[Boatanchors] SX-71 Restoration

[L L bahr]

I worked on the Hallicrafters SX-71 project this afternoon and removed the front panel and restrung two of the four dial strings.  I restrung both Tuning Dial Strings and not the two Slide Rule Strings as these were in good shape. 
  
Here is what the instructions and storybooks don't tell you!: 
  
1.  The toggle switch nut remover to remove those fancy panel nuts holding the toggle switch in place worked like a dream.  This is the first time I used it.  You twist the handle to tighten a grip on the nut and then you just  turn the tool to remove the nut.  (No fuse no strain and you don't bugger up the fancy nut so it can be used again.)  
http://www.stewmac.com/Luthier_Tools/Tools_by_Job/Electronics_and_Pickups/Adjustable_Toggle_Switch_Wrench.html   I wish I had one of these a long time ago! 
  
2.  To get the radio prepared to restring dials you must first: 
  
A. Remove knobs (three different Alan and Bristol wrenches),  remove switch nuts, remove jack nut, remove panel screws.  Now pull off front panel. 
B. Remove top brace covering dial pulleys by removing 4 screws. 
C. Remove 4 lamp holders,  (Two have 2 screws and the other two have one screw each.) 
D. You need to remove the meter.  
     1.  Cut the two meter wires near the splice.  DO NOT LOOSEN THE TWO METER NUTS ON THE REAR OF THE METER TO REMOVE THE WIRES.  When you re-install the meter re-connect the splices and use new heat shrink tubing as Hallicrafters did when they first built the receiver.  (If you loosen the meter nuts where the wires attach, you will POSSIBLY DAMAGE THE METER.) 
      2.  You now need to remove three front screws to remove the meter.  WARNING!  The small screws each go through a small hollow bushing and the threads of the screws go into the rear panel.  You need to hold the bushings with a needle nose pliers so they don't go flying when you remove the screw.  After this is done, you can pull out the meter. 
E.  Now remove the screws holding the dial face panel.  At this point you can slide it left or right to remove it.  Be careful not to damage the side rule dial strings.  At this point you can now start the restring process.  As said earlier, there are 4 separate dial strings.  My two slide rule dial strings are OK and I didn't have to replace them  That is a BIG DEAL because you would have to re-string all 4 strings if the slide rule strings are bad.  That means removing the drive strings first as well as their drums before you could replace the slide dial strings.  Also, the slide rule strings hold the dial pointers on both the top and bottoms of the string.  Hallicrafters glued the pointers to the strings.  To replace these strings means careful removal of the pointers from the old strings.  In my case the dial strings were in good shape.  However the LEFT main drive string was broke and when I inspected the band spread drive string, it to was about to break so it needed restringing too! 
F.  You need 26 inches of dial cord for the two main capacitor drives and you need 66 inches for each of the two slide rule strings.  I used some dial string I had around here .028 inches in diameter.  (Can't remember where I got it.)  This is just slightly larger then what Hallicrafters used.  Follow the directions in the Hallicrafters manual for restringing the dials.  I did use some blue masking tape and I made sure I had tension on the dial cord spring.  It worked the very first time on the LEFT drive.  (I had set up the capacitor drum as in the Hallicrafters manual picture.  I DID NOT USE ANY VIOLIN ROSIN OR BEESWAX.  No problem, this was a piece of cake and there was no slipping of the dial string on the 1/4 inch shaft.  (I did lubricate all the pulley shafts so the pulleys could turn freely without binding.  I'll do the same on the capacitors but for now they turn freely without any lubrication.)  IF YOU CLOSELY READ THE INSTRUCTIONS, YOU ARE TOLD TO MAKE SURE YOU WIND 3 1/2 TURNS AROUND EACH 1/4 INCH SHAFT!  The pictures shows points 1,2, 3, etc but it does not show you how many times to go around the shaft.  They warn you if you do not do 3 1/2 turns, the dial could slip.  I think this process gets a lot of people in trouble as they just follow the pictures rather then making sure you wind 3 1/2 turns around the shaft.  Consequently they may only have 1 1/2 or 2 1/2 turns installed.  There then may not be enough friction to turn everything.  With the 3 1/2 turns I see no indication of any slippage. 
G.  Now the REST OF THE STORY!!!  I set the slide dial on the right hand dial to the LEFT just as in the picture in the manual.  BAD IDEA!!!  If you string it this way the dial won't move hardly at all.  You need to have the dial pointer on the right hand side of the receiver, that is, the band spread dial as a mirror image or in other words the dial needs to be on the right hand side of the scale in order to re-string this dial string correctly.  After realizing this and restringing it with the dial on the right hand side, it too worked flawlessly.   
H.  At this point the dials are all working just fine.  While the front panel is off I am going to blow out all the dust and clean all the metal.  You can also attempt to clean part of an exposed rotary switch at this point.  I think I am going to repaint the two RED dial pointers as they are almost a maroon color at this point.  It would be smart to install new #47 lamps at this point or long life equivalents.  I might experiment with LED replacements which are made in single as well as multi LED pin ball lamps.  However, they may be too bright or cause unwanted shadowing.  
I.  One last thing.  MAKE SURE YOU REPLACE THE 20 INCH LONG TOP PROTECTIVE SHIELD BEFORE TURNING THE RADIO UPSIDE DOWN WHEN PLACING IT IN A WORKER'S JIG.  If you don't have this shield in place all the weight of the receiver will be on the slide rule dial string pulleys.   
  
Before you replace the front panel by doing the reverse, make sure all four of the dial strings are in good shape.  Believe me, you don't want to be doing this again soon! 
  
I'm done for the day! 
  
Lee, w0vt