Hi,

I bought a used 51S-1 about 15 years ago,
and it arrived with a burned-out antenna coil
for the 7 mc band (strange that the seller didn't notice that...)

All of the band change components are mounted on fiberglass
sections of a ten-section turret switch. To get at the parts
for repair, one must first remove the shaft of the switch,
and then the individual switch sections can be removed.
I'm mechanically somewhat ham-handed, but I managed it OK.

The 51S-1 seems a bit more stable than the 75S-3C,
I think because the PTO is not switched
to maintain dial calibration for USB/LSB operation.
Instead, there are two separate mechanical filters for USB
and LSB, and the BFO itself stays crystal controlled right at 500 kc.
The sideband mechanical filters are broad, about 2.8 kc,
and the c.w. crystal filter is 800 cycles bandwidth
(no variable BFO is included).
A.M. reception is via standard IF transformers,
with only about 5 kc bandwidth.
Collins offered an optional 6 kc mechanical filter for A.M.
They also offered optional 2.4 kc SSB mechanical filters,
and a 300 cycle c.w. filter.

The agc action is not that great, and the S/meter drifts a lot
in my unit - one of these days I'll get annoyed enough to track
down the source of the S/Meter drift. (+not+ caused by gassy
if/rf amplifier tubes).

Below 2 mc, the receiver is deaf without the (very scarce) 55G-1
low frequecy preselector.
Audio quality is pretty decent, and SSB is very
pleasant listening, if QRM is not a problem due to the bandwidth.

Selectivity before the first mixer is outstanding, based on the use
of double-tuned LC circuits before the rf amplifier.
If you connect the receiver to a random wire antenna,
you may be disappointed, because the receiver
really needs a 50 Ohm antenna system due to its front end filtering.
On occasion, I've used an E.F. Johnson TR switch between a random piece
of wire and the receiver input (it acts as a cathode follower
with 50 Ohm output), and the set-up worked very well.

The main tuning knob turns freely, so it is a good band cruiser.
There is a bit of clackity-clack audio noise while you tune away,
due to the turns counter which keeps track of which part
of the 1 mc band you are tuned to.
The PTO dial is marked in 1 kc increments from 0 to 100 kc,
and the counter display may be read 07.2 mc.
The tuning rate is about 30 kc per revolution.

In summary, the 51S-1 is a more than competant receiver,
with no really flashy features.
It doesn't give the operator much flexibility -
no variable BFO, no choice of SSB bandwtdths, AGC fast/slow, etc.,
so a knob-twister like me has nothing to do but listen
to the other ham (a daunting prospect!).

73,
Ed Knobloch

Phil Nelson wrote:
Someone is offering to sell me a Collins 51S-1 general coverage receiver, a
"winged emblem" model.

I'd be interested to hear how people would compare it to similar-quality
receivers. I can read the specs in the Osterman book, but what is it really
like to use, and how does it stack up against others? Any quirks, PITA
characteristics, standout features, etc.?