[Boatanchors] Mixer alignment problem

[Gerry Steffens]

I have come across a problem a number of times over the many years.  It
appears to be a problem on the lower price tiers of radios.  I have =
observed
it in Hallicrafters S-38E, S-120, S-108 (and maybe on S-85) radios among
others.

When doing an alignment, usually on the high frequency band only but I =
think
I have seen it on the third band occasionally, having completed =
oscillator
alignment successfully, I have found that when peaking the mixer section =
on
the high end of the band, the oscillator appears to be pulled by the
adjustment of the mixer trimmer causing detuning or incorrect =
calibration of
the band.

I have never pursued this problem further before but have kind of taken =
on
the challenge this time.  So far no real successes.  I suspect some =
stray
coupling somewhere but where or what?

Any ideas would be appreciated and anyone else experienced this problem?

Thanks & Cheers from Minnesota,=20

Gerry


Collecting & Restoring E.H. Scott,=20
McMurdo Silver, Hallicrafters, Zenith=20
Transoceanic and any other interesting=20
radios since the 1960s

Gerald Steffens P.E.
Oronoco, MN


Over 300 "Boatanchors" salvaged.
Collection approaching 300 radios, 2 Oldsmobiles and a 1950 GMC.