[HBR]160 M and WARC Coils

[amargosaent at iscweb.com]

This is a reminder to those presently investigating or contemplating
construction of new 1st oscillator coils to cover 160 meters and/or the
WARC bands.  I believe two different (and incompatible) 1st oscillator
circuits exist in the surviving population of Crosby HBR receivers.
That certainly was the case in  1969, and with receivers being sold and
re-sold, some without documentation or original builder's notes, it
would not be impossible to un-knowingly have the Hartley and not the
more common tickler coil design.

The tickler coil design is that shown in all of the QST schematics which
I hold.  The Hartley design was developed by Ted between 1965 and 1968
to improve the instability in his original tickler coil design.  He had
plans up through 1967 to publish final results in QST once he was
satisfied with ability of others to execute the design.  Long-term
health problems began creeping up on him in1968 (he was then 71 years of
age), and he was emotionally pretty-much burned out in supporting new
HBR construction by  others.  I do know he was approached in 1969 by
both ARRL and Bill Orr about publishing another QST article  (which
would have included the Hartley stuff), but I never saw it in print.

Despite the lack of publication, about a dozen of us (I was one) built
the Hartley version in 68/69, and Alex Stewart in 1970 convinced Ted to
provide construction data to another 25 builder/experimenter types,
which he did.  To my knowledge none of us had any difficulty executing
the Hartley design (Ted's biggest nightmare) and its superior
performance makes it almost certain that the 40 or so who did build it
passed the good word to others.  The conversion is easy and clean; Ted
was kind enough to wind my 80m Hartley coil himself, then observe me
wind the 40m  right in front of him - I made no mistakes, followed his
verbal alignment procedure, and both coils worked "straight out of the
box" (much to our mutual amazement and delight!).

There is no way now to know how many were built (I can personally
testify to 6) but it would not surprise me to find the number was upward
to 100.  Good possibility a few of those are still around eager to get
their own 160m and WARC coils.

Which oscillator do you have?  Easy enough to find out, especially if
you have working coils.

        The tickler coil design will have two separate windings, the
lower (and smaller) being the tickler while the upper tapped coil is the
oscillator grid tank.  All 5 coil form pins are used.

        The Hartley design will have no lower coil and a single coil
close or evenly space wound from coil form bottom to a tap point at
about the 1/3 turns point, those turns above the tap point transitioning
to a taper spaced winding. Only 3 of the coil form pins are used.

As a final check, look at the 1st oscillator wiring.  If it is a
Hartley, the main tuning capacitor will be connected between the coil
top and bottom, with coil bottom grounded.  The coil top will connect
through a 100 pfd cap and RF choke to pin 1 (grid) of the 6CB6A 1st osc
tube.  The coil tap point will connect directly to pin 2 (cathode) of
the same tube.

Feedback needed for oscillation in the Hartley occurs through the tap in
the single inductor.  As the tap is moved up (toward the grid) feedback
increases; as the tap is moved down (toward the cathode) the stability
improves.  Hitting the "right spot" for the tap is one of the challenges
when doing a Hartley oscillator design.

Ultimately, those with the better performing Hartley oscillator will
need a different 160/WARC coil than those with the tickler coil
oscillator.  Also note that the Hartley is not specific to any of the
Crosby HBR numbered designs; it can replace the existing tickler coil
oscillator in any receiver from the HBR 8 up through my HBR 20.  I would
recommend to present HBR  owners (those who are serious about using
their old relics on the air) a conversion to the Hartley design,
followed by custom temperature compensation.  Once accomplished, present
complaints about HBR instability will certainly diminish and in most
cases evaporate.  My worst-case performance (cold coil in cold receiver)
is thermal drift for 30 minutes after startup from power off, then
zero-beat for 6 hours; my best case (cold coil in hot receiver) is
thermal drift for 10 minutes and zero beat as before.  These figures
will not match 21st century solid-state digital designs, but it is about
as good as it got for any body's hot-cathode analog design of the
mid-20th century.

I plan to include the Hartley details, my own temperature compensation
procedure/results, and some un-published material and letters from Ted
in a sort of "builder's notebook" format.  Given other projects and
priorities, that document will probably not see light of day until
autumn 2007.  I need to finish the on-going overhaul of my HBR20 so I
can verify procedures and guidelines before seriously putting paper
together.

73 es Happy New Year de W6HHT/Jay