> Amen, Rich!
> It is obvious that 160 meters was an after-thought with the
> 77 series from Alpha. Also, the 77SX tank coil is the same
> as the 77DX. (2 tubes vs one)
>
> Another one for the list is the SB-1000 from Heath. A suitable
> mica replacement is available from Ameritron for the tank
> door knobs in this unit.
The doorknob capacitor in the Heath is within its current ratings,
assuming you know how to read manufacturers data. I suspect it might
be within the rating in the ETO also.
The problem is ceramic capacitors of large value have temperature
stability issues. The capacitors often don't even come close to
manufacturers ratings for temperature stability.
For many years, Ameritron used HEC doorknobs. They were stable and
very reliable. Yet in the same time period, ITT Jennings capacitors
of the same published ratings drifted so bad they were useless.
When HEC purchased ITT Jennings and combined the manufacturing, HEC
capacitors had the same problems ITT-Jennings had. The engineer at
HEC told me building ceramic doorknobs to some temperature stability
rating was nearly an exercise in witchcraft, and their capacitors
almost never were as good as the rating indicated.
It was the temperature stability issue that caused Ameritron to use
use chip capacitors, not component current rating. NP0 capacitors are
NOT available in ceramic doorknobs, and even the N3300's had an
actual stability in more in the range of N9000. Had HEC's temperature
stability not decreased significantly upon the purchase and
integration of ITT-Jennings devices into their line, they would still
be using doorknobs.
73, Tom W8JI
W8JI@contesting.com
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