SP-600-JX-14, #9396


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This is an SP-600-JX14, serial number 9396, Signal Corps R-274C/FRR, order no. 3376-Phila-52 (1952, that is).

I personally feel that the JX-14 is the best of the SP-600 series (this is a subject of debate, I know). It has a clean AGC system where they don't try to feed the AGC voltage to the second mixer, and the RF stage get the full attenuation of the AGC. I feel this AGC architecture helps keep the IM down in the two RF amplifiers.

I replaced all but a few of the tubes with NOS. I put a 6BZ6 in the 1st RF slot to increase the sensitivity. The tuning dials and the band selector readout were in good shape, so I didn't change them. The band select readout, however, was flaking off, so I did apply an overlay there. I had to replaced the AF potentiometer - the old one was scratchy. I also replaced one of the front panel switches

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I did wash and scrub the sheet metal with a scrubby sponge. No steel wool was used in the process. For the rust stains, I used a stainless-steel bristle brush about the size of a large toothbrush. I replaced the RF connectors for the IF output and antenna input with new silver-plated connectors.

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This is where I spent most of my time. The RF deck is the heart of the receiver. It has about 30 capacitors inside it. I replaced all of them, plus replaced the odd out-of-spec resistor and a few suspicious-looking wires. Although I don't try to include crystals with the receiver, I did test the FCU to make sure it works properly on all 6 slots. I replaced the RF connector with a new silver-plated one. I actually took this picture right after aligning the receiver, so the hole caps over the alignment access holes were not in place.

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All the bypass capacitors in the IF and AF sections were replaced with the SBE 716P "orange-drop" capacitors. High frequency sections got ceramic capacitors with 500V ratings. I routinely use 2% silver solder on all joints. I went through and reflowed many of the solder joints (but not all of them). I did test each and every resistor in the unit. A few of the mica capacitors were leaking, and were replaced.

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This is the rebuilt power section. I replaced the electrolytic with 47-uf, 450-V special high-ripple tolerant, long-life, electrolytics. You should be able to pass this one down to your grand-children.


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De-Oxit was applied to all the tube sockets. The chassis did not need any major work - it was relatively straight and square. It was apparent that this receiver had not been dropped or otherwise mishandled. There were no bent edges or crushed corners. I replaced the missing tube hold-down clip on V17.

All the miniature tubes have the IERC heat-sheding shields or their Cinch equivalents. These are the only tube shields known to actually increase tube life.