I wonder if there's a way to turn a 100watt hi-gain dual reverb into a 50watt head? Of course I could get an original 50watt head but I've just located a white (original tolex) head with two matching straight cabs.
JCM900 from 100w to 50w?
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anitoli
Well-Known Member
There is a switch on the back that will change the power tube configuration from 100 to 50 watts:
http://www.drtube.com/schematics/marshall/jcm900.pdf
http://www.drtube.com/schematics/marshall/jcm900.pdf
ampmadscientist
Well-Known Member
It's 42 watts, low power setting is triode.
close enough...
iron broadsword
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Don't do the pull two valves thing, it's not the same and then you have impedance to worry about. The triode switch works pretty good, and I use it most of the time. You're best off with an attenuator though if you are just after more power tube crunch.
ampmadscientist
Well-Known Member
The Broadsword Dude is correct. It's crunchy.
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Ken
Well-Known Member
I would suggest a pedal. I never got a good low volume distortion sound with that amp without one. 50 (or 42) watts is still loud and if you need the power tubes singing without a pedal or attenuator that's the way to go unless you can crank it full up. There is a great 4100 mod thread that you should check out. Some of the clips have me thinking 4100's might actually be salvageable as plug and play amps.
Ken
Ken
Maybe I should clarify me, I don't want low volume. I want the amp to break up earlier. A 50 watt head is loud enough but breaks up "faster" than a 100 watt amp. A 100 watter has so much "loud" in it that it gets ridiculus.
Question is, is there a need to, with a Master Volume amp?
(nope.avi)
Master Volume amps are made for pre-amp distortion, at lower levels.
So your question doesn't make any sense (technically)
If you want powertube distortion with a JCM900, you are killing small rodents....remove plaster from walls and probably beach some whales in the process.
(Master Volume at 7 (in a well isolated rehearsal studio) made the neighbours complain (who were also in a isolated rehearsal studio) on a model 2100 MkIII...)
Ken
Well-Known Member
On this amp, his question makes perfect sense since the DR is decidedly NOT a preamp distortion amp as far as the tubes are concerned. It's all SS (clipping diodes) despite those 4 preamp tubes staring at you. Without mods or pedals, the only way to get a decent overdrive tone is to crank it and get the power tubes in play. This was the main reason I sold mine.
Ken
Ken
Well-Known Member
Oh, I missed that! You can still use an attenuator on that amp, but I'm like you and use the MV on an amp where the distortion is from the preamp. An attenuator on a DSL doesn't make much sense either.
Ken
Rokinroller
Well-Known Member
Even the 100w JCM900 MK3's have the same 100/50w switch in the back. Mine did. But its not THAT much quieter at the 50w setting. Its a different tone just a tad less output volumewise. Don't pull 2 power tubes , its useless and not good.
tschrama
Well-Known Member
Sure you can pull the 2 outer tubes, set the impedance at halve your cabinets impedance. Then set it to low power (triode) mode.
Then discover that 21 watts is still too loud
Then discover that 21 watts is still too loud
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