[bob orbell]

OK Graham, it looks like you have omitted, or fitted the small round black insulator from the regulator chip's heat sink upside down, the larger part should be upper most, the regulator heat sink must be compleatly insulated electrically from the chassis, and it should be quite tight to allow heat transfer, also, not relevant to to the heater problem, but all the large resistors should be well clear of the PCB because they will get quite hot and damage the board, do run over your soldering again with the iron and some flux to remove the blobs and allow the solder to run in the joint's, you are not using enough flux, do not just rely on the flux in the solder. To check the regulator before you start, see if the is any resistance between the earth post and the regulator heat sink, as I have said there should be open circuit. BOB