mark iii coli, full power/half power question

[Xtravigent]

hi everyone,
so my mark iii simulclass coliseum is in peices on the floor, as I am trying to determine the impact the 'half power/full power' switch, for as far as i can tell, it does NOTHING.

Now I have been doing my reading, and as far as i can tell, there are 3 schools of thought, one - it cuts the outer tubes. this is definatly not the case. 2 - it lowers the screen voltage on all tubes, perhaps, but i sense no change in volume, high or low. 3 - pentode/ triode switch, this is most likely, but again, I notice absolutly no change in tone or volume or anything.

i have checked the switch, it is switching correctly, so not stuck on or off. I usually run a pair of EL34's in the centre, but have tried all 6L6's also, no difference.

I have studied both my circuit board and schematic's for a 100W (im guessing, it has 4 tube sockets, so its not 60W), simul (i realise these will be different) and the position of the switch in the circuit does not match that of the 'class a/simul' switch.

Anyone have any clues, or suggestions of what to look for on the circuit board to identify a pentode/triode switch, or anything else? I would have thought id have heard SOME difference, maybe you can tell me otherwise, this is my first mark iii! Thanks all, Mason

 

[zodiac272]

Hey
I got a IIC+ simul coliseum a month ago so ours are very similar except mime has a limit knob, and different circuits but still similiar. I just posted in another thread in the mark series, that the full/half switch engages another screen resistor to lower the plate voltage to all tubes, therefore all tubes always on, so never class A and always simul. My switch doesn't appear to do anything either, but mike b told me it's working as it should. Mike b also said the simul are about 120 watt full and about 80 watt half and that would account for the switch appearing to do nothing. My limit knob was not working so he will fix that. I'm dying to get it back in another 2 weeks.

Scott

 

[Xtravigent]

good info mate. interesting about the 120W rating, never heard that figure stated! when i pulled it apart, i noticed the resistors were switched onto the four outer tubes, avoiding the centre ones. ill keep digging through it, im gonna attempt to to notate the full colisem power circuit, its pretty hard to come by otherwise!

2 weeks mate, thats a killer! although i had to wait 3 weeks for mine, it arrived while i was overseas, nice rig to come home to!

 

[JOEY B.]

On the Mark III Coliseum simul amps that I had, the voltage to pin #4 of the power tube sockets(outer four) was shut off in half power mode.

 

[Xtravigent]

hey mate, thanks for that. that seems to match up with my limited amp experience showed up when poking around in there.

so is it just the nature of the simulclass circuit that brings its overall power rating down to 150W (or 120W as ive been recently informed!), as compared with a class AB? or is there some way of trying to tweek it up, im guessing with different resistors, to closer to the 180W mark? or am i just going to burn my pride and joy, with me along with it, to the ground?

 

[zodiac272]

I'm sure a resistor change could do what your wanting (more power) and it would seem as though the trannies should be able to handle the extra power, but I dint think it's a good idea. Changing the design parameters without tweaking other things could lead to damage or a not so sweet sounding amp. I can't imagine 120 or 150 watts not being enough. I'd leave it stock
Scott

 

[JOEY B.]

hey mate, thanks for that. that seems to match up with my limited amp experience showed up when poking around in there.

so is it just the nature of the simulclass circuit that brings its overall power rating down to 150W (or 120W as ive been recently informed!), as compared with a class AB? or is there some way of trying to tweek it up, im guessing with different resistors, to closer to the 180W mark? or am i just going to burn my pride and joy, with me along with it, to the ground?

The difference between 120 and 180 watts will not be audible. The triode wiring of the
Siimulclass sockets is the reason for the lower power. Slave it out to a power amp if you need more power, and keep your hands free of the deadly DC voltage. 8)

 

[Xtravigent]

Thanks guys. Yeah, I won't tamper with it, it is a truly unreal amp, in my opinion better than my iic+, which ill be selling now. The reason I ask is I am planning on building my own coli, so I'm trying to understand the nature of its power circuit. Anyone built there own transformers before? Hhahaha

 

[zodiac272]

haha no, but the PT is from the bass 400+. not sure of the OT. oh and I don't doubt that you love your coliseum more, but think hard before selling your IIC+ JMDBO (just my douche bag opinion)

scott

 

[Xtravigent]

yeah, dont worry, ill give it some serious thought, but i have had the iic+ for a while, and honestly everything i get out of the coli i like more that the little 60W. i wont be letting it go cheap, thats for sure.... hahaha. i might move it along to fund the second 4 by 12 for the coli, and this build project