If they are DC then my amp tech found a way of extracting a supply to run a fan to cool the heatsink. Not sure when i'll get chance (maybe at the weekend) but I'll take some photos of the insides so we can work out how he did it.
You could email Nik and ask?
Unfortunately, DC-30's, like most vintage-amp based designs, uses AC heater current.
Modern amps, especially high gain ones, rectify the heater current for DC use in the preamp, it's a lot quieter and in an amp with high compression, the noise floor matters a lot more.