[Boatanchors] SX-115 - the saga continues----

[Paul]

More on the SX-115 restoration:
   
  Now that I have all my new tubes installed I thought the last remaining steps would be to redo a complete alignment and then solve the low audio problem if it still existed.
   
  Not that simple.........
   
  Things were going great until I got to the 6.0mc to 6.5mc variable if alignment. I had problems here with my initial test alignment but hoped it was due to the very weak tubes in the chain. My hopes were dashed......
   
  Following the alignment procedure I adjusted T1 and T2 for peak with the sx-115 freq set at 3950kc and the sig gen at 6050kc. Peaking went fine. Then readjusted the sig gen for 6450kc and the sx-115 for 3550kc and tried to adjust the trimmer caps for C33A & B. Got a little peak on each, but sensitivty at the low end of the band was very poor and had very low audio. At the high end of the band, sensitivity (and audio output level) was fine. NOTE: The last few days when I had been reporting great results, it was all at the high end/phone portions of the band, hadn't tried the cw portion. Anyway, I continued to tweak around and found no way that I could get equal gain/sensitivity from the high end to the low end. 
   
  I have already checked the VFO linearity and output level (injection voltage), these values are all good.
   
  To make a long story a little shorter, I finally got to the point where I decided to remove the shield over C33A/B to see if the cap was possibly shorted, not expecting to find any problem. I mean, there should be nothing but a simple variable cap in there, what could go wrong? What I found is that the rotor plates for both the A and B sections had completely come off the rotor shaft and had jammed between the capacitor body and the shield, so there was no variable if action at all for the 6.0 to 6.5 if amp, the rotor shaft was turning but there were no plates attached. 
   
  I figure what is happening is that with no rotor plates, I have minimum capacity all the time, regardless of the main dial freq setting and ganged rotor shaft position. I figure minimum capacity of C33 in the variable if would equate to the if being set at the high end, or slightly above 6.5mc, all the time. So when I am aligning the if frequency at 3950kc, thinking that the variable if is at the low end of 6050kc, I'm really adjusting T1 and T2 at the 6500kc end of the if, not the 6050kc end, getting T1 and T2 well out of whack. Then when I shift the dial freq down to 3450kc, the variable if remains at 6500kc since there are no rotors to change the capacitance, so trying to peak using the C33A & B trimmers doesn't accomplish much. Without the variable if tracking correctly the gain just drops right off as the main dial frequency changes  down in frequency.
   
  Anybody have any thoughts or comments on my deductions?
   
  More important, does anyone have a spare C33A & B Tuning cap for the SX-115? There are no values listed in the manual, just the Hallicrafters part number 048-000506. 
   
  Next, figuring the cap may fall into the unobtanium catagory, anyone have any techniques for reattaching rotor plates to a rotor shaft with the expectation that they may remain attached?
   
  And finally, there are no instructions in the manual as to how to index the plates once I get a functioning cap to install. I did some measurements and find that while the main tuning capacitor will turn a full 180 degress (full maximum to full minimum capacity) from one end of the dial to the other, the gearing ratio leading to the variable if cap does NOT cause the rotor shaft to travel a full 180 degrees, it looks like the plates, when attached, will only turn roughly 150 degrees, so it does not go from full capacity to minimum capacity. So has anyone with SX-115 experience ever had the shield off cap 33A & B and have an idea if the cap is set at full capacity when the main tuning dial is fully to the end of travel, or is it somewhat less than full capacity?
   
  73, Paul W2EC