[Hallicrafters] RE: SX115 Mode switch problem on LSG

[Paul]

Hi Mike,
   
  Here's one I think I can help you with based on my current experience restoring/realigning my "new" SX-115.
   
  I'd bet that what has happened is your 955kc third conversion oscillator has quit functioning. This is probably due to either the 955kc crystal going bad (highly unlikely), the 3rd conv oscillator tube (V10, 12AT7) having the 955kc side of it's duo triode tube going bad (possible), or the 3rd conv oscillator coil being out of alignment (highly likely). This coil is T6 and located on the top of the 3rd conv oscillator assembly, next to the two oscillator crystals, 1055kc and 955kc. Fortunately the 955kc oscillator is adjusted from the top so you don't even need to turn the radio over, just pop open the top. While the specific alignment instructions are in section 5.4 of the manual, a quick check can be done as follows: All you need do is locate T6, turn the radio to the LSB position (AM or SSB/CW), and slowly rotate the top adjustment of T6 left or right a few turns until the radio starts functioning in the Lower switch position. This should only be a few turns hopefully.
   
  What is happening is that this coil sets the activity level of the crystal. If it is not set properly, the crystal stops oscillating. To set it, you find the point where the crystal is working, then as you rotate in one direction there will be a point where the crystal activity drops off almost immediately. Rotating In the other direction, the signal level won't cut out immediately, but it will gradually reduce in level. Don't set it too close to the sharp cutoff point, as if it is too close, then when you switch from Upper to Lower, you may find that the radio will respond (come back to life) sluggishly, or not even come back at all. Of course the best thing to do is an alignment of both the Upper and Lower 3rd conv oscillator, as the setting for the Lower side is dependent on proper setting of the Upper side initially. Just because Upper is working now, it doesn't mean it is at optimum.
   
  Hope this helps.........
   
  73, Paul W2EC