[R-390] R-390A Cost Reduction and Improvements (was dead horse Hi)

[Jim Miller]

For what it's worth, the Collins Cost Reduction Project Document available
at http://www.r-390a.net/faq-refs.htm identifies the following apparent
"improvements" investigated for the R390A "A model" as compared to its
predecessor (R-390).  With these improvements, which model would you want?

** B+ filter improvement - Reduction of receiver temperature caused by
location of the type 6082 tubes, reducing the cost of the B+ filter.
** Added a VR tube to get the required stability from the VFO and crystal
oscillators.
** Mechanical filter designs incorporated for improved selectivity -
although phase nonlinearities did impact DF performance;
** Improvements in accessibility, reliability and performance;
** Savings resulting from elimination of the squelch facility and remote
control;
** Repackaged power line filter;
** Tuning control stops of improved design;
** Crystal oscillator redesign to reduce/consolidate crystals - A new
frequency scheme permitted a greatly simplified mechanical construction and
gearing,
** RF and variable IF coil redesign to improve tracking;
** Savings resulting from elimination of the 3500 cps low pass AF filter,
retaining the narrowband filter.
** Mainframe redesign for cost and weight reduction.
** Eliminated need for hum balance control;
** VFO end point adjustment was made more accessible. In the R-390A;
** Holes were provided in the gear plate so that this adjustment could be
made without removing the VFO or RF units.
** Simplified design and improved the performance of the gear train and slug
racks;
** Redesigned RF module to remove an RF amplifier stage (for cost savings),
put mixers on AGC control, use 6DC6 tube for RF amplifier, etc. - probably
the most controversial change, next to mechanical filters.
** Calibrator using a 200 kc crystal was built and tested. In comparison to
the former model using a 1 mc crystal, reliability was improved and harmonic
out-put increased.
** Where possible tubes were replaced by more rugged equivalents.
** Improved antenna relay provided to overcome poor attenuation in original;
** Changes in mechanical construction were also made, such as the closer
attention paid to electrolytic corrosion, the new means for chassis mtg. and
the radical power supply unit redesign.

Personally I'll take a 390A any day.


> Go to  http://www.r-390a.net/faq-refs.htm