SP-600

(Click for full-size picture)	This is an SP-600-JX1, serial number 4579. It has the standard frequency range of 54O khz-54mhz. It is Signal Corps. R274A/FRR, Signal Corps order no. 1689-Phila- 51-01. It was made in 1951. I did refinish the front panel. I used a darker grey so the engraving and the dials stand out better. I did repaint the knobs on this one. They were quite dull. I did not try to repaint the meter. I was worried that some paint would get into the mechanism. I did put dial overlays on the frequency read-out, the vernier, and the band-change indicator (the originals are still there - I just turned them over and put the dial overlay on the "back" side). I made my own dial overlays from a more recent receiver. This receiver is unusual in that it has a steel front panel, rather than the standard aluminum. This adds maybe 10 pounds to the overall weight, but you don't have to worry about weapons discharge in your shack blowing a hole in this panel(!).
(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. In general, the MFP (Military Fungus Protection) has preserved the receiver in superb shape. There was no oxidation I could find except for the odd screw head that either missed the coating or was replaced later. The MFP is what gives the receiver its handsome chartreuse tint. De-Oxit was applied to all the tube sockets. The chassis did not need any work - it was clean 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 clips on V3, and V17.
(Click for full-size picture)	This is where I spent most of my time: the RF deck. All the caps were replaced with 600V ceramic. A number of resistors were replaced as well. I used a lot of shrink-tubing on the leads to prevent shorts but still allow you to get a tool in to align it. A number of wires were replaced. Several out-of-spec resistors were replaces. The caps were dressed to hug the ground plane wherever possible. I replaced the first RF tube with a 6JH6 for added sensitivity. Note the text above the serial number plate. This reiterates the procedure (noted above in discussing E13, behind the power supply) for converting for DF (Direction Finder) use. You move one wire from one screw terminal on E13 to the next.
(Click for full-size picture)	This shows the recapping job on the IF and AF sections. All the orange items are 600V SBE (née Sprague) "Orange-Drop" 716P capacitors. A number of resistors had to be replaced in this area as well. Several capacitors (C150, C164) were bad and were replaced. Most of the high-resistance (500K and greater) resistors were wildly out-of-spec and were replaced.
(Click for full-size picture)	Close-up of the IF and AF sections. Some amount of hardware was replaced by stainless in this area.
(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. This also shows the rectangular E13 terminal block (behind the power assembly). The two brass screws on the top are so that you can change the gain of the first two TRF stages from "Normal" to "DF" ("Direction Finding"). Doing that effectively disables the AVC on the TRF stages, running them at maximum gain all the time. In our modern world with 50KW broadcast transmitters on every hilltop, I would advise you to leave it on "normal." Note that this receiver has a different AVC structure from most others - the AVC voltage is supplied to V6 (6BE6 second mixer) and V7 (6BA6 gate) as well as the TRF and the IF stages.
(Click for full-size picture)	All the miniature tubes have the IERC heat-sheding shields. These are the only tube shields known to actually increase tube life. This gives you a good view of the pretty green hue the MFP provides.