by paart » Wed Dec 16, 2015 10:08 pm
Hmmm… I guess I’m no longer getting automatic notifications of posts---and it’s been awhile since I’ve looked at this one.
Yes, an LM7805 regulator will work, if you are using tubes with 5 volt heaters. If not, then an LM7812 or even an LM7824 may be a better choice. These of course, will give you close to 12 and 24 volts respectively. 6 volts is difficult to achieve with a fixed regulator. The LM7812 voltage output, if used as a stand alone regulator will be very close to 12 volts, not 12.6 volts. If 12.6 volts is desired, then a simple 1N4004 diode can be placed between the ADJ terminal and ground. The voltage drop across the diode junction will bias the regulator an additional .5 -.8 volts above ground.
This works pretty well for a tube or a combination of tubes with heaters drawing up to little less than one amp. Above that, a pass device is needed, which complicates the circuit some and adds expense and reduces efficiency, sometimes significantly. An adjustable regulator may be a better choice here, since there is additional voltage drop across the junction of the pass device.
The circuit that I showed is best suited for applications drawing a couple of amps or so. Below that, fixed regulator chips may be quite adequate, assuming that a rectified and filtered DC voltage is available.