's workshop, it was lucky that it happened to be just wide enough to fit, all I had to do was cut it to length and drill some holes for the mounting screws, and then fit some suitable pieces of wood scrap to the cabinet.

Part of the fun of making home-made guitar amps is searching for suitable material to build the amp, most of the bits and pieces I scrounged while working in my dad's workshop, I did have to buy one expensive item though, which is the output transformer, if my memory serves me right I think it cost me something like $380.00, or thereabouts, and then when it came to the power transformer I didn't know where I could buy a suitable one, so I found a power transformer that came out of an old reel-to-reel tape recorder, it looked like it was about the right size, so I proceeded to strip it right down to the cardboard bobbin, next I measured the dimensions of the transformer's core, and then did some calculations using a book called "Build Your Own Coils And Transformers", and then re-wound both the primary and secondary windings of the transformer according to my calculations, the transformer actually worked first go.

This time round, I'm going to go ahead and buy a proper, commercially made power transformer.

Yep... Without the proper machinery the whole winding transformers thing is a mugs game... and these days after many barely passable attempts I'd much rather pay someone who has the right materials and machines to do it, and let them do it right...

Funnily enough I bought a transformer book from Australia on how to wind your own power, output and choke transformers. One day I'll have the nads to wind my own transformers, so I commend you on that!

I had an idea for using perspex and drilling a couple of small holes on the end and putting LEDs in to get a nice back glow.

I am loving toroidal transformers at the moment, if I could find an output one for the right price I'd use it.

Many many many many many moons ago, when toroidal transformers first came on the market, a few intrepid builders tried making toroidal output transformers... and although they are better at efficiency and they cost about the same to wind, the whole idea never really took off as the 'puritans' amongst us complained that they "don't sound right"...

Technically it makes sense... at 50Hz or 60Hz the current make up of the ferric former of the toroid is ideal, but the same former for wideband audio use is not as it has different responses at different frequencies... find the right former with a ferric (or some other) make up that gives an acoustically appealing response and you'll be on a winner.... There are dozens of former types to choose from... Good Luck !!

I actually had to re-wind the transformer all by hand, to say that it was tedious is an understatement, the very first time I re-wound it I ended up having to completely strip it down to the bare bobbin and start again because when I put the laminations back in I accidentally cut one of the primary windings with one of the laminations, eventually I succeeded and had a working power transformer.


Because a Toroidal transformer has a core shaped like a ring, the magnetic field is shaped differently compared to a conventional transformer, the magnetic field is more contained, the benefits of that is lower induced hum-noise.