[NJARC] Philco 37-650 RF Question

[Scott Roberts]

--- Al Klase <skywaves at webex.net> wrote:

> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Hi Scott,
> 
> We may have to take this a step at a time.  If I had
> to guess, I'd say 
> there is a problem, possibly an open connection ,
> with trimmer cap "16A" 
> the BC-band oscillator padder, a.k.a  "compensator",
> capacitor.   If 
> this cap is not in the circuit the oscillator will
> not be able to tune 
> the low end of the band.
> 
> What test equipment do you have?  An oscilloscope or
> frequency counter 
> would allow you to observe the behavior of the
> oscillator.  
> Alternatively, if you have a communication receiver
> with a BFO you can 
> listen for the oscillator as if it were a CW signal.
>  When working 
> properly, the oscillator will be 470KHz above the
> tuned frequency.
> 
> Regarding AVC: See RECOGNIZING AND DEALING WITH AVC
> PROBLEMS
> in the "Communications Receivers" -> "Maintenance"
> page of my website
> 
>
http://www.skywaves.ar88.net/commrx/Maintenance/agc.htm
> 
> Regards,
> Al
> 
> 
> Scott Roberts wrote:
> 
> >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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> >
> >
> >  
> >
> 
> -- 
> Al Klase - N3FRQ
> Flemington, NJ
> http://www.skywaves.ar88.net/
> 
> 
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