schematic for 12.6 VDC heaters

[cbutterworth]

I have searched the forum for this, but can only find schematics for 6.3VDC. Also, I do not have ready access to a Windows PC, so no PSUD.

I am thinking of converting my 6.3VAC heated Aikido into a 12.6VDC Aikido. This may help, reduce the remaining small amount of hum, while allowing me the chance to try 12SN7 and 12SX7 tubes besides my current 6SN7. The Broskie PCB has a number of jumpers that can be used to run 6.3V heaters from 12.6V, and I'll install sockets at these locations.

If anyone has a simple diode-rectified circuit, that they could post or describe, I'd be real grateful. Both 12SN7 and 12SX7 take 0.3A current, so the rectified circuit would need to be able to deliver at least 1.2A. The 6SN7 require 1.5A for heater, so it would need to be able to deliver at least 6A, although maybe the current required would be less with 12VDC.

Regards,
Charlie

[cbutterworth]

Sorry....

6SN7' require 0.6A for heaters = 2.4A for 4 tubes.

Charlie

[Eli Duttman]

Charlie,

This is pretty easy. You need 1.2 A. for the "12" V. heater tubes. The power requirement does not change.

Do you already own a 6 A./6.3 VAC filament trafo? If not, buy a Triad VPL12-4000. "Full wave" voltage double the 6.3 VAC using a pair of substantial Schottky diodes. BIG 'lytics are in order for the doubler stack, say 2X 10000 muF./15 WVDC. Follow the doubler with a pair of 7812 3 terminal regulators (1 IC/heater pair). Put a 100 nF. film cap. directly across each regulator's I/P terminals. Put a 4.7 muF./25 WVDC 'lytic directly across each regulator's O/P terminals. Put a parallel combo of a 4.7 muF./25 WVDC 'lytic and a 10 nF. ceramic across each tube's heater, at the socket.

[cbutterworth]

Eli,

Yes, my transformer is rated for 16A, so this circuit should work. I'll figure out the schematic from your description and ask you if it looks OK.

Charlie

[Sheldon]

Originally posted by Eli Duttman
Charlie,

This is pretty easy. You need 1.2 A. for the "12" V. heater tubes. The power requirement does not change.

Do you already own a 6 A./6.3 VAC filament trafo? If not, buy a Triad VPL12-4000. "Full wave" voltage double the 6.3 VAC using a pair of substantial Schottky diodes. BIG 'lytics are in order for the doubler stack, say 2X 10000 muF./15 WVDC. Follow the doubler with a pair of 7812 3 terminal regulators (1 IC/heater pair). Put a 100 nF. film cap. directly across each regulator's I/P terminals. Put a 4.7 muF./25 WVDC 'lytic directly across each regulator's O/P terminals. Put a parallel combo of a 4.7 muF./25 WVDC 'lytic and a 10 nF. ceramic across each tube's heater, at the socket.

This makes sense, but I wonder about the lytic at the socket - not as a practical matter, as it's not much cost to do that. The heater wiring is going to be pretty low in inductance and I would assume that most noise components are back by the power source. I can see the ceramic to dump any stray RF noise, but what kind of noise is the lytic required for, or is it one of those "it's cheap, easy, and can't hurt?

Sheldon

[Eli Duttman]

This makes sense, but I wonder about the lytic at the socket - not as a practical matter, as it's not much cost to do that. The heater wiring is going to be pretty low in inductance and I would assume that most noise components are back by the power source. I can see the ceramic to dump any stray RF noise, but what kind of noise is the lytic required for, or is it one of those "it's cheap, easy, and can't hurt?

Sheldon,

You are correct about the ceramic caps. being noise suppressors. All the other caps. outside the doubler stack improve regulation.

[Valverine]

Does it make sense to also include a choke (as per Lynn Olson note) or it makes a difference only in DHT heater supplies? Or ceramic caps that you mention will serve the same purpose?

Thanks!

[SY]

A common-mode choke can be a useful thing. The normal filtration and regulation is very effective against differential mode noise but is useless for common mode. More simply, you can rely on some small symmetrical resistance and inductance on each leg of the feed (assuming you wired your heater supply in a rational way), then bypass each heater pin to chassis ground with a small ceramic cap.