I can't locate any notes with details of the power transformer. The transformer itself may have ratings - take a look!
I do sort of recall that there was not enough heater current available to make a DC heater supply. I know this was true of the Foreplay 1, and I believe it was also true of the FP 2. People were trying separate wall-wart type DC supplies for this reason. The last version (3) used the much larger PT-3 in order to have plenty of heater current reserve, and it came stock with the DC heaters.