> how to hook up the heaters and I have found nothing.http://www.lynx.bc.ca/~jc/hum.html
At first glance, heaters are just heaters, you just have to give them power.
The 12A?7 family gives you two heaters that can be fed 12V series or 6V parallel.
BUT: the cheapest source of heater power is raw AC from the transformer. And that is equivalent to a 6V 60Hz tone leaking all over the audio. So heater wiring layout is critical. The link above gives good tips and a photo of a bad job.
Most guitar amps put the audio components either very low on the socket or on a tag-strip, and then the best layout is to bring the twisted heater wires straight-up from the socket. Most pro audio tube layout favors setting the heater wiring in first, pressed hard against the chassis, and wiring the audio circuits high. For a row of tubes, you bring the twisted heater wiring out perpendicular to the row, then bend and run parallel to the row, then bend into the next socket, to keep the heater wiring away from the audio.
Good well-twisted well laid-out AC heaters don't hum.... decades of very clean gear was built this way and very little of it resorted to DC heater power. Bad AC heat will hum bad.