The AM Forum

   In preparing to align my SX-62 I find I have no bfo signal. I've measured the voltages at V10, 6J5 beat oscillator. I measure +150 at the plate, +51 at the grid and +46 at the cathode. Manual specs are +145, +17 and +28. I've measured the associated resistors and find that they are all high by 10-20% but nothing way out of site.

   Any suggestions will be appreciated.

Ed

It very well may be oscillating, but not within the passband of the IF.  Take a look at the plate of the tube with a scope and see.

Looks like, though, the tube's not drawing much current so it may very well not be oscillating.  If not, try another tube, then suspect the silver mica capacitors.

Thanks Johnny,
   I looked at the plate with a scope and saw nothing. Then checked the micas and they check good on my digital cap meter within 5%. The two inductors show continuity and measure about 4uH and 600uH. Tried another 6J5 with same results.
   I'm stumped.

Ed

Ed,

It is very possible that your scope probe is loading down the BFO enough to kill the oscillation.  You should be using a 10X probe with fairly low capacity and I would "probe" on the detector side (after the BFO coupling capacitor) to further reduce oscillator loading. Another trick is to couple the probe through a low value capacitor to reduce circuit loading as long as your scope has sufficient sensitivity to work with this setup.

It is likely that the BFO is oscillating too far off frequency as JN noted.

Also, is the BFO working OK on 10.7 Mhz (bands 5 and 6)?

Hi Rodger,
   I'm using a Tek 475A with a Tek x10 probe. I checked at the tube socket. I'll try your suggestions later this evening and see what I find.

Thanks,
Ed

Hi Ed,

For the first week of my 12 weeks as a novice an SX-62A was my station receiver.  Speaking from experience, after you get the BFO working you probably won't use it much.  Between the fairly fast tuning ratio and a bit of backlash from the "string" drive tuning CW signals (much less SSB) is a bit of a chore.  I used the BFO slug as a fine tuning control as a novice.  Fortunately a local ham loaned me a SX-101 and then I was really in business.

But the SX-62 is a great band cruiser with wonderful audio.  It continued to do duty pulling in AM broadcast (which sounded a lot different in the early 70's) and WLS out of Chicago would come booming into the MS gulf coast by late afternoon during the winter.  It is a great sounding and looking receiver.  If I ever get a ratty looking one I am going to mount a tuning eye tube in place of the h on the front escutcheon which I think will give it a nice look.

There is no BFO option on those bands, it runs at 455 kc.

A LCR meter can read those micas just fine and they can still have lots of leakage.  If you have a rice box xcvr with general coverage you should be able to hear it if its oscillating with a wire close to the circuit.

Carl

Carl,

It may not be very useful but it has the capability to receive CW via BFO injection on the high bands also with a 10.7 Mhz. BFO.   Check your alignment instructions for the 10.7 IF and you will find a step for setting the BFO on frequency.

Rodger,
    I checked the bfo on bands 5 and 6 after the coupling cap as you suggested and I got a healthy signal on my scope. I was able to measure it with my freq. counter at 10.8 MHz.
   On all other bands there is still nothing at 455 kHz.

Ed

I stand corrected, its something Ive never checked until today :-[ 

If it doesnt work on the lower bands Id start with tracing out that switching matrix and wiring.

Carl

Carl,

You spent too much time in practical engineering and logically assumed there was no reason to provide it on the highest bands :)  The BFO is of little practical use anywhere on the SX-62 given the dial backlash and lack of band spread and is especially useless on the two highest bands.  It did allow the marketing department to claim that it could receive CW on all frequencies and brag about the lower image rejection receiving 10 meters on band 5.

Ed,  did you check the BFO coil continuity to ground in the lower positions so that the short between the small and large windings is removed?  It should show measurably more resistance to ground (measure at the C101/102 junction to ground) on the lower 4 bands when the intermediate short is removed by the band switch.

Rodger,
   Just checked. I measure 10 ohms on lower 4 bands and 0 on upper 2.

   In looking over my schematic I see a brown wire that comes off the first coil but my schematic doesn't indicate where it is supposed to go. Do you have that info?

Thanks,
Ed

I should have mentioned that I measured resistance at the yellow wire between the two coils.

Ed,

Based upon your yellow wire measurement point the lower coil has continuity so it is likely to be OK. 

The SX-42 is a VERY close relative of the SX-62 (most of the circuitry is identical) so grab the SX-42 manual from either Bama or Nostalgia Air because it shows the full schematic with the complete brown wire circuit instead of the "hanging chad". 

Hallicrafters made all sorts of production changes during this time period and did a very poor job with schematics/documentation so do not be at all surprised if you find differences between how your receiver is wired and the schematic.  It is worthwhile to download all of the schematics from Bama for reference.  There is also no guarantee that mistakes were not made in the original build. My top-of-the-line SX-88 has little dots of red inspection paint on all of the connections but one of the connections had paint but no solder!  That says a little bit about the build quality and subsequent inspection.

   I looked at the schematics for the SX-62A and SX-62B and find there is no brown wire off the top of the first coil in the bfo can. I looked at the schematic for the SX-42 and found that the brown wire goes to ground thru a trimmer cap. There is no such cap in my SX-62 or in the schematic and I find no mention of it in the alignment procedure.
   In my rx the brown wire was connected to an unused pin of the bfo oscillator tube socket. Also connected to this pin was C99, a 0.05 uF tubular. The other end of this cap went to the plate circuit of the oscillator tube. According to the schematic this cap is supposed to go from the plate circuit to ground.
   Following the A model schematic, I removed C99 from the socket pin and soldered to ground. I left the brown wire connected to the unused pin (i.e. no connection).
   I now have a bfo. Tuning in slopbucket is tricky with the fast tuning rate but by no means impossible. Was able to tune sb on 75 meters without too much trouble.

   Thanks again to all who took the time to make suggestions.

Ed