DC heaters

[proaudioguy]

What does it take to build an AB763 with DC heaters?  Can all the normal transformers be used and just use the heater winding and rectify and smooth it?  Seems like that would be really easy if that is the case.  Is there a particular scheme for grounding that? Just ground the negative side?  Which tube pins get the grounded connection?  Can the grounded tube pins be soldered directly to the chassis at that point and you just run the positive 6V DC?  Do you use a voltage regulator?  I would imagine that would be a good idea.  Do the tube heaters draw the same current with DC as they do with AC?

[thetragichero]

no to most of these
check out the bit on dc heaters at the bottom: http://www.valvewizard.co.uk/heater.html

[Bieworm]

Why would one apply DC on heaters for an AB763 circuit? If it's to eliminate hum the root of the problem should be addressed. Or is there high gain circuitry involved?

[SnickSound]

I built a few amps with Dual Rectifier level of gains without using DC heaters and there is zero hum, perhaps a little hiss but that has nothing to do with DC vs AC heaters and is to be expected with 4 gain stages followed by an FX loop.

I just DC elevate the heater reference, to 70-80V usually. This also makes life easier for Cathode Follower tubes, which is not an issue with an AB763 so just 20-30V there would be sufficient. A simple voltage divider of the B+ rail (I tend to do it post choke so it's cleaner), with a 10uF or so cap to ground and that's it.

Oh and I don't even twist the wires either. Just run them parallel. SLO style.

If an AB763 hums, it's probably not because of the heaters honestly. There is probably another reason..