SP-600-JX-6, #15217

(Click for full-size picture)	This is an SP-600-JX6, serial number 15217, U.S. Navy model R-274B/FRR, order no. Nobsr-52039 19 October, 1954. This was a most remarkable unit. It looked to me like it had never been used. The tubes looked and tested new. All the wiring inside was brightly colored (it is generally so discolored that you can't tell one color from the other - they are all brown). The white wires were really, really white. All the insulation was in perfect shape - not flaking off or brittle. The problem was that the unit looked like it had been left out in the rain. ALL the hardware was rusted. This was the only unit where I felt compelled to replace ALL the hardware with stainless. Yes, every screw and every nut was replaced. The only exception was one screw that I couldn't reach. I took the entire RF unit apart to get in and replace the hardware. I replaced all the screws in all the sockets, and the screws that held the terminal strips on. There was quite a bit of corrosion stain on the chassis. I got as much off as I dared, but there is still some left. It is generally right around the tube sockets. On the other hand, this one had noticeably fewer out-of-spec resistors than I am used to. Generally all the high-value resistors are way out. Most of the resistors in this unit were just fine. This is the only receiver where I left most of the original tubes in place. They did not appear to have any wear at all, and tested strong. I replaced a couple with NOS, but that's all.
(Click for full-size picture)	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 connector for the IF output with a new silver-plated connector.
(Click for full-size picture)	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.
(Click for full-size picture)	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 one of the bathtub capacitors as well.
(Click for full-size picture)	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.
(Click for full-size picture)	I had to include this picture of the contacts on the turret blocks. Generally, these are stained dark or even black. You can't sand them, since they are plated with a very thin layer of silver. Sometimes you can use silver polish to brighten them up. This unit had absolutely the cleanest contacts I have ever seen. All they needed was soap and water. No fancy chemicals.
(Click for full-size picture)	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.