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RE: active loading with parallel feed?

Posted by gluca (A) on February 12, 2011 at 22:31:43

In Reply to: active loading with parallel feed? posted by DanK tubes on February 12, 2011 at 21:59:00:

Dan

you want to use the parafeed calculator (mine or the more complete by voltsecond) to have an idea of what is going on with a CCS. Links to the spreadsheet have been posted here a number of times.

With CCS the limiting factor at low freqs is indeed the primary inductance of the output transformer. Keep in mind that the CCS needs to drop the whole voltage swing of the output tube that is your B+ must be 100s volts higher than the plate voltage and this requires a big heatsink. I'll make an example. Suppose your B+ is usually +300V and suppose you are aiming at 3W into a 5k load, that is 122VRms or 770Vpp, that means your PSU must be 300V+770/2=685V and the CCS must dissipate 17W if you bias the tube at 40mA. Numbers explain that the whole idea is not very practical.

All that said, I have used parafeed OPT and CCS in all my preamps and that is something I strongly suggest every time.

Gianluca

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