Apologies "43096". That is what I meant to say. Thanks for pointing it out.
We were on a Birmingham-Hastings ADEX way back then, with the usual roarer to Mitre Bridge, for the Crompton to Eastbourne where they backed the 73/0 on. The weather was pretty miserable and overcast so the young driver switched the ETH on while the ED was burbling away waiting the tip. Got the road, driver took power and the burbling ceased. Someone from the front coach legged it up to the cab and suggested the driver switched the ETH off, and off we went.
There was a similar issue on a tour to the Severn Valley many many years ago which involved a "JA" (73/0) and a "KB" (33/1) in mult. Fine so long as ETH wasn't selected.
So yes, a 73/0 can heat on diesel when static. I am not an expert but I imagine the control and power supply system could be converted from 73/0 to 73/1 standard, but as "43096" says, expecting that much from a 73 on diesel is optimistic to say the least. Has the BB been fitted out with energy saving lighting ? The heat and on board catering would still suck a far amount out of the 73's meagre supply.