Topband: B&W Filament Choke Query

EP Swynar gswynar at
Sat Mar 3 15:17:18 EST 2007

Good Day All,

Mining " olden junque boxxe" here has yielded an undocumented, pre-historic Barker & Williamson type "FC-30" encased filament choke --- I  would be most appreciative if I might solicit some feedback from seasoned, experienced users of this device...

Specifically, the unit has TWO pairs of terminals at EACH END (four per end, grand total of eight). I show continuity between any two terminals only, i.e. any one terminal on the LH side, & its immediate opposite on the other...

Simple & logical enough, with two leads coming into it from a filament transformer, & two leads going out, to the tube's filaments --- but then why the extra four terminals, two per end? Is it because the "FC-30" is, in reality, a "dual" type "FC-15" filament choke, & in order to attain 30-amperes current capability, one must PARALLEL the terminals...?

Also, has anyone ever utilized one of these devices on a frequency band as low as 160-meters...? These things were manufactured back in the day when there was no real practical need of any kilowatt linear amplifiers on Topband, due to day time / night time power restrictions imposed by the old LORAN navigation system. Consequently, I wonder if this thing even has enough inductance on 1.8-MHz to effectively do the job...?

Up until now, ALL of my filament chokes were of the homebrewed variety, i.e. heavy-guage enamelled wire coiled around a ferrite rod...I have no experience whatsoever with this particular pre-manufactured unit, I'm afraid...but I do harbour thoughts of employing it into a dedicated 160-meter-only grounded-grid RF amplifier, utilizing a 4-1000A (still to be acquired!).

Many thanks in advance, & my vy

~73~ Eddy VE3CUI - VE3XZ

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