Re: S-20R, S-40B, R-26/ARC-5
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Could not speak to who influenced the design of the Command receivers but a word of caution. If you have followed their history, be aware of the likely failure of those neat looking can bypass capacitors. My BC-453 began experiencing failure of those decades ago after 10 years of excellent service starting in the mid 60's.
Before applying a new power supply it might be wise to just go ahead and replace all of those with new ceramic bypasses. The oil filled cans deteriorate even when not in use and go dead short. I was able to see the burn paths clearly through the mica after failures.
Otherwise, enjoy the restoration. No reason it should not still be a good performer.
73 ... Ed, WA9GQK
On Friday, March 14, 2025 at 05:08:41 PM CDT, Maynard Wright via groups.io <m-wright@...> wrote:
I bought my first piece of radio equipment in 1957 at age 14, an
R-26/ARC-5 command set receiver. I still have it but haven't used it
for years.
I'm pondering working up a power supply for it to get it back on the
air, probably paired with my Multi-Elmac AF-67 transmitter, which is
usually paired with my S-40B.
In looking over the schematic of the R-26 and thinking about the recent
discussions of the circuitry of the S-20R and S-40B, I note a lot of
similarity between the command set receiver and the Hallicrafters. The
command set uses 12 volt tubes while the two Halli receivers use 6 volt
tubes, some of them equivalent except for the filament voltage.
The R-26 includes no band switching and covers 3-6 MHz which are the
main differences between it and the two Hallicrafters receivers. The IF
frequency in the R-26 is also much higher, at 1415 kHz, not a practical
frequency for the bandswitched Hallis with coverage down to the low end
of the BC band.
The most interesting (to me) similarity is the use of "gimmick"
capacitors in all three receivers to couple the BFO signal to the
transmission path:
S-20R C15 twisted leads to form small capacity
S-40B C38 2 mmf. "Gimmick" (in schematic)
twisted wire assembly (in parts list)
R-26 C33 <2 mmf. wiring capacitance
The S-20R also uses a "gimmick" to couple the high frequency oscillator
signal in the mixer stage (C38).
I haven't looked in detail at other makes of receivers from the '30 and
'40s, but I wonder whether the S-20R and the R-26 were just reflecting
similarities due to good engineering practice of that era, or did
someone from Hallicrafters influence the design?
73,
Maynard
W6PAP
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