IF not entirely successful…

After half a century one would expect the IF transformers to need a realignment. The method is simple.

  • Disable the local oscillator by simply grounding the grid.
  • Tune to the lowest frequency, i.e. approx. 3.5 MHz.
  • Alternately peak each core of each of the three transformers.

To do the peaking, a signal in the IF passband is required. The IF is about 1682 kHz. With the receiver tuned to 3.5 MHz enough signal leaks through to do the peaking. In the old days I used the local oscillator of another receiver as my signal source when I needed one. The best cost saving is no cost at all.

Some time ago I got an old Trio SG-402 signal generator. Luxury. The analog IM-5284 was connected to the speaker output so I could easily watch signal strength as I tweaked each transformer core. This was kind of a historic moment as this was the first time this millennium that the IM-5284 wss powered from batteries. I’ve mostly been using it for current measurements as I have several digital multimeters that works at least as well for all other measurements.

Signal generator on top of speaker. Meterman 37R in front used for frequency measurement. IM-5248 in background for signal strength measurement.

Alignment should be easy. It wasn’t. Some problems:

  • The signal generator was hard to turn precisely and didn’t stick well to frequency.
  • My body movements around the receiver influenced the measurements appreciably. I need to find a less care free way to introduce the signal into the receiver. See thin orange wire in photo! Some proper cables may be needed.
  • The large analog meter on the IM-5284 is wonderful but a little slow. Patience is required.
  • Minute adjustments of iron cores is difficult and more so when they are old. They tend to stick while you gradually increase torque, until they suddenly loosen and travel too far. Patience, patience, patience.

What I think I learned is that the adjustments needed were very small. With the inaccuracies in frequency etc. I am not even sure I improved anything.

I will try again, but I have to work on the first problem with the signal generator. I will try to devise a larger tuning wheel. For my Satellit 2000 I made an adapter to put on the tuning wheel when very fine adjustments are needed. I think I will try the same. Also, I consider opening the unit because the tuning did not feel smooth. I kind of expect to find a capacitor that hasn’t aged well. Familiar story?

If not entirely successful, try again! 🙂

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