For these last seven years, I've been stuffing the HT battery of my Roberts R66 (PP3s are cheaper than new mains smoothing caps you see..) with nine instead of ten and can honestly say that, when I discovered the fact that the Associated Dairies own brand PP3s are larger than GP ones and changed them, the extra battery made no detectable difference to that set's performance.
I'd also need to keep the little chap for a further 62 years at my current rate of usage for the 81V HT supply to be the cheaper long term solution!
