Topband: B&W FC-30 Filament Choke: EPILOGUE

EP Swynar gswynar at
Sun Mar 4 07:55:59 EST 2007

Good Morning All...

...And many thanks to the SEVEN respondents who took the time to address my query yesterday re. the whys & wherefores of my old Barker & Williamson type "FC-30" filament choke...

For benefit of any interested parties who may one day chance across one of these assemblies at a Hamfest, etc., here's what I learned on the PLUS side (file it away on the back-burner --- it may prove to be useful at some time):

-The FC-30 is, in essence, TWO type FC-15 filament chokes in ONE enclosure;

-Each of these FC-15 chokes is rated at 15-amperes: to safely pass 30-amperes through them, you simply parallel the two, and,

-The unit has the flexibility of feeding two separate tubes from two separate filament transformers via its two separate chokes (maximum 15-amperes per filament, of course), or, one tube / paralleled tubes requiring 30-amperes maximum.

Now, on the MINUS side:

-The FC-30 is specified for operation from 3.5-MHz to 30-MHz, inclusive: because each FC-15 rod is only 3-1/2" long, it does not have enough inductance for 160-meters;

-Even if I elected to SERIES-connect the two interior FC-15's to secure twice the inductance for possible use on Topband, I would be robbing it of its ability to handle 30-amperes of filament current...and my hoped-for 4-1000A requires 21-amperes to make it glow (sigh!).

I've always been curious as to the possible effectiveness of employing the ferrite core from a TV picture tube deflection yoke / coil assembly as the foundation for a robust torroid-type filament choke...I have an inordinately LARGE example of one here, which was removed from a junked early colour TV set many years ago: maybe this is an opportunity in disguise, waiting to be realized...

I have no knowledge of anyone ever having tried this latter trick, but I can't see why it wouldn't work.

~73~ Eddy VE3CUI - VE3XZ

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