For the past few weeks, I've been comparing receive structures between the
Drake 4 series and Collins 75S-3 series. I'm surprised by the
similarities - as well as the differences.
Some obvious differences:
- Mechanical IF filter versus crystal or LC filtering;
-160m coverage ability;
- Tunable BFO versus PBT;
- Q Mult in 75S-3.
Similarities:
- PTO VFO with 1 kHz dial markings;
- Preselector (similar octave structure?);
- Crystal 1st LO (unlike early JA receivers during the same time period);
- Audio power and AF driver stages similar to R-4B;
- Extensive use of RCA jacks, including RF IN;
Collins, like Drake, used PBT in the 1950s and I'm curious why it was
abandoned in the S line. Perhaps too complex to use among
commercial/military/amateur users? In essence, the least common operating
denominator wins?
Both series use the chassis for the filament return, although Collins used
four (!) heater lines in the 75S3. I found Collins' treatment of the
headphone jack quite interesting. They use a resistive divider network to
load the output line during periods of high Z loads. Seems wholly
unnecessary given that the 4-ohm transformer tap is routed through the H/P
jack's N/C contacts and the 500-ohm tap makes use of the divider in which
one resistor is bypassed during insertion of headphones.
My recollection of the S line tuning feel is sketchy but I recall a superbly
designed VFO tuning mechanism onto the PTO -- probably at least as
mechanically well designed as the those found in the Drake 4 series?
Perhaps the Collins S line has a slight edge with quality of construction
and components although I've not taken a look at whether the 75S-3 uses
ceramic switch wafers versus Phenolic -- and whether they used Teflon
harness wiring (where Drake fails). I have nearly no operating time with
an S line and I was considering a purchase. But based on what I'm seeing in
the schematics, I'm not impressed enough to unload my bank account for a S
line. This may seem like a "trolling" exercise to some, but I find the
comparison between the two products to be very interesting especially when
comparing cost and evolution of their product lines.
Thoughts on the matter very much appreciated.
Paul, W9AC
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