On 02/13/2017 10:35 AM, Scott Stobbe wrote:
Hi Mike,
First of all, Wow what an interesting read, thanks for sharing
some of the history and your experiences with the 105. A second
thanks for uploading the manual, which I found to be a great
read, as with most old test & measurement product manuals, they
are far from just marketing fluff.
Bare with me, I'm not well versed in early radio history, but, I
also found it neat they choose to crystal calibrate on the 3rd
harmonic of the VFO to help prevent injection lock and for
increased sensitivity (but that may be true of all frequency
meters of the era, don't know).
Based on the manual, the thermometer is thermally mounted to
crystal holder, allowing one to temperature compensate the
crystal calibration point. I didn't see a mention as to what
crystal cut they used. I would guess it is one with a flat
tempCo with no turning points for the linear thermometer scale
to be used effectively.
Attached is a plot taken from the manual, the VFO stability
strip-chart
Hi Scott,
I don't know what crystal cut they used. It took me weeks of
searching just to find what you read. It would be interesting
to learn how Lampkin calibrated the Lampkin 105.
Line voltage is critical. I was breezing along with 18 Hertz on
160 meters, then the line voltage here moved around for the 80
and 40 meters tests. I heard the drift and knew that my
calibration chart was not very useful at that point.
I like the portion of the manual that tells about building a box
out of Celotex with a plastic front to avoid drafts. Celotex
was an insulated ceiling tile that used to contain asbestos. It
sure looked nice on the ceilings in our house.
We used to spray our rooms with DDT too. It explains a lot.
Did you see the photos that I uploaded to Mods.DK? I like that
variable capacitor used for calibration. Simple, but effective.
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