by Ty_Bower » Sat Jul 04, 2009 5:10 am
Shannon posted the pdf for IRCL specs here:
http://www.diytube.com/phpBB2/viewtopic ... ircl#14684
You want to size the thing based on the expected Steady State Current (amps). Then you're looking for a high resistance at cold (25 deg C) and a small resistance at "Under Load at % of Max Rated Current".
The CL-90 is designed for a 2 amp draw. It is 120 ohms cold, and goes down to less than 2 ohms at 75% of load. The tricky part is figuring out the current draw at the power transformer. I usually screw up the math here somewhere. What is it for a single Mark III? Say it's about 440VAC @ 150 mA, plus 5V @ 2A, plus 6.3V @ ~4.15A. That's a whopping total of just over 100 VA. There's going to be some efficiency losses in the power transformer - let's pretend it is 65% efficient? Then we need somewhere in the neighborhood of 150 VA going into the power transformer. At a line voltage of 120 VAC, we would need about 1.25 amps going into the primary winding.
Multiply that by two for a pair of Mark III, and I'd guess that a single CL-90 won't have the necessary current rating. Putting them in series won't work either, since all the current would need to go through each one. You might get away with wiring them parallel to each other, but I don't know how they're going to split the load since their resistances are going to vary as they heat up. You'd probably be best going to a CL-80 for its higher max current rating.
Find someone to check my math. I probably made a wrong assumption in there somewhere.
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