[R-390] OT: Transistor Amplifier Question

[Charles Steinmetz]

Barry wrote:

> On the preamp board, those 50pF caps are across base and collector, not base and emitter.
> On the phono board, some transistors have that across base and emitter while others have that across base and collector.

Caps from base to collector reduce the stage bandwidth much more than 
caps from base to emitter, owing to the Miller effect.

As I said before, the B-E caps were almost certainly intended to 
mitigate RF interference (which Marantz alwys had a problem with, for 
some reason).

The B-C caps were almost certainly added to kill oscillations in the 
phono and line amplifiers (which Marantz solid-state gear also often had 
problems with).  It is possible that the KSC1845s you are using will 
upset this balance, and require some adjustment to the B-C capacitor 
values.  Be sure to check with an oscilloscope when you are done to make 
sure none of the amplifier modules is oscillating.

Best regards,

Charles