If no other fix comes along ,do this ;connect a series resonant circuit
to ground in the if path .use a small coil form and a variable cap
,tune it with grid dipper before you install it.. This circuit should
be a sharp trap and can easily be tuned to the interfering frequency to
remove the culprit..This may not be top notch engineering,but, it
always works for me..We used to call it a suckout trap... GL W4PQW

If no other fix comes along ,do this ;connect a series resonant =
circuit
to ground in the if path .use a small coil form and a variable cap
,tune it with grid dipper before you install it.. This circuit should
be a sharp trap and can easily be tuned to the interfering frequency =
to
remove the culprit..This may not be top notch engineering,but, it
always works for me..We used to call it a suckout trap... GL W4PQW

Hi Randy,

sorry for my late reply, but I have been out of town.

Thanks for the advice, and you suggestion is just what I am going to do =
next.

As a matter of fact, by making some measurements, it was easy to =
determine what the problem is.

As expected, on 80 and 40 meters I measured the conversion oscillator =
frequency to be 1,650 kHz (i.e. the IF value) higher than the receive =
frequency, .

Conversely, on 10, 15 and 20 meters, the frequency meter indicated that =
the oscillator fundamental frequency runs at HALF the figure one would =
expect. For instance, when the receiver dial is at 14.000 kHz, the =
oscillator runs at 7,825 kHz and the converter tube then works on its =
second harmonic at 15,650 kHz (equal to 14,000 + 1,650). Measuring the =
oscillator waveform period with an oscilloscope, it was easy to confirm =
that the fundamental is at 7,825 kHz. The waveform is not sinusoidal and =
then has a rich harmonics content.

This is just the Hallicrafters design approach, not a problem of my =
receiver. Probably they found it easier to build a high-stability =
oscillator at a lower frequency and exploit the second harmonic.

But, with the oscillator fundamental at 7,825 kHz, the receiver will =
receive both 14,000 kHz and, even better, 9,475 kHz, unless the RF stage =
provides a sufficient block for the latter frequency. =20

Unfortunately, in Europe we have terrific BC signals in the 9.5-MHz =
range, that pass through the receiver RF stage tuned coils, =
independently of the frequency they are tuned at. Problem is that their =
ultimate rejection is too low, and peaking the preselector does not help =
at all.

73

Tony, I0JX