Hartley Plate Choke

[Robert D. Keys/NA4G]

>
> I am in the process of building a VT-4-C (211) Hartley Oscillator
> transmitter for 80 meters (but want to have the ability to go to
> 160 meters) and have most of the components assembled, however, I
> would like to make the RF choke and want to make it out of small
> gauge magnet wire wound on a wood dowel.  Does anyone have any
> suggestions as to the size of wire, diameter of the choke (single
> layer wound) and the length (or turns)that would be suitable for
> 40, 80, and 160 meters?
>
> Your suggestions gratefully received.
>
> Rod, N5HV
> w5hvv at aeneas.net

Typically, in the old days at 200 meters and down, a coil form of anything
from 1 to 3 inches diameter was used, with a single layer solenoid or scramble
wound approach (most were single layer wound in the 20's but scramble wound
in the 30's and later on a bobbin like mom's wooden thread spool).  Use
wire sized to the requirement, and for a 50 watter that would be around
no. 26-30 or so wire, and use around 250-300 turns or thereabouts.
I usually reach for no. 26 or so, if I have it, or whatever rf chokes
the junque box will offer.  On a single bander Hartley puffer, it is
not particularly critical, and almost anything up to a mh or two will do
fine, and has always worked for me.  The minimum electrically needs to
be a 1/4 wave rf transformer at the design frequency.  Any coil with a
self-resonance of around 250 meters and more should probably work fine
on 80 meters, if the wire is sized to around 3 times the plate input
current requirements, in simple CW service.

Bob/NA4G

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