[EdHolland]

The patient survived the transplant, and is alive and well.

Before doing any desoldering, I tested the adjustment of the cores in the donor discriminator transformer. These freed up with only a modest twist of a plastic trimming tool - that was a good start. Then, on to desoldering and carefully untying the wiring to the transformer in the restoration. This was very time consuming, as I wanted to preserve component leads for an easier job with replacement. It seems I do need a better pair of needle nosed pliers for this sort of work. With that done, it was deja-vu all over again, as the donor part was removed from the junk chassis. It was cleaned up, and installed into the good chassis without too much trouble, save for re-twisting the component leads carefully.

Soldering complete, it was on to alignment. Again, I found adjusting the discriminator to be confusing. It calls for peaking up a dc measurement while adjusting the primary, and zeroing the dc offset while adjusting the secondary. Well, whatever I do, I can't get a sensible reading on the first measurement when using the recommended IF signal injection (8.3 MHz). Perhaps not enough injection signal, but the audio output certainly indicates that it is making it through. Following this method resulted in a pretty deaf radio with distorted audio. The discriminator was clearly well out of kilter.

So instead, I peaked up the IF stages, and adjusted the discriminator on to a station. A peak in volume followed primary coil adjustment, and clarity followed secondary adjustment. Result: nice clean tuning, stations across the dial, and clean audio

Next, I have to rig up something to tune up the Medium and Short Wave reception (standard 455 kHz IF procedures) but FM came first, as that is likely the primary demand from this radio.


Cheers,

Ed