How do you put a CCS under a diff. pair of DHTs???

[andyjevans]

For some reason I don't remember seeing any schematics for a diff pair of DHTs with a CCS. My balanced line stage already uses a diff pair of 1626 with a Morgan Jones type CCS (as in his book, p.134). So how do I deal with the filaments of a DHT? I've never used DHTs but I need to know so I can try out some 26s in the first instance, then one or two other DHTs. Can somebody talk me through this (schematics very welcome) for:
a) AC filaments
b) DC filaments - probably necessary with a 26

Thanks for your help here! I don't know if this is simple or difficult - never seen it done. Andy

 

[dhaen]

AC:
Cross-connect the heaters in parallel to cancel hum. Connect CCS to centre tap of FLOATING heater transformer winding.

DC:
Parallel heaters, cross-connected is better to reduce effects of ripple. Connect CCS to negative of FLOATING DC heater supply.

Edit: Added FLOATING to AC case.

 

[dhaen]

AC:

 

[dhaen]

DC:

 

[andyjevans]

Thanks, John, that's very helpful. With the aid of some D cells I might be able to get my 26s up and running to see what they sound like. Andy

 

[Rocky]

You probably know about Gary Pimm, if not google him up. He has some good info on implementing CCS's in various circuits, push-pull included, in his article "CCS's and signal current control".