SP-600 JX 17 - RT's Radio Home Page
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SP-600 JX 17
Amateur Radio > Vintage Receivers
The Hammarlund SP-600 JX-17 is known as a "diversity" receiver. This one is dated February, 1954. It had been sitting in storage for a very long time. The main power supply filters and a few cracked "Black Beauty" capacitors were replaced before testing. I pulled the 5R4 rectifier and brought the tube filaments slowly to full voltage and let them burn for an hour or so. Reinstalling the rectifier tube and slowly bringing it up again brought floor noise from the speaker--it works! After cleaning the switches and aligning the high and low I.F. strings, it works fairly well but is a little weak on the upper (dual conversion) bands. The BFO injection is lower than it should be, but it receives SSB signals in "manual" mode with careful adjustment of the RF Gain, Audio and BFO controls. Overall, it is a promising receiver.
It was loaded with molded "black beauty" capacitors that must be replaced; some of these were in very inaccessible locations requiring significant deconstruction to access. Rather than replacing all of them at once, they were replaced a few at a time and testing. After replacing all of the molded and electrolytic capacitors as well as out-of-tolerance resistors, it is a stronger performer.
A close up view of the receiver as found. An IF Gain control has been added where the Tuning Lock was located; it is a 5K potentiometer between the cathode of V9 and chassis ground. It is a somewhat similar circuit to that is used in the R-320A version. The leads soldered to the original potentiometer were treated with the yellow tropical protective coating, so it appears to have been a military modification.
Here is the SP-600 listening on 40 meters with a better front panel installed.
This is the RF deck. Removing this unit is deep surgery. Removal was necessary to remove/replace the molded "black beauty" capacitors.