Marshall Artiste project - will this work?!

[Jennings]

I've recently got hold of a 70s Marshall 2x12 Artiste (Model 2040) combo in very poor cosmetic shape.  Baffle board's shot, split and crumbling and needs replacing (see my thread in the cabs/speakers section...many of the screws are rusted and reamed on the head so I'm having trouble getting the baffle off at the mo!).  The chassis has a LOT of dirt and some rust patches from what looks to be moisture and spills.

Basically I'm going to start by taking all the of the board, caps, sockets and trannies off the chassis and giving it all a good but careful clean up.  Probably do the chassis with some steel wool and then coat or varnish it after...that a good idea?  Then I'll look to reinstall the iron (after I've cleaned that up as best I can too...I'll just gently rub the surface blems off and maybe do a rust passivation or a varnish to protect).

However...I'm aware the 2040 circuit isn't liked by all.  I'm going to give it a try as-is just in case I'm bucking this trend.  but I wanted to get some ideas on possible cool mods to try.  I was thinking maybe of doing one preamp channel as a bassman or tweed type Fender, and the other channel as either a selmer TnB mk2 or a Marshall plexi type.  Maybe leaving the power section as-is (it's essentially supposed to be the same as a Marshall 50w Bass amp).  What do folks reckon?

[sluckey]

I'd fix the amp electronically just as it is before tearing it down to clean it. Evaluate it and go from there.

[Jennings]

Probably a good idea...although with this level of rusty fixings, rubbish, dirt, broken solder joints etc I figured I might as well assume I'll have to strip and clean anyway.  Amp was sold to me as working, and the board looks fairly stock, bar a couple of replaced resistors over caps and a new (but also old) mains tranny.  I'm intending to put it back together as stock after the clean, make sure it all runs then, and subsequently do any modding.  Was interested in what people might come up with while I was doing the clean and initial reconstruction.  There's that whole reverb set up to play with...I'm not a big user of reverb (so none of my other amps have it), although I wouldn't mind tweaking the one here be as good as I can get it, therefore giving me the option should I fancy it.

[Jennings]

Update:

Well I changed the filter caps and gave the amp a visual once over before firing it up to test it.  Sadly I got a moment's sound and a couple of slightly distorted sounding cords out of the amp before it all went quiet.  I tried cleaning jacks and checking leads etc and repeating the test, and except for the occasional split second of sound at the start there's nothing.  More often or not I just get nothing.  I'm not even getting any hiss from the speakers, so presumed a connection had either broken or maybe had cracked solder etc somewhere in the output.  Especially as the amp worked for a split second, but now doesn't even hiss when on.

Wondering whether it was as simple as a bad connection from the OT to the speaker jack, I wired the OT leads from the impedance selector directly to a fresh brand new jack and tried again.  Not a sausage, so it's not that.  

So that's where it is currently...until I find the fault.  Currenly I haven't had time to take voltages, try and check/reflow joints, check components etc, so I have all that to do.  I'm hoping it's not the OT itself that's gone...I've had that before where the amp for a split second might make a tiny proper sound and then nothing which turned out to be a blown OT.

How do I measure an OT to see whether it's OK?  Never actually done it myself, so I'm unsure as to where I put my meter probes!  Good lesson...don't plan ahead until you have the amp working in its original state!  Haha!!!

[Ritchie200]

How's it going with the rehab?  I would first pull voltages and post them here before you invested too much time on the OP TX.

Once you get it up and running, you can do the old Fender trick of jumpering out the reverb tank and wahla, you have some grind.  You could also cascade the two channels, but that would take a lot of work.  You may want to keep it as original as possible.  Any old oddball Marshall will bring $$$ in operating condition.

Good luck!
Jim

[Jennings]

I put it to one side this last week or so really while fixing up a little old chap style amp I had laying about (it used a 6V6, 6SL7GT but with a 6X5GT rectifier)...

...tonight I shall have another look at the Artiste.  Might be able to get a couple of photos as well as some voltage readings.  I'll certianly try to post the voltage readings on here in the next day or two.  Determined to get this one back to life.  I've got the cabinet repairs on the go, so I really need to sort the amp out soon!  I'm hoping it's as simple as dirt in the valve sockets or duff socket connections!  We'll see...watch this space!!!

[Jennings]

Well after a bit of time last night I managed to get the voltage table below.  The bits that look immediately wrong are pins 6 and 8 on V3.  This is the reverb driver valve, isn't it?  I don't have the reverb connected at the mo...would that cause this or does it indicate a problem?

Anyhow, I have some good news too...After a bit of fiddling I have got the first channel to of the amp to work fine.  Turns out I'll have to replace the octal sockets as the valves I originally had in there didn't make enough contact with the knackered (tarnished and slightly bent/damaged...this amp's been about the block!) conductors in the sockets...I eventually got it going by some wiggling and the use of a set of EL34 with fatter pins!  The first channel with just Bass, Treble and Volume controls worked OK.  Presence control worked OK too.  Wasn't the most exciting amp tone...but then I was running through an attenuator into a 10" Jensen alnico.  Might be lacking a bit of bite and sparkle.

However when I plugged into the second channel with the reverb, I get nothing at all...not even any hiss as I turn the volume up on that channel.  As I said before, I don't have the reverb module connected at the mo (I don't know whether that makes a difference?!).

Good news is that the worst case scenario of needing a new OT is avoided  

[sluckey]

However when I plugged into the second channel with the reverb, I get nothing at all...not even any hiss as I turn the volume up on that channel.

Most likely something wrong with V2 circuit.

No voltage on V3 pin 6??? Check the 100K plate resistor indicated on the pic.

[Jennings]

Thanks Sluckey...I only had a few mins last night, but in that time I did find that the V3 100k plate resistor wasn't passing any voltage, so replaced it.  Haven't yet had time to fire the amp up to see what difference that made, or check the full V2 circuit, but I'll try to give it a go in the next day or so.

With regards the channel that is working (which has bass, treble and vol controls), what are the best simple changes I can do to get a slightly more exciting sound out of it?  Should I live with it as-is, or should I totally modify it?  I'll wait to get the rest of the amp working, and try the chassis out with a few speaker types before I commit to any alterations though.  Should have my new baffle arriving shortly for the cabinet...the original one was water damaged and split beyond saving.

[Jennings]

Well, I eventually got both preamp stages of the knackered Artiste running...the issue with the second was a wire chopped/trapped  by one of the turret board fixing lugs.  However I'm still keen on making some changes to give me an interesting amp more suited to my needs.  Especially as this one with all its cosmetic damage, dents, tears and rust is not worth much on the collector's market.

I'd like to use the first channel for an AC30 inspired preamp (using the first set of 2 inputs, Vol, Treb & Bass controls).  The second channel I'd like to make fairly Marshall-like by using a JTM50 approach.  The output section I won't touch, so it'll be left as similar to the standard Marshall 50w bass that the Artiste already has.

For ease I referenced three Ceriatone layout diagrams (I'm still not great with circuit diagrams I'm afraid!) for the three amps I'm hoping to combine...see attached.

Am I right that I have enough valves in the Artiste to make my hybrid?  And would it be as simple as joining the output of both preamp stages I build into the PI via the 0.022uF cap the Treble controls feed into, leaving the PI unaltered?!  Or would I have to have some kind of mix network first?!  

[Tone Junkie]

I like to combine channels too, what i find when combining two differant types is the worst thing that happens is one channel is louder than the other .
sometimes can be over come by the volume knob other times have to put a resister in.
 Bill

[Jennings]

Thanks Bill...that's very handy to know.  Glad I'm on the right track then.  Out of interest, what sort of range resister values do you  find yourself using when combining channels?

I have another question too...is it wise to use two halves of one ECC83 for the inputs of both preamp channels, or does it not really matter?

[Jennings]

OK, I've used a bit of free software to draw my layout (attached - in part!).  Two propblems with this...firstly, it's a bit messy so sorry for that...secondly the software doesn't seem to have coped too well with the size of my layout and list of materials.  It's cut the left and right off the diagram, and stopped adding things like the resistors in the component list at about resister 35 etc.  I have printed the B.O.M. separately though.

Hopefully people can get the idea of what I'm doing though...does it look like it'll work?  Does the circuit look like it'll work...or where have I gone wrong?

The output valves are EL34s, and the four preamp valves are ECC83.

Cheers,

Jennings.


PS: If anyone knowns where I can get hold of some better software for drawing my layouts, I'd be very grateful...obviously things like VISIO would be good, but I'm not sure I can justofy forking out for a powerful tool like that at this stage!

[Jennings]

Doesn't seem to be much interest from the forum....in the meantime I'm having a go at drawing my first ever circuit diagram based on the rubbish layout I cobbled together.  I'll post it when I'm done...I'm trying CircuitMaker Student, so we'll see how I get on with that!

[sluckey]

Not much to be said about an incomplete layout. We really need a complete layout PLUS a schematic. Then we can compare the two to see if they agree. Did you keep to the original schematic?

BTW, Visio can be purchased with a huge discount if you can get a teacher or student to get it for you.

[Jennings]

Thanks for the VISIO tip...I'll have to tap up some of my old uni friends in the teaching world and see what they can do for me!  Especially as right now I have a trial version of SmartDraw, a student version of CircuitMaker, and a couple of versions of the DIY Layout Creator software.

I was just meaning there weren't many people interested in suggesting possible build options, or answering many of my questions.  It's probably not the most interesting project to the on-looker, but for me it's turned from getting a VERY tatty old basket-case amp running to actually becomming a very interesting build/mod...and I'm getting much better at reading schematics as a result!

The layout's not great (although the main board is in the pic), but hopefully I can get the circuit diagram drawn to make the complete idea that I currently have make more sense (I'll post back with than when I'm done).  It's taking a little time though as I'm having to combine the font end of the Vox type and JMP50 type circuits with the 50w Bass PI and output section...and learn how to draw/read schematics at the same time    Not to mention find some free software and learn to use it before I can upgrade to something better.

[jbefumo]

Yeah, old threat, I know, but ... wow -- jumpering the reverb tank -- what a great idea.  Never even thunk of that.  Hmm -- maybe with a relay and foot switch? Have to cogitate on this.  I typically like less or no reverb when running OD, so could be a perfect low-impact mod ...

How's it going with the rehab?  I would first pull voltages and post them here before you invested too much time on the OP TX.

Once you get it up and running, you can do the old Fender trick of jumpering out the reverb tank and wahla, you have some grind.  You could also cascade the two channels, but that would take a lot of work.  You may want to keep it as original as possible.  Any old oddball Marshall will bring $$$ in operating condition.

Good luck!
Jim