Marshall IBS 6040

[craigmillard]

Hi Guys,

I have just got hold of one of these bass slave power amps 200w 2 channel:) Thinking of using as a poweramp for my last build, a x88r.

Anyways its not working at the moment and wanted to ask a few Q's from the fountain of knowledge!

Its a mosfet based amp with two of these sections in it:
http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/marshallamps/bass_200w_3520.pdf

Im going to debug it when i get home later but just wanted to ask some basic Q's

1. Do i need to have a load connected when powering on with mosfet amps? can i just turn it on with no speakers attached?
2. Its a whopping 200w and unfortunately i dont have a cab that can handle that at the moment (soon though ) is it ok to run into a lower wattage cab but with the preamp volume turned down? As this is a slave amp it doesnt have a volume..
3. The mosfets all look ok but how can i tell? none look particularly burnt out..

Cheers all
C

[duck_arse]

I don't think you need a load with mosfet amps. you can run it into a smaller cab, with the levels down, but don't drive it into clipping or you will get smokes.

as for the mosfets, I have a set of 4 unused Hitachis sitting around here (soon going to eebay again). I tested them by puting them into a breadboard booster circuit. let me know if you want them.

[craigmillard]

Nice one duck_arse!:)

Thats what i expected, just this amp doesnt have a volume on it so if i just use my preamp volume that will set the output wattage?
Also if no input does that mean no output wattage?
Just dont wanna fry my vintage 30's lol

Cool whats the numbers on them? this amp uses 2sk134, 2sj49's..

[craigmillard]

Just an update on this in case anyone else come by..

The cause of the fuse blowing was a failed rectifier on one side of the amp, replaced with a heavier duty one and all is gravy now!

This beast is loud!!