RCA BC-3c console losing low end

[natrecstudio]

Hi,

My BC-3c is passing clean signal on all channels, and the Audition bus (which is only available via the built in  power amp) sounds great, but the Program bus (which is the output to the real world) sounds dramatically thinner than the source signal even though the associated board's voltages were checked, and that board (as well as virtually everything else) has been recapped.

The line inputs were at some point modded with UTC transformers and Daven trimpots internally, but the behavior is the same on the mic channels, and as I say, everything sounds correct on the Audition bus, so I'm not suspecting this is an issue.

I would so appreciate any input as to what you'd consider first in trying to track this down..... so close, and yet so far!

Thanks!!
Danny

 

[ruffrecords]

The first thing I would suspect is the negative feedback from the tertiary winding of the output transformer or the feedback resistor on the 5AR8 board (2R12) or the connections between them. The unusual thing about the program amp design is it uses a pair of paralleled push pull 12AU7 tubes. If one of these was faulty then the transformer impedance match would be wrong which could lead to a thin sound. Try changing these tubes?

Cheers

Ian

 

[emrr]

Isolate and check the PGM amp by itself.  Second Ian's thoughts.  As well can be bad switching in that path.  listen/test signal at various switch points too.