Aligning my Hallicrafters S-108 communications receiver

[Mike Stamper]

I finished repairing my S-108. It was the second IF transformer. I secured a good used replacement, repaired the burned-out resistors (from the high voltage short of the previous transformer), and once again my Hallicrafters worked.

I went through the alignment process per the instructions in the manual. Instead of listening for changes in volume, I hooked my scope to pin 5 of the 6H6 detector, and viewed the amplitude of the 455kc carrier wave. I peaked the IF transformers, and adjusted the RF on each band. I used a brand new frequency counter to calibrate the RF generator for each step.

Regarding the RF alignment, I have a question. I assumed that I should have adjusted the RF trimmers/coils so that that calibration of the bandwidth frequency corresponded to the frequency on my RF generator. For example, I would set the generator to 28mc, set the tuning control all the way to the right (out of the circuit), and adjust the bandsweep to 28 mc. I would then adjust the trimmer so that the carrier wave would appear at the 28mc mark. Once the oscillator frequency was set (and accurate), I would peak the waveform using the mixer and antenna trimmers. Did I get this right? This seemed to work; however, I wasn't sure.

Another question: I don't have a 20uh inductor required to make the recommended dummy antenna, so I simply attached the RF generator leads to the antenna terminals. When everything was done, I attached a long-wire antenna (and ground) and re-tweaked the antenna trim using actual station signals. Is the dummy antenna necessary?

Have I missed anything? The radio works pretty well, except on the AM broadcast band, which is a little weak but may lack an adequately long test antenna. Thanks to all for responding.

[Sandy G]

Sounds like you did everything "by the book"-I'd try a better antenna.

[Reece]

Many times just bringing the signal generator lead into the vicinity of the antenna terminal on the radio, without actually connecting it, will give enough signal. Usually the weaker the signal from the SG the better for radio alignment.

Reece

[Celt]

Interesting; my brother's S-108 had a bad IF can in it too. He never had any luck locating a replacement for it though.