You do know that the Dynaco SCA-80Q is a SOLID STATE amp and this is the Dynaco TUBE Audio Forum ? We don't really deal with any of the Dynaco solid state amps on this forum - BUT - C9-C11 are part of the main power supply for this amp. If one one of those caps were to be bad then it would affect BOTH channels. On that amp there is a PC-17 board and a PC-18 board for EACH channel. More than likely one part on one of the boards has gone down. The early Dynaco solid state gear was (unfortunately) not very reliable and the "loss of one channel" is THE most common problem found on the early Dynaco SS gear.
Although neither Roy Mottram or myself deal with Dynaco SS gear, you may want to try this web site > Update My Dynaco web site. They sell parts for Dynaco solid state gear. They may be able to help you. We do have a complete assembly manual on file for the SCA-80Q at the link below ..
Dynaco SCA-80Q assembly manual