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MAC 1700 +75V rail?

D

Dave_DC

New Member
I am restoring a early, factory-original MAC 1700, SN 29J24, from 1967. I see that the factory added an RC network to the base circuit of the +75V rail regulator transistor Q39 that is not in the schematic. There is an extra 47 ohm series resistor between C133A and Q39's base, plus an additional 0.22uF "tropical fish" cap directly across Q39's base and emitter leads. I am wondering if versions earlier than mine had any oscillation issues with Q39, and if that is a liability for early models that don't have this network. Or was this mod just to remove any HF noise from getting into the +75 rail? Has anyone ever seen problems with their MAC 1700's +75V rail?

DC
 
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There may be more versions/revisions of the schematic out there. Or it could be a revision during the production run that was not documented.
If you contact the factory with your serial number they will send you a pdf of the schematic for your unit. Also, there may be 'service bulletins' associated with your unit. Be sure to ask about that during your correspondence also.
Good luck and keep us posted.
 
I think that there is an SB for early 1700s, I need to get SBs all scanned in and submitted, ... eventually. ALWAYS search the Hints and Kinks thread in the McIntosh forum though.
 
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