[Hallicrafters] S20R BFO dead

[SX-25]

Steve,

     I have never worked on an S-20R but I have worked on a lot of SX-25s which were descendants from the S-20R.
There are two areas I have found to be problematic in the BFO circuitry of the SX-25 (and I would presume similarly your S-20R). Obviously do the housekeeping first: 6J5 good, switch SW-3 good, IF/RF alignment good (or at least fair).

     Start with your connection from the BFO coil going to the 6SQ7 second detector. Hallicrafters used  an arrangement of two wires twisted together to induce the beat oscillation into the second detector. I typically can go from a strong beat note to none at all by moving this twisted pair arrangement around. So I get rid of it in my SX-25s. If you measure the capacitance of that twisted pair of wires it runs around 2 to 5 pf. So I eliminate it and insert a capacitor of between 2 and 5 pf in its place.

     Next, go over the oscillator with a fine-tooth comb. You will often find the terminals wiggly and wobbly and making dubious contact with the wire in the coil. Remove the oscillator coil from its can and give it a good once over. Draw diagrams as you do this and it will be easier when it's time to put it back together; but it looks more complicated than it really is. Once you have the BFO coil re-assembled and all connections intact, solder the coil's shroud can to the mounting bracket. This too has a stabilizing effect on lessens the BFO's variance-caused frequency wobble.

     Hope this helps. If I am speaking out of turn here because I have no S-20R experience and if I am leading you astray, I apologize. However this has been my experience with SX-25s.

     Rotsa ruck!

     WA9VLK