Looking for 6.3V 1A ccs heater supply for dht

[martyh]

Can someone please point me to a schematic that would be suitable for use with a 6.3V 5A transformer?

Thanks,
Marty

 

[revintage]

Hi Marty,
Unfortunately a CCS normally needs a little more voltage to work properly. A CCS-connected LM1084/1085 does IRL need 11V DC(bridge +10000u). So a 9V winding is what you need. We have found this to work great with 6B4G.

 

[Circlotron]

Why would you want to use a ccs and therefore have the filament voltage indeterminate. Why would that be better than a fixed, regulated voltage source?

 

[Fuling]

According to "common knowledge", constant current sounds better than constant voltage. I believe it has something to to with isolating the filament (which is a part of the signal chain) from the filament PSU. Half science, half voodoo I guess.

In the latest version of my 6B4G SET I use LCLCL-filtered filament supplies. The last "L" is an huge 112mH iron cored choke that serves the same purpose as an active CCS. Works very well!

 

[Circlotron]

Hi Fuling.
Do you still have your choke-loaded source follower class A amp? Mine is still going strong after all these years.

 

[Fuling]

Hi Circlo!

Unfortunately the answer is no, I never got it just right so I abandoned the project years ago. Some of those chokes are in my 6B4G filament PSU right now

Back to topic, here´s a voltage controlled current source (VCCS) that I find interesting:
http://techgraphix.bodewits.com/PDF/Electronisch/FilamentSupply.pdf

I have plans for using a beefed-up version of this circuit to feed a pair of 813 (10V @ 5A each)

 

[Tweeker]

Why would you want to use a ccs and therefore have the filament voltage indeterminate. Why would that be better than a fixed, regulated voltage source?

CCS also gives a soft start (this is possible with voltage sources too, but takes more parts) helping extend cathode life. Turning on a filament is the hardest thing you can do it it, damage being proportional to the cube of the inrush current. Ohms law takes care of the rest, heat being a function of current.

It would be possible to use a 6.3V 5A winding to provide 6.3VDC 1A CCS with a voltage doubler rectifier arrangement. Wasteful in terms of heat and capacitors, but well within the transformers capability.

 

[dsavitsk]

this might get you started http://www.diyaudio.com/forums/showthread.php?s=&threadid=142095&highlight=

 

[Tweeker]

Use a pair of Schottky diodes. Most other parts were picked from Apexjr, dropping resistors 1.5R 10w, capacitors axial 3,300uF 35V. Heatsinked lm317. Resistor on Vout pin is 1.2R 2W.

 

[martyh]

Thanks to all for the help.

I like the simplicity of the chip regulators. Thanks tweeker for taking the time to draw a schematic. I recall doing one with LM317s (sans voltage doubler) a few years ago for a 201A filament supply and I had some trouble getting the correct voltage across one of the tubes. Anyone know of suitable pot for using in the current set position that would allow me a bit of adjustment?
Thanks again,
Marty