The AM Forum

Good evening.

Can anyone identify this RF choke manufactured by National? I have looked at older publications and catalogs without success. It measured 100 uH, DCR 2 ohms. Looks like it is parasitic free for both series and anti resonances. So a nice choke. Is it pre the R175A series or after? There is a 500 pF 20 kV decoupling cap at the base which will need replaced, appears with a small crack. The p/n off the base of the choke reads GA-1404C. Thanks in advance, Alan

  Looks like the plate choke used in the ART-13 transmitter

 Bob W8LXJ

Sure does Bob. Thanks. So should be good for a single 813 and probably 500 mA.
Alan

Looks Collins to my eye??

old handbook around 1953, it is a national choke R-500 I think, it is rated at 500 ma,  don't recall if good below 80m, check the ad!   The ART13 one is wound with coated nichrome wire! very good at suppressing parasitics. Think this national one is too, will show only an ohm or so.

Thanks! I'll check out the 53 handbook. Alan

I've had a 53 handbook since about 1953.  I never remember seeing that choke in the National catalog.  Most likely the choke is something made for a military xmtr.

The 1943 handbook shows the same National chokes as the 1953 handbook and doesn't include your choke.

Fred

Thanks Fred. I had checked out a number of the ARRL handbooks from 48-through the mid 50's and 60's. Looking at the National ads in the rear and did not see any reference either. Maybe I missed it. I think the reference to the ART-13 is probably the best link. Measurements on the choke imply it should be fine for a single 813.

A choke like that was used by Collins in the ART-13, 32V, and KW-1 transmitters. Maybe others. Even though they all look the same, the inductances vary.