Many thanks to SWLing Post contributor, Daniel Hawkins, who leaves the following comment in reply to our previous post about the Northern Radio SP-600 and discussion about diversity operation. Dan writes:
Diversity operation: two or more receivers and antennas used to copy CW or RTTY from one or more transmitters.
Most of the Hammarlund SP-600s were models built for diversity use including the well-known JX-17, the most common SP-600. Diversity models can be used as single receivers. In this eBay example Northern Radio has modified a SP-600 J-11 for diversity use.
SP-600 nomenclature: J means joint army/navy (JAN) mil-spec components. L means low frequency. X means crystal frequency control in addition to VFO. My SP-600 is a JX-21, which is not a diversity model. Higher model numbers do not necessarily mean later production dates. All SP-600s use the same serial number sequence regardless of model. Somewhere between serial numbers 15,000 and 17,000 (mid 1950’s) Hammarlund stopped using molded black beauty capacitors and switched to installing ceramic capacitors.
The two-digit model numbers indicate model types. JX-1, 7, 10 and 21 were similar non-diversity receivers. SP-600s built for military contracts will have an additional tag showing the military model number(s).
Here is a great page showing Northern Radio modified SP-600s in action with accompanying Northern Radio RTTY gear.
Many thanks to SWLing Post contributor, Dan Robinson, who writes:
Those of us who still use SP-600s, and those of us who once did but can’t deal with them in retirement, lust after some of the rarer versions of the radio. This is one of them, the Northern Radio modified SP-600.
I must say that when Dan finds these rare treasures on eBay, they usually carry a very hefty price. In my opinion, this is a good deal for a rare SP-600. Best of all, it has a BuyItNow price, so first-come, first serve and no bidding up the amount. The shipping price is a bargain considering this radio probably weights upwards of 80 lbs.
This SP-600 may need some electrical restoration and possible re-capping. It’s listed as: “For parts or not working.” If you’ve been looking for an SP-600 to restore, this might be worth consideration. Thanks again, Dan.
Many thanks to SWLing Post contributor, Daniel Hawkins, who writes:
One of my favorite Radio New Zealand International programs is Sunday Night with Grant Walker. This program is heard on RNZ in New Zealand from 8:06-10:00 p.m. and is run at the same time on RNZI. Sunday Night features hit oldies and one interview. Each program highlights oldies from one year. Last Sunday was 1977 and the week before was 1955. My video from last Sunday includes a favorite that I haven’t heard for many years.
The RNZI broadcast of Sunday Night is 0806-1000 UTC Sunday on 9700 kHz. That’s 1:06-3:00 a.m. Sunday, PDT. Definitely a show for night owls. West Coast reception is nearly spectacular for the distance: 6,600 miles from my location in Davis, CA, USA. The radio used for the video is a Hammarlund SP-600 JX-21, built in 1956 or 1957. Yes, the tuning dial is a little off on this band. I’m using the 8 kHz selectivity setting with fully advanced AVC. The antenna is a 106’ outdoor random wire. The speaker is antique as well: a 10” Jensen PM-10C with matching transformer connected to the 600 ohm audio output on the SP-600.
Wow! Thank you for the program recommendation, Dan! I, too, have an SP-600–there are few valve receivers that can rival it for both audio fidelity and sensitivity. What a beauty of a rig you have there!
Many thanks to SWLing Post contributor, DanH, who writes:
I have been working on my Hammarlund SP600-JX-21 for the last two weeks. Results of the filter cap replacement were encouraging. I’m going after an AVC issue that is probably capacitor-related as well before doing a re-alignment with the signal generator.
All of this activity has turned my attention toward vacuum tubes. I found three vintage industrial films online that caught my interest…
The Mullard Radio Valve Company produced The Blackburn Story in 1962. The film was shot at what must have been close the peak of vacuum tube mass production. This presentation is unique in its finely detailed documentation of miniature tube construction. The hand labor required to build some of these tubes is incredible, considering it is a mass production operation. A surprising degree of automation is present for manufacture of some of the more popular tube types. The video resolution is not the best but I found myself ignoring this limitation after the film got underway. I have a few Mullard tubes in my tube boxes.
Western Electric presents A Modern Aladdin’s Lamp (1940). This look at the electron tube is hosted by none other than Lowell Thomas. From the age of four pin and octal base tubes animation shows how tubes work.
Electronics at Work (1943) is a WWII offering by Westinghouse. The description of vacuum tube technology is a little more detailed and again animation is employed for visual impact. A variety of vacuum tube applications in industry and the military are shown from curing plywood to producing X-rays. The excellent animation was contributed by Famous Studios (when they weren’t doing the wartime Popeye cartoons).
LOCAL PICK UP ONLY Paso Robles Ca. 93446. Good condition, rack of Communications and Amateur Radio receivers. Includes Hallicrafters R-46B loudspeaker, two each Hammarlund SP-600 JX-26 receivers with one frequency readout as shown above the top receiver, a National NC-300 receiver with calibrator accessory, and a Hallcrafters SX-101A receiver with calibrator accessory. The rack cabinet is included. All have normal wear for vintage electronics, worn with faded, chipped and rust spots. The SP-600 receivers (both) dial slips and may need repair. All units may need further repair, alignment, or refurbishing. Local pick up only, I can help loading into your vehicle. 70hi 22wide 20deep weights about 600 pounds
I think this would be a great deal if all of the equipment was in working order. I suspect this seller hasn’t tested anything and is, most likely, not a radio enthusiast. I bet the reason the SP-600 dials are spinning freely is because the tuning lock is engaged on each unit–possibly a good sign that the previous owner took care of the equipment. All of it looks good (cosmetically) for its age.
If I were interested, I’d go by and check this out in person prior to bidding.
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