Mcintosh C22 phono

All NOS Telefunken ECC83 vintage smooth / diamonds in place for about 1 year / 100 hours in a secondary system. Despite little use on phono, the right phono channel is microphonic. Seems all tubes are active at all times. Have done all diagnostics / full service and issue is the tube. Cannot locate a schema or tube layout chart. Am i replacing just one tube or a pair for balance / match  (i.e. Does one tube serve both phono channels)?  All tubes test as new and i like the sound.