[Collins] RF Choke ID

[Dr. Gerald N. Johnson]

On Mon, 2008-04-28 at 12:54 -0400, bill riches wrote:
> I found a NOS Collins  Ceramic Plate RF choke that I am trying to identify:
> 
> Total Height 5 9/16
> 
> ¾ diameter
> 
> 1 7/16 x ½ mounting flange with 2  6-32 mounting holes drilled from the
> bottom of the flange.
> 
> Coil wire has green insulation and measures 37.5 uH. The number 540-7979 was
> written in pencil on the bottom.
> 
That would be a Collins fab part number. Google turned up a reference to
a federal stock number 5950-00-772-8399 but the only hit for either
http://www.tpub.com/content/logistics/59/50/282/00-772-8399.htm didn't
really describe the part or show usage. Its too tall for a 32S or KWM-2.
Maybe it would fit a 30S-1, though my schematic doesn't show the
inductance of its plate feed choke and my 30L-1 schematic shows its was
44 uh.

Its ID is complicated by the fact that every PA needs one. Its reactance
is about 400 ohms at 1.8 MHz which looks low for 160 meters. Or a PA
that goes down to 2 MHz. 850 ohms at 3.5 MHz might work in a PA with a
low plate load Z. But the RF choke will run hot.

The apparent inductance will be affected by the frequency of measurement
because of the distributed capacitance of the winding. Without an RX
meter to measure its parallel properties, it can be checked with a grid
dip meter. Resonances found with the terminals open are high impedance,
good frequencies for use. Resonances found with the terminals shorted
are series resonances and frequencies where it should not be used.

It sounds as if it has considerable insulation between the mounting
flange and the lower terminal so can operate at a few KV plate voltage.
You can check the wire size and probably figure at least 500 circular
mils per amp of plate current (high current density for a multilayer
winding, dependent on cooling of a single layer winding).
> 
> Any info on this choke would be appreciated.

If there are no series resonances between 3 and 30 MHz, I'd guess its
for a Collins 1 or 2 KW linear covering that range, else if there series
resonances outside ham bands (excluding WARC bands), I'd guess 30S-1.
There is some chance it was used in several power amplifiers, maybe even
for a grid choke in a higher power PA.
> 
I don't know of Collins supplying plate RF chokes as a commodity item
though they did that for toroids.
> 
> 73,
> 
> Bill Riches, WA2DVU
> 
> Cape May, NJ
> 

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer