[NJARC] Philco 37-650 RF Question

Thu Feb 23 18:45:41 EST 2006

I used all carbon composition resistors: I actually
had found one which was a little out of tolerance:
apparently the wrong band color had been missed when
it was shipped, and I didn't check, believing it
correct. (Learned a lesson for next time) Turns out
the resistor was not 330k Ohm, but 3,300Meg ohm...
Just a little high. I replaced it, and got back most
of my BC band at that point, but it continues as
described.

After I first finished the rebuild, I had BC band, and
some SW. It was working, but after a few hours, it
stopped.(This was before I discovered the 3300M
resistor.) I don't know if it is possible the overly
high resistance being pushed through damaged something
else.

Scott

--- Robert Bennett <dino66 at optonline.net> wrote:

> Visit our web site - See http://www.njarc.org
> _______________________________________________
>  Scott -
>                 I had a similar problem with a
> restoration of a 40's Zenith
> console. I couldn't get the BC band to work under
> 1000KC. What I learned was
> that I had replaced some "out of tolerance"
> resistors in the RF section that
> were "carbon film" instead of carbon composition
> (like the originals). A
> fellow enthusiast informed me that the "carbon film"
> or "metal film"
> resistors will not pass current as well. I replaced
> the resistors again and
> Voila! I had the whole BC band again! Since then, I
> only use carbon
> composition resistors in the RF and IF sections.
> Hope you find it!
> 
> Bob Bennett
> ----- Original Message ----- 
> From: "Scott Roberts" <ng19delta at yahoo.com>
> To: "New Jersey Antique Radio Club"
> <njarc at mailman.qth.net>
> Sent: Thursday, February 23, 2006 5:24 PM
> Subject: [NJARC] Philco 37-650 RF Question
> 
> 
> > Visit our web site - See http://www.njarc.org
> > _______________________________________________
> > 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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> 
> 
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