Yes, I had read somewhere about this constantly applied biasing.
As far as I can tell, SSB doesn't seem to be affected and seems to stay constant, so it seems to be a carrier fault.
Copies of the service and user manual found on the 'net below, plus a couple of pictures of the actual set in question.
Actually, I've just found that the two manuals are too large to upload, but they're out there somewhere on the 'net, so I'll try to find where I found them originally.
Edit: This looks like it:-
http://www.radiomanual.info/schemi/Y...T-950_serv.pdf