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DO NOT DO THIS ON MAC AMPS !

Posted by Michael Samra (D) on July 3, 2016 at 18:49:40

In Reply to: Full-wave C- Supply posted by Lee of Omaha on July 3, 2016 at 16:48:19:

I have done this on several Citation 2s and I like the sound very much but in the case of the Mc240 and other Mac amps,we have a different situation.Mcintosh uses a bias tracking system and it works in conjunction with the power transformer primary and secondary meaning,when the voltage goes up or down,the proportionality of the bias goes up or down to maintain the correct bias.You always set the bias on a Mac amp with a variac and a voltmeter.On an Mc240,you set the variac to run the B+ 440vdc on the plate and minus 47 on G1. If you don't have minus 47,you adjust the bias resistor up or down until you get minus 47 at 440v.This way when you plug it back into a normal AC wall voltage,the amp will track perfectly regardless of where the voltage moves.
What I do on Mc240s is exactly what McShane did on the Citation 1 and the Citation 5..You put in the 820uf doublers and than dual 100ufs down stream,along with a pair of dual 50uf paralled in for added decoupling capacitance..Then add a bussbar and bolt right on to the choke bolts..I also use Schottky diodes but the GI diodes are fine. The other thing I do is add a hash filter that Eli came up with and that gives you an even quieter background.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

Edits: 07/03/16 07/03/16

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