06-24-2019, 12:02 AM
Woo hoo! Success at last. Plate bending... lots of trial and error! What I found was that when I got the compensator caps tuned in for maximum sensitivity at the high end of the band, the sensitivity was quite low on the low end of the band. By tuning the compensator caps, I could greatly increase the sensitivity on the low end. In my case that meant decreasing the capacitance of the compensator caps on the RF and 1st IF compensators that are on the tuning capacitor. So, to bring that into line, I had to decrease the capacitance of the plates on the tuning capacitor. I tuned the compensators for 1.4 mhz. then tuned to mid band. Bending the slotted plate out reduces the capacitance. I checked to see if i was close by seeing if I could increase signal using the compensators. If I could, I increased the bend on the plates. I then retuned at 1.4 mhz and checked again. I repeated this procedure until I was reasonably close. Then I moved on to 600 khz with the compensators tuned for 1400 khz. In my case, I could again increase sensitivity by reducing the capacitance of the compensators. so, that meant bending the slotted plates out of the now almost fully "engaged" tuning capacitor. I would then repeat the process by re-tuning to 1400 Khz and then re-checking at 600. this is a back and forth process until there is reasonably good tracking on all 3 gangs of the tuning capacitor.
If the oscillator is not tracking, you can do the same thing by tuning at 1400 with the compensator (most of the tuning capacitor is not "engaged") and then checking at lower frequencies, noting whether you need more or less capacitance in the "engaged" portion of the tuning capacitor for the indicated frequency. I would say that if you want to improve tracking of the oscillator, do that before the RF and 1st IF tuning. I am known to confuse myself in the process so think it through to determine whether you need more or less capacitance. e.g. If a 1000 khz signal reads on the dial at 1100, there is too much capacitance when the dial is at 1000. So bending the "engaged' slotted tab out will reduce the capacitance. Remember, only the engaged portion of the capacitor is contributing capacitance. Like I said, it is easy to get confused in the process and bend the wrong way! Been there, done that! it's kind of satisfying to get it tuned in better than it probably was ever tuned by the people on the assembly line.
I rarely have seen the tuning plates bent on a "production" radio. But I have seen pics of the tuning capacitor of a McMurdo Silver and noticed obvious bending of the outside plate. Same with my Scott 16A. There was obvious tweaking to make it track.
Feel free to call me, Ron, if this doesn't make sense. You have my number!
If the oscillator is not tracking, you can do the same thing by tuning at 1400 with the compensator (most of the tuning capacitor is not "engaged") and then checking at lower frequencies, noting whether you need more or less capacitance in the "engaged" portion of the tuning capacitor for the indicated frequency. I would say that if you want to improve tracking of the oscillator, do that before the RF and 1st IF tuning. I am known to confuse myself in the process so think it through to determine whether you need more or less capacitance. e.g. If a 1000 khz signal reads on the dial at 1100, there is too much capacitance when the dial is at 1000. So bending the "engaged' slotted tab out will reduce the capacitance. Remember, only the engaged portion of the capacitor is contributing capacitance. Like I said, it is easy to get confused in the process and bend the wrong way! Been there, done that! it's kind of satisfying to get it tuned in better than it probably was ever tuned by the people on the assembly line.
I rarely have seen the tuning plates bent on a "production" radio. But I have seen pics of the tuning capacitor of a McMurdo Silver and noticed obvious bending of the outside plate. Same with my Scott 16A. There was obvious tweaking to make it track.
Feel free to call me, Ron, if this doesn't make sense. You have my number!