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Re: [TCML] DC charging choke.

Hi Charles,

You have a high-power DC resonant charging reactor (or choke) most likely from a fairly large stationary or marine radar system. Bendix was a major manufacturer of radar equipment during, and after, the 2nd World War. Resonant charging reactors are part of a "line-type modulators". The charging reactor efficiently (re)charges the pulse forming network (PFN - a combination of inductors and capacitors that was designed to mimic a charged length of HV transmission line). The charged PFN is discharged into the primary of a step-down pulse transformer, using a spark gap or thyratron switch.

The PFN and pulse transformer create a relatively square-shaped high-power pulse, typically several microseconds in duration, that powers an RF power oscillator tube (a magnetron or klystron). The power oscillator generates an approximately square-envelope pulse of microwave energy that is piped and transmitted through a highly-directional antenna to echo-locate distant objects.

For more information, Google "Pulse Forming Network" or "Line Type Modulator". The high-current rating of your reactor would allow it to be used with a relatively large storage capacitor in a DC coil. The choke can handle a 0.1 uF tank capacitor, allowing you to handle ~25 kW of power at maximum break rate of about 480 PPS. Very nice find!

Radar charging chokes appear to be relatively rare at Ham Fests or Teslathons. Over the last 25 years, I've only seen one. They tend to be real boat anchors - heavy, oil-filled metal-cased, with large asymmetrical insulators (a smaller Vdc input insulator and a larger 2X Vdc output insulator). For example, here is the one I have:


The above oil-filled charging reactor is rated at 67.2H, 122 mA, 15 kV in, 30 kV out, at 192 Hz (or a maximum of 384 PPS). It weighs about 75 pounds. It was designed to be used with a PFN having a total line-ground capacitance of ~0.01 uF at 15 kV, delivering a bang size of about 4.5 joules. Unfortunately, the maximum power (at maximum PPS) for a DC TC using this reactor would only be about 1700 watts.

Hope this helped and best wishes,


charles rakes wrote:
I'm using a Bendix choke on my dc Tesla coil, that has the following
ratings, 4.8H,  5 ohms,  2 amps dc and a 17KV working voltage rating with a
max of 35Kv .  I'm guessing its weight at near 100 lbs or more.   I've had
the choke for over 20 years and was wondering if anyone might know what
it's original use might have been?  Are there anymore out there?  tnx,
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