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Re: McIntosh C2200 premap

RE. MC75, over the years I have worked on a number of these and actually use the MI75s ( same thing but rack mount and higher voltage on the output tubes). The first thing you should do is check all voltages against the schematic with the amp at idle. The voltages should be very close to what is printed. The power supply voltages must be correct first then check the output tube pins and work back through the small tubes. The power supply uses 4 large caps two of which are voltage doublers. These are available at Audio Classics for the doublers, and various sources including Antique Radio Supply in AZ for the 500V 100/100 mfd.
If a voltage is off you can substitute a different tube. With no change look for a bad cap or resistor. I usually just shotgun all of the small caps for modern film types. Orange Drops from Antique Radio supply are fine for little money. Pay attention on the few resistors that must be matched. Carfully measure the ones in the amp and if in doubt replace them. Pay attention to the feedback network as the amp will work when this is off but will lack clarity.
I know some will say keep the original parts in the amp but it will be more stable with new caps and the noise floor will also improve.
As for tubes every one has an opinion. The 12at7 that drives the outputs should be stout like a five star 6201 GE. The input 12ax7a will alter the sound of the amp from soft to sharp. What you use kind of depends on your speakers. Stick to the original schematic and you will end up with an amp that sound as good or better than the day it was made. If the voltages are correct and the tubes are good the amp will meet spec.
Ron-C


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  • Re: McIntosh C2200 premap - Ron-C-McIntosh 03/23/0209:50:31 03/23/02 (0)


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