Thanks guys.  Having mulled this over (again) and was thinking, would it be more feasible to use simply 2 of the existing Marshall boards in a bridged design, lowering the output - my thinking is that the heatsink and fan asssemlby would be sufficient for cooling a single IC. 

In terms of sounds, I haven't used the amp in donkey's years, I figured I'd get it working and then look to mod the preamp stage (if I can work out something more akin to a hot rodded JCM 800 I'd be happy - though channel 2 does an almost credible job).

Cheers guys, there's a ton of threads over at music electronics forum on them and how "suspect" the actual design is.  Tbh, the amp was purchased in my youth (depressing when I think of what I could've got for the same money, but hey ho, you live you learn); it's not a bad sounding amp, I figured I try and get it back to working condition. I've been using an old H&H poweramp with a POD XT Live for ages now.

"J M" as you say, the design seem crackers - add to that the floating ground and somethings bound to go belly up on the road.  This had been my thoughts, to shoe horn a fully discrete circuit in there (or even a kit type if that'd be applicable).  If anyone has any suggestions on where I can go with this please feel free to chime on in!

Once again, cheers!

Sunny

** Just a quick one, could I slot something like this off the shelf kit (http://www.velleman.eu/products/view/?country=es&lang=en&id=360242) in without too much fuss?

Hey folks, great forum (I kinda ended up here by chance)!

I have a Marshall Mode Four head thats been sitting in the garage for a couple of years now - the output TDA7293 modules went up in smoke (at a bloody gig just before we were due to go on).

After a load of digging around on the internet, I've learned that this is apparently a common problem with the Mode Four, and that the IC's may go pop anytime even after they have been replaced.  I've disconnected the power stage, and the preamp section and all the functionality works as it should (via the tuner out or FX send).

I've been looking at ways to improve the reliablity of the amp so that I can gig with it in confidence that it won't produce some onstage theatrics of its own!  Is this something worth doing or should I simply replace the 4 IC's and hope it holds out?

I've attached copies of the power amp stage and power modules schematics, thanks in advance!