[NJARC] Philco 37-650 RF Question

[Scott Roberts]

Greetings! The story so far: I have a Philco 37-650
which I have been rebuilding for some time now. I've
gotten most of the kinks out, but am still having a
bit of an issue with the BC band. The two SW bands are
operating nicely at this point, and the BC does work,
but only to a particular point.

In rebuilding this radio, all the caps- electrolytic,
paper and mica, as well as bakelite, have been
replaced, or rebuilt with newer replacement parts.
These parts were within the 10% rule of thumb when
original values were not obtainable. Also, the vast
majority of the wiring was replaced, and there are
only a couple sections which were not, for the simple
fact they seemed to be ok. However, in doing so, I
replaced I replaced sections of 20 or 22 gauge solid
wire with 20 gauge stranded. 

My problem is this- The BC band works- between 900 and
1700. Below 900, it is all squeals and sqwauks and
burrs. I have aligned the IF coils as specified in the
tech sheets, and also the antenna, RF and Osc.
sections, for both SW's and BC band. But it seems like
the BC band is "squished"- If I adjust to specs,
nothing in BC is quite where it should be. If I
realign by ear 1210 to the proper dial indication,
then turn to 1060, 1060 is high. Readjusting 1060
moves 1210, and 950. Everything stays above 900, and I
can't get anything below 900. I have fiddled, twisted,
and contemplated to no avail. I have checked and
rechecked the components in the RF subchassis:
switches are clean as I can get them, coils are fine-
even discovered a resistance value issue with leads
I'd replaced, and restored it to correct value.
Everything checks out OK.

It has been suggested that the RF current moves along
the outside of the conductor: and that in replacing
the solid wiring with stranded, I may have disrupted
this flow's proper characteristics. Is this possible,
and would it cause the symptoms I am experiencing?

Any replies appreciated- I'm almost pulling my hair
out with this one. As my first major rebuild of a
radio, it is my learning experience: And it almost
works, except for this issue.

Also, can anybody explain "AVC" to me? In this radio,
the cpncept does not seem to match reality. Louder
stations are LOUD, and quieter ones not, so I get neat
differences when changing, rather than reduced volume
of loud stations, when set for the quiet ones to be
heard.

This radio has a whole group of topics occupied on the
Philco Phorum, and I can send along the link if
desired. Long story short, I haven't gotten a working
solution to the BC problem yet, so I thought I'd bring
it here...

Thanks for any help,
Scott

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