12 Volt DC Heaters

[Gingertube]

Some of the HiFi guys use an alternate scheme to regulating the supply for all the heaters.
What they do is use an LM317 with a small heatsink configured as a current regulator, one for each tube. That has an additional advantage in that it provides a "slow" start for the tube. You don't get that high current surge into a cold heater.
This may be worth trying.
Cheers,
Ian

[mooreamps]

s

Some of the HiFi guys use an alternate scheme to regulating the supply for all the heaters.
What they do is use an LM317 with a small heatsink configured as a current regulator, one for each tube. That has an additional advantage in that it provides a "slow" start for the tube. You don't get that high current surge into a cold heater.
This may be worth trying.
Cheers,
Ian

I would recommend constant voltage verses constant current. Say If someone wants to pull a power tube or a couple of power tubes, then the voltage rises up out of the regulator to maintain that current load over the rest of the tubes. Now you're looking at a cascade failure....

-g

[Gingertube]

Gary,
You are quite right - thats why in my post I said "one for each tube". That is one current source per tube, they can all operate of the same power supply.
Cheers,
Ian

[tedmich]

my 0.02

-three terminal voltage reg chips are one of the few places where tant caps are the correct choice, at least according to the guys who design them, just get the polarity right and maybe use one of the newer, "nonsplody" polymer based electrode ones.
-a VR bringing 24vdc down to 12v requires a large heatsink and will get very hot; best to get as close as possible to the VDO and not dump so much to IR^2
-running a tad low on the DC voltage can increase tube life quite a bit; I believe Merlin supports this practice.
-people who do A/B testing often find DC heaters are not worth it with MANY high gain designs using other toplogies; AC series, elevated, hum cancel etc etc

[jpfamps]

-running a tad low on the DC voltage can increase tube life quite a bit; I believe Merlin supports this practice.

The only data I've seen on this is a graph in Audio Cyclopedia showing that valve life is compromised by both too high and too low filament voltages.

If I use DC heaters (which is rarely) I use a 3 terminal regulator and run the filaments at 12.6 VDC, ie as specified by the data sheets.

[tedmich]

Merlin has suggested a lower "standby" heater voltage, see the bottom of this page:
The Valve Wizard

also see A/3 from this page:
http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm

also see here:
http://www.diyhifi.org/forums/viewtopic.php?f=4&t=1604

NOS Telefuken ECC803S? maybe run the heater voltage a bit low....

[trobbins]

Specification for most valves is +/-10%, so a regulated 5.7V to 6.9V per heater is quite acceptable. The +/-10% tolerance can also be used to allow mains variations for unregulated heaters supplies - although in many situations local mains is very much tighter.

[mooreamps]

Perhaps the A/C line voltage is better regulated at 240 volts down under, than in this country at 120 volts.
-g

[trobbins]

Well it's not too variable in suburbia where I am :-) I also don't have much in-house voltage drop induced variation. But I should put a recorder on the mains one day, and then repeat during summer when everyone turns on air-conditioning during the day :-(

[Tage]

Thanks for all the replies, I've worked out a circuit and am just waiting on some parts to test it out, I'll post here on how it goes.