The Collins S-line is not exactly ham band only. If you have enough
crystals you can have any 200 kHz, I think, of Hf spectrum between 3.4
and 30 MHz except for 5 to 6.5 MHz.

Using a remote RF gen with programmed steps instead of the xtals is
possible with only minor modification, I think. But perhaps an internal
synth would be possible, and could be made quiet enough to not detract
from the superb performance, better than most synthesized icoms and so
forth.

I'm told that for specific 200 kHz swaths, a 75S or KWM is a much
better receiver than the 51S-1, which has a very promiscuous front end.


Any thoughts?

Bret, I can't fully agree with you on several points. The KWM and 75S
receivers are pretty good but so is the 51S1. The 75S-3B/C are arguable
better when tuned properly and in good electrical condition and in
consideration of the available filters. The problem with SWLing, so to
speak, is that although movable (read: re-tunable) throughout the HF
spectrum, both the KWM and the 75S receivers require an "internal"
retuning to maximize sensitivity when the excursion is made outside an
adjacent 200 kHz segment. You'll note in the manual a reference to a
"field alignment". This is required when shifting a noteworthy amount.
The KWM and 75S have limited re-tuning ability via the front panel
(preselector). The 51S1, on the other hand, has a fully tracked tuning
system throughout the HF spectrum. Price aside, and given a choice of
the two types of receivers, the 51S1 would wins hands down, in my mind,
as an SWL receiver. Frankly, though, I'd prefer and in fact use, among
others, R-390As or a Drake R4C (or "B") and an S&S DVFO-II. But, that's
why there are Fords, Chevys, and Toyotas.
de Jeep/K3HVG

Bret Ludwig wrote:
The Collins S-line is not exactly ham band only. If you have enough
crystals you can have any 200 kHz, I think, of Hf spectrum between 3.4
and 30 MHz except for 5 to 6.5 MHz.

Using a remote RF gen with programmed steps instead of the xtals is
possible with only minor modification, I think. But perhaps an internal
synth would be possible, and could be made quiet enough to not detract
from the superb performance, better than most synthesized icoms and so
forth.

I'm told that for specific 200 kHz swaths, a 75S or KWM is a much
better receiver than the 51S-1, which has a very promiscuous front end.


Any thoughts?

Bret Ludwig wrote:
snip
I'm told that for specific 200 kHz swaths, a 75S or KWM is a much
better receiver than the 51S-1, which has a very promiscuous front end.


Hi,

I have an S/Line, KWM-2 and a 51S-1. The 51S-1 front end is fine
if it sees 50 Ohms. It has a double-tuned front end which is quite
selective when used with a proper antenna.
If you must use a random wire antenna with a 51S-1,
even an untuned preamp such as an E.F. Johnson electronic TR switch
will help the front end perform as designed.

Below 2 MHz, the 51S-1 is insensitive, and was intended to be used
with an external antenna tuner/ source follower for 50 Ohm input
to the receiver.

My only gripe against my 51S-1 is that the S/meter zero
drifts quite a bit, and I don't look forward
to chasing down a possibly leaky coupling capacitor
in the IF circuit.

73,
Ed Knobloch

Hello Ed:

I had a similar problem and I kept looking in the wrong spot. I assumed it
was a leaky cap and replaced all the caps and tubes. Finally, out of
desperation, I convinced myself it had to be something else. About that
time I was reading about resistors. The carbon composition resistors are
often absorb moisture and change resistance when heated. Changing to a
newer more stable resistor solved the problem. I think there is a chance
you are affected with the same problem.

73, Colin K7FM

COLIN LAMB wrote:
Hello Ed:

I had a similar problem and I kept looking in the wrong spot. I assumed it
was a leaky cap and replaced all the caps and tubes. Finally, out of
desperation, I convinced myself it had to be something else. About that
time I was reading about resistors. The carbon composition resistors are
often absorb moisture and change resistance when heated. Changing to a
newer more stable resistor solved the problem. I think there is a chance
you are affected with the same problem.

73, Colin K7FM


Hi, Colin

Thanks very much for the hint.
Do you recall which resistor was at fault,
or did you change out several at one go?

73,
Ed
K4PF

K3HVG wrote:
Bret, I can't fully agree with you on several points. The KWM and 75S
receivers are pretty good but so is the 51S1. The 75S-3B/C are arguable
better when tuned properly and in good electrical condition and in
consideration of the available filters. The problem with SWLing, so to
speak, is that although movable (read: re-tunable) throughout the HF
spectrum, both the KWM and the 75S receivers require an "internal"
retuning to maximize sensitivity when the excursion is made outside an
adjacent 200 kHz segment. You'll note in the manual a reference to a
"field alignment". This is required when shifting a noteworthy amount.
The KWM and 75S have limited re-tuning ability via the front panel
(preselector). The 51S1, on the other hand, has a fully tracked tuning
system throughout the HF spectrum. Price aside, and given a choice of
the two types of receivers, the 51S1 would wins hands down, in my mind,
as an SWL receiver. Frankly, though, I'd prefer and in fact use, among
others, R-390As or a Drake R4C (or "B") and an S&S DVFO-II. But, that's
why there are Fords, Chevys, and Toyotas.



I'd read the 51S was pretty broad on the front end, so much so that
selectivity from signals at various points was pretty low. I have
never seen one,actually. I have seen LOTS of KWMs and 75S-3s.

What advantage do purpose built VFOs have over generators like the HP
8656B, which can be had cheap if you will accept the rear-connector
versions? (I don't know why you can't just drill a couple of holes in
the front panel and put BNCs on and make up a couple of new cables
internally, for the huge difference in price, either, but that's
another story.)

Purpose built VFO's, as you call them, generally allow for presetting an
offset or offsets such that a "dialed-in" frequency reads out directly
in the use frequency rather than the actual mixing or insertion
frequency. Additionally, as with S-Line equipment, etc. that use
band-dependent, multiple mixing formulas, multiple offsets may be set
into VFOs such as the S&S unit I mentioned. Cost wise, they probably
cost the same initially but I'd hate to have to pay to repair an HP. I
personally have not experienced the front-end problems as you describe,
but then I generally use my R-390A's. The 51S1AF/551G sort of sit on
the shelf, looking pretty. I did an article on general-coverage for the
Drake "C" line via a purpose-built VFO in an ER article last year. You
might, perhaps, be interested in having a look at it.
Regards Jeep/K3HVG

K3HVG wrote:
Purpose built VFO's, as you call them, generally allow for presetting an
offset or offsets such that a "dialed-in" frequency reads out directly
in the use frequency rather than the actual mixing or insertion
frequency. Additionally, as with S-Line equipment, etc. that use
band-dependent, multiple mixing formulas, multiple offsets may be set
into VFOs such as the S&S unit I mentioned. Cost wise, they probably
cost the same initially but I'd hate to have to pay to repair an HP. I
personally have not experienced the front-end problems as you describe,
but then I generally use my R-390A's. The 51S1AF/551G sort of sit on
the shelf, looking pretty. I did an article on general-coverage for the
Drake "C" line via a purpose-built VFO in an ER article last year. You
might, perhaps, be interested in having a look at it.
Regards Jeep/K3HVG

I think ER is a noble effort but it's a little expensive for someone
who is not actively hamming.

The S&S I'm not familiar with but I remember AOR made the dual section
vfo that replaced both the xtal section and the pto on S-Line. Looked
vaguely like a tiny S-Line. I guarantee it would be no cheaper to fix
than a synthesized HP if you were not too concerned with the precision
of the attenuator of the HP. In fact if you can get a 8656A that was
not field upgraded to the PIN diode attenuator, and the mech attenuator
went bad, (they do) I doubt it would bring more than a hundred bucks.
Use it straight through at +13 or +17 or get the little rotary stepped
job IFR uses in the 500/1200. I knew a guy who worked there who
summarily changed every one he worked on for over a year : he gave me
half a dozen and said they were all good under 400 MHz. IFR charged a
couple hundred apiece but they were like $60 from the source, maybe
Berkleley Varitronics.

IIRC the 8656/57 have 100 preset frequencies you can program in, so
you just use it channelized, since you only need to select for the
"band".

The limits on fixing 8640s is the presence of some HP custom IC's. I
have no idea if there are proprietary ICs in the 8656/57. In general
fixing HP equipment is easy. IFR is a mechanical nightmare but
electrically simple. Systron Donner-throw it off a cliff!

Someone suggested that the newer generation of arbs had the frequency
range and level to do the job and as well most are USB controllable. I
don't know if their spectral purity is good enough though.

The R-390 is the Marilyn Monroe of HF radios, though. Isn't it?

HiEd:

I recall I changed all of the resistors that were part of the bridge
circuit. I am not very good at keeping notes.

The new digital meters are nice to test components. Put a resistor across
the DMM and use a hair dryer. Works great when testing capacitors using a
capacitance meter.

73, Colin K7FM