[Hallicrafters] SX-73 VS: SP-600-JX Comparision question

Thu Nov 4 08:26:27 EDT 2010

As a quick follow up:

The SX-73 audio certainly is more than sufficient for a 10-12" speaker in 
home use, that is how I use it and it is not objectionable. The output iron 
is much heftier than say a SX-71 and the bass response is good.

The ballast tube can be replaced by a 6V6 and not lose the regulation.

The AN/GRR-2 I worked on had potted transformers and MFP but I dont remember 
anything else different from a standard SX-28A.

Ive never seen a military SX-32, I have a plain vanilla model and 3 versions 
of the SX-28.

The SX-73 fits in a regular Hammond cabinet which helps it look better in 
its domestic location. The basement holds 2 racks of military and commercial 
receivers; no way I could bring that upstairs!

Carl
KM1H

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
Cc: <Hallicrafters at mailman.qth.net>
Sent: Thursday, November 04, 2010 5:12 AM
Subject: Re: [Hallicrafters] SX-73 VS: SP-600-JX Comparision question

>
> ----- Original Message ----- 
> From: "Greg Mijal" <bluebirdtele at embarqmail.com>
> To: "Carl" <km1h at jeremy.mv.com>; <anchor at ec.rr.com>;
> "Richard Knoppow" <1oldlens1 at ix.netcom.com>
> Cc: <Hallicrafters at mailman.qth.net>
> Sent: Wednesday, November 03, 2010 6:30 PM
> Subject: Re: [Hallicrafters] SX-73 VS: SP-600-JX Comparision
> question
>
>
>> Here's my two cents worth.
>> I've had two of the SX 73's (R 274 version)
>> It's more or less identical as a deluxe band cruiser.  The
>> biggest
>> difference in performance is the sheer sound volume of the
>> SX 73.  It uses
>> the big bulb version of the 6Y6 and has enough volume to
>> literally be heard
>> across the street. Sound quality is the same for
>> Hammarlund and Halli.  The
>> sx 73 also uses a ballast tube (R80) for filament
>> stabilization but will run
>> without it just fine on HF.  The SX 73 is also lower in
>> the overall parts
>> count.  One thing odd about the SX 73 is that if you use
>> it with a
>> transmitter.  The AVC takes a long time to recover and you
>> will miss the
>> other stations first three seconds or so of transmission.
>> Halli later added
>> a relay to over come that and mounted it to the back
>> frame.  The SX 73 meter
>> is also very scotch. SX 73 parts are very difficult to
>> come by these days.
>> 73's
>> Greg
>> WA7LYO
>> Kinston NC
>   Thanks to all who answered. I've been curious about this
> "other" version of the R-274. From just the schematics it
> appears to be a very well thought out receiver. It would be
> interesting to know the history of its production because it
> was obviously made to meet the military spec for the SP-600.
>    A couple of observations:
>    The SP-600 has no band spread. It has a logging dial
> which can be calibrated for any band of interest but the
> tuning rate is a bit high for normal ham use. The tuning
> mechanism is perfectly smooth and has no play or backlash so
> its possible to tune it accurately for SSB if you have a
> delicate touch. The SX-73 appears to have the same
> arrangement.
>     About 25,000 SP-600'ds of various versions were built.
> That is a hell of a lot of receivers. I think only the
> R-390A was built in greater quantity. That makes it
> relatively easy to find parts. I suspect that not many
> SX-73's were built.
>     From the paper information I would not be surprized if
> the SX-73 was not even _more_ stable than the SP-600 but you
> can't really tell from that.
>     Audio: In general the quality to be expected from
> single ended amplifiers, especially those employing pentodes
> or beam tetrodes, is not high. Most of them are very simple
> using an output transformer directly in the plate circuit.
> That means the transformer carries the plate current so will
> have poor low frequency response. Also, without feedback the
> distortion of such amplifiers is rather high. There are used
> in many receivers for reasons of economy but in the SP-600 I
> think there was a space and weight consideration. The
> previous Super-Pro receivers all had rather high quality
> push-pull amplifiers. They also had separate power supplies.
> The first announcement of the SP-600 indicated it had a
> push-pull audio amp but the illustration was art work and I
> wonder if even a mock-up or prototype was produced. I think
> there simply was not enough room on the chassis for both the
> power supply _and_ a push-pull amplifier. The SP-600
> chasssis is not a standard size, being deeper than usual to
> make room for everything on it.
>    If you take the audio off the diode load at the back and
> feed it to a high quality amplifier you will be amazed at
> the quality. Of course, most broadcast stations now are so
> highly processed that you will only hear the distortion they
> like to think makes them sound loud. On a good souce the
> SP-600, and probably the SX-73 will be quite high fidelity.
>     I think a lot of SP-600's are in poor condition, that
> is, they work, but not really up to capabilities. For
> instance, the frequency calibration is often off as is
> tracking because of the design of the tuning capacitor.
> There are eight stators each held in place by three clamp
> screws with fiber washers. I think these drift mechanically
> with age. The idea is that all of the stators must be
> exactly centered and exactly parallel to the rotor and the
> stators should also match at the top and bottom. I've seen
> at least one site recommending plate bending, DO NOT DO
> THIS, you will ruin the tuning cap.
>     The capacitor in the SX-73 appears to be of a different
> construction and may be immune from this problem.
>     A further note: While H built SX-28/A SX-32 for the
> military I don't think they were originaly intended for that
> purpose. Those built under contract probably used mil spec
> components in some places. I have a Navy version of the S-36
> and it definitely has changes from the civilian version so I
> would expect other originally civialian models to follow
> suit.
>     Perhaps some day I will come by an SX-73 (or even an
> SX-28). I will say that the SP-600 and SX-28 are among the
> sexiest looking receivers ever built.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
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