Scott AW15 Broadcast Sensitivity

[Michael J Boessen]

Hi, All:

I've been working on problems with the oscillator on this thing for 3 weeks, the problem being, on the red and green bands the oscillator dies at the low end.  I finally gave up and am hoping Kent King can find a coil wheel and tuning cap that match from a set of the right age.

Meanwhile, I've been fooling with what seems to me to be pretty mediocre broadcast sensitivity.  I have 2 symptoms that might be relevant.

1:  My broadcast antenna trimmer won't peak.  With a fairly weak local station at 1400 it gets better as I turn the screw CCW until the trimmer won't open up any farther.  I'm  hooked to a 70 foot long wire for an antenna.

2:  If I open up the broadcast contacts on that little cam operated antenna switch with a station playing on the broadcast position, it makes almost no difference in sensitivity. 

I traced out the primary side from the antenna post thru the antenna switch to the top of the antenna coil primary.  The bottom of the primary goes to ground as it should and the primary reads 31 ohms, which seems like a lot, but it has a ton of windings, so that might be right.

Tracing out the secondary circuit, I walked back from the grid of the RF tube, back thru the switch labeled  "grounding ring" to the top of the BC ant coil secondary.  The bottom of that coil on the schematic (attached) goes to the junction of a cap and resistor.  On my set it was soldered to the mounting lug right next to that point (ground) instead of to the adjacent terminal on the coil, which is the aforementioned cap/resistor junction.  (see photo).  I thought: AHA!  so I moved the wire to the cap/resistor junction like it shows on the schematic.  Now my broadcast sensitivity is a bit worse, the trimmer doesn't tune at all, and I have a parasitic oscillation at the low end of the BC band.

That solder connection to the mounting post looked very much original.  So, either my schematic is wrong, or there was a change for later models.  Does anyone know if there was a change where they moved the lower side of that secondary to ground?

Having gone through all that, does anyone have any other suggestion as to why my broadcast sensitivity is so mediocre?  With that dedicated RF tube, I would expect this set to really kick butt, and it performs about like a 4 tube TRF on my antenna.

Best

Mike