"ablebravo" wrote in message
ups.com...
this is the first more complex (than s38s) halli have i
tried to
repair. as received, the set. set played, but w/out
sensitivity or
vol. recapped (not micas) and tested all tubes, replacing
as needed.
checked resistors, and replaced a few. set also had
severe crackling
which matched 'short in a tuning cap' as described in
marcus and levy.
i replaced the tuning condensor, due to remaining crackles
i simply
couldn't get out w/cleaning. crackles went away
w/partswap and set
appeared to align well -- used scope across output to
voice coil. got
good volume and nice waves as i went thru the IF and the
band steps.
for IF the sig gen was connected to the center of the
gang, the middle
of 3 posts on the top of it, w/the ground to the chassis
and the gang
fully open.

radio plays well on band 3 -- good vol on strong station,
many stations
w/short wire. picks up similarly on band 2 down to about
4 mhz.

bc is silent except for what sounds like a couple of spots
that 'want
to be' stations. very faint voice heard in one spot.
band 4 seems to
be similar.

a quick reattach of sig gen, and good tones heard all
bands at align
freq for those bands, and good IF tone. bandswitch was
checked and
cleaned. seems to be making good contact w/clean
click/pop as changed
w/set on. a little puzzled where to look because of this.

docs say make sure the image freq is out of the way of
oscillator freq
for bands. i don't quite understand what this means, or
how to be sure
they aren't colliding, but i think i may have misaligned
the base IF?
maybe aligned with an image of it? have noticed when
aligning other
sets, you can find several positions that ring w/the tone,
but only one
that rings best. is this the result of getting the echo
instead of the
original? care was taken on the rf aligns to find thru
most of the adj
range for the best response. but did not try moving the
if's
radically.
ab

This last means to make sure the local oscillator is on
the correct side of the signal, that is, make sure you are
not peaking up the image of the desired signal. This is most
likely on the top band (band 4) since image suppression will
probably be adequate to prevent it on the lower bands. The
oscillator of the S-40 and S-40-A is above the signal
frequency on bands 1,2,and 3, and below it on band 4. If you
have the oscillator on the wrong side of the signal the
sensitivity will be low and the frequency calibration off.
You can measure the oscillator frequency with another radio
with similar frequency range, just pick up its radiation on
the the receiver. You don't need anyhing too accurate, just
enough to tell within 455khz of where the oscillator is.
This problem is very unlikely on the BC band but might well
be the problem on band 4. Another receiver will also tell
you if the oscillator is weak or cutting out at some points
on the band.
Since you know the IF stages work OK the problem is
isolated to the RF or Mixer stages. You can probably check
the mixer by injecting a signal directly into it. Probably a
wire wound around the tube (with shield off) a few times
will get enough signal into it. It won't be as sensitive as
normal but should give you some response. If this seems to
work OK the problem is in the RF amp.
Someone suggested one or more antenna primary coils may
be open. This is possible and does not have to be damage
from lightning. Its easy to check, just put an ohm meter
across the two antenna terminals on the back of the set
(with the ground link open) and measure the resistance. It
will vary with the band but should be pretty low for all. If
the coil is open you will get an open circuit indication on
the ohm meter. Sometimes all that happens is that the solder
connections at the ends of the coil have opened up. Often
just heating them with a little extra solder will fix the
coil. Lightning damage is usually pretty extreme and easy to
spot.
It sounds like you have a service manual. You might check
the manuals available on the BAMA site, there are several
covering the S-40 and S-40A. While there are differences the
two are enough alike so that the rather complete technical
manual for the S-40 may be of some help. I would download
everything there that pertains to this receiver, there may
be a hint in one that is missed in the others.
BTW, I am surprized that it was necessary to replace the
tuning capacitor. Variable capacitors are usually noisy due
to dirt between the plates or intermittant ground
connections to the rotor. Lubricating the bearings with a
tuner lubricant may also help. Make sure the replacement
capacitor isn't going open at some points.
See if any of this helps. You can also contact me via
e-mail if you want. The first time you will get a spam
blocker message. I will also follow this thread in this
group and respond here if you prefer.
Good luck in restoring this thing, its a neat little
receiver.


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Richard Knoppow
Los Angeles, CA, USA