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In Reply to: Re: I used to think that posted by dave slagle on May 1, 2007 at 17:47:52:
For the 71As I used a pair of existing chokes which were about 1H and had about the right DCR to drop nominal 6.3V to 5V. I added a common mode toroidal which tops up the DCR.For the 211s I bought some big transformers off the shelf, unstacked it, unwound the primary and added a new winding. The winding roughly matches the DCR of the existing secondary to give me almost 0.8 ohms as required to drop nominal 12.6 to 10V with the 3.25A draw of the 211 filament. I will add an air gap with paper between the Es and Is and put it on the DCR bridge to see what I get and use the same trick with the common mode toroidals as above.
I have only just sorted the recharging for the 211 batteries so they haven't been installed yet. I'm using laptop power supplies (15V) and a silicon bridge rectifier to achieve 13.8V, the laptop supplies are current limited at 6A so this should work a treat for the 65 Ah batteries.
Follow Ups:
I'm curious, being as you're using DC on the filaments, why aren't you using SS devices for isolation? This seems like a very inconvenient application for chokes given the frequencies and currents involved. I should probably add that I'm on the outside of the current rage for SS CCSs, but this particular use would seem much less likely to color the sound. The impedance ratio of desired to undesired signal paths would be extremely high with a SS CCS.
The original circuits used fairly high spec SS devices (LT108X series regs). With the 71As I moved from there to series / shunt regulation using discrete devices, from there to SLA batteries and from there to SLA batteries plus chokes. I felt that each step was a worthwhile improvement. With the 211s I'm in the process of jumping straight from first to last.I tried SS current reg but didn't like it, YMMV etc etc.
I tried SS current reg but didn't like itYou probably have some theory about the reason why. No?
I never tried batteries, probably should give them a go.
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