[HBR] HBR -- Part 7

[Walt Hutchens]

Here are the pictures with the oscillator coil and wiring. They're
more interesting if you click the 'magnify' button at the upper right:

http://picasaweb.google.com/timbreblue/Walt#5261666031775899570

You can see the raised mounting of the oscillator tube. It's the one
to the right of the shield, next to the empty IF transformer hole.

http://picasaweb.google.com/timbreblue/Walt#5261666323291227186

The allen wrench in the Fahnstock clip is for the shaft couplings and
knobs.  The tuning cap shaft extension is a rusty piece of scrap I had
on hand; I'll find something better, eventually.

http://picasaweb.google.com/timbreblue/Walt#5261666451689928738

The oscillator socket is the ceramic 9 pin miniature toward the lower
left.  The dabs of masking tape all over the place hold the wiring
in place as I go along; when finished I'll lace it.

The 1st IF and S-meter circuits are wired. It picks up the signal from
my GDO and the S-meter deflects, so all that is working.  There's a
trace of hum (at full volume) on the (pure) signal from the GDO so
that will have to be looked into.  Most likely, heater-cathode
leakage, probably in the plate detector stage.  Second choice,
inadequate filtering of some high voltage.

One definite problem is that there's an offset of about -0.7V on the
AGC line, evidently coming from the vacuum diode I used in this
circuit. "Shucks, I should have thought of that." There are some
options for dealing with this; I don't know which I'll try first.

The next construction step will be the crystal filter, 1st IFT, and
mixer circuit.

And a question: Does anyone have recommendations for securing of turns
on the coils?  Particularly on PVC-pipe coils?  I know that one should
do the bare minimum, because when I've coated the whole coil in the
past I got a lot more distributed capacitance and it was DRIFTY.
First, of all, it drifted steadily for a few weeks while the coating
dried, then it drifted excessively with each heating/cooling cycle, 
compared to a bare coil.

Since I'm using fairly heavy wire -- #22, roughly -- I am able to wind
these coils very tightly and that does help, but maybe a few dabs of
PVC pipe cement on each end? Plus where the gap is, near the tap? Maybe 
thin the usual cement a bit and just use dabs?  Or ????

Walt
KJ4KV