I wrote a short time ago about the apparently reversed
band spread capacotor in my S-40A. Here is a bit more.
First, for those who did not see the original thread, I
found the band spread cap in my RX had the stop pin mounted
in such a way that when the plates were rotated in the
direction that normal dial string threading gave they went
backwards. That is, the BS dial was at 100 at minimum
capacitance. This is the reverse of normal Hallicrafters
practice and does not match the dial, which indicates
dial-set at 0. It was possible to get the capacitor, dial,
and knob to run in the correct direction by crossing over
the dial string at the capacitor drive pulley. I thought the
pin had been removed and replaced by someone who wanted the
BS dial to run from 100 as the BS does in most other makes
of RX (but not Hallicrafters).
With the help of Jeffrey Angus I was able to remove the
pin (actually he did it) and replaced it with a roll pin
facing the right way.
When I went to restring the dial drive I realized that
the diagram in the Hallicrafters handbook _and_ in the
Rider's sheets was wrong, in fact, the stringing must be
done in reverse of what is shown. I then discovered that the
stringing information for the S-40 is more nearly what I
had. Note that in the two sets of diagrams the capacitor
pulley is shown facing in opposite directions. For the S-40
the opening in the flange is shown facing up and in the
S-40A its facing down. In my S-40A it appears that the
pulley itself was reversed when swaged on. This would match
the reversed pin position. From the photos I've found on the
web the type of band spread rotor is different in the S-40
and S-40A. The S-40 appears to have a single rotor plate for
each section which is straight line frequency shaped (kidney
bean shaped), and two stator plates, this is similar to the
cap in the S-20R, which was the predecessor of the S-40
series. The S-40A has two plates on each rotor section and a
single plate as a stator. The S-40B appears from the photos
to have reverted to the single rotor plate type used in the
earlier receivers.
I am beginning to suspect that H my have gotten a lot
of defective tuning capacitors and used them by reversing
the dial stringing as I had to. My S-40A appears from
various evidence to be an early one, probably made in the
first run or in the first year of manufacture. One clue is
the lack of a filament dropping resistor on the 6H6
noise-limiter and gas gate diode. This is absent in the
Rider's sheets on the web, which are dated February, 1948,
but is present in the Hallicrafter's Service Bulletin dated
November, 1948. The latter indicates it is for Run No.3. My
RX has an inspection stamp indicating Run No.1.
At about this time parts were still in short supply and
there was still some instability in the electronics
industry, which was still recovering from WW-2. That makes
me think that the explanation of the cap being defective may
be correct. There may have been production deadlines to meet
or financial considerations that prevented rejection of the
parts. Its also possible that some got mounted on chassis
before any error was discovered.
In any case, it would be useful if others owning S-40A
receivers would take a look at the capacitor in theirs and
report what they find.
In one web site with some H history on it its stated
that all of H's business records were destroyed by the
Wilcox Electric Co. when they took H over. Too bad since
they would probably have held the answer to this, and
probably a great many other mysteries.

I also want to thank all those in this group who have
been so helpful with this, and other, projects.


--

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Richard Knoppow
Los Angeles
WB6KBL

On Thu, 02 Apr 2009 10:52:03 -0700, Richard Knoppow wrote:

[snip]

I am beginning to suspect that H my have gotten a lot
of defective tuning capacitors and used them by reversing the dial
stringing as I had to.


Just to continue with the speculation, it's conceivable that
Hallicrafters got exactly the tuning caps they wanted. A reverse
rotation bandspread cap works well enough in the S-40A and the reverse
rotation cap might have been necessary in some planned S-40 variant.

[snip]


? My S-40A appears from various evidence to be an
early one, probably made in the first run or in the first year of
manufacture. One clue is the lack of a filament dropping resistor on the
6H6 noise-limiter and gas gate diode. This is absent in the Rider's
sheets on the web, which are dated February, 1948, but is present in the
Hallicrafter's Service Bulletin dated November, 1948. The latter
indicates it is for Run No.3. My RX has an inspection stamp indicating
Run No.1.

My S-40A has the reverse rotation cap. If I recall correctly, it has the
6H6 resistor.

I can't check it out right now, but I should be able to within a couple
of weeks.

Frank Dresser

"Frank Dresser" wrote in
message ...
On Thu, 02 Apr 2009 10:52:03 -0700, Richard Knoppow wrote:

[snip]

I am beginning to suspect that H my have gotten a
lot
of defective tuning capacitors and used them by reversing
the dial
stringing as I had to.


Just to continue with the speculation, it's conceivable
that
Hallicrafters got exactly the tuning caps they wanted. A
reverse
rotation bandspread cap works well enough in the S-40A and
the reverse
rotation cap might have been necessary in some planned
S-40 variant.

[snip]

I don't think so. The knob, dial, and capacitor should
all rotate in the same direction. The dial must start at
zero beacuse that's the marked "band set" point, the
capacitor must set at minimum capacitance for the main dial
calibration to operate within the adjustment range of the
trimmer caps. The S-40A band spread capacitor differes from
the one used in the other S-40 models and in the S-20R,
which was the predecessor to the S-40 series, in that its
got symmerical band spread plates, the others have straight
line frequency plates. This means the rotor could rotate in
either direction and still have the same "law" of
capacitance variation with angle. The others _must_ turn in
one direction only. One of the things I noticed is that the
poistion of the opening in the flange of the main pulley as
shown in the stringing diagrams is reversed in the S-40A
from the position shown in the S-40 diagram. Usually,
stringing diagrams are shown for the dial being at one end
so that when you wind on the dial cord you have the stop to
work against. This is not the case in my RX. So, I think
both the stop pin _and_ the pulley were put on wrong. One
can speculate about why this was done. You may be right that
H specified these caps for some variation of the RX but
never made it. But, keep on mind that parts were evidently
in short supply when the RX was made so perhaps the caps
were used and the dial string crossed over as a work-around.
Note that one of the power resistors was made up of two
resistors in parallel, this is mentioned in the parts list
as a possibility so I am pretty sure it came from the
factory. It suggests that H could not get enough of some
parts and had to resort to work-arounds to meet production
committments.
Again, apparently all Hallicrafters business records
were long ago destroyed so one can only guess. If someone
has an original insruction manual the photos may be clear
enough to see how the cap is rigged, the stuff on line is
too low in resolution to show this. I wanted others with
S-40's of various types and vintages to have a look at what
is actually in them. What I am curious about can be seen by
just lifting the lid and seeing in wich direction the band
spread cap moves in going from minimum to maximum.
This is all probably quite trivial in the scheme of
things but sometimes its the seemingly trivial things which
are the most interesting:-)


--

--
Richard Knoppow
Los Angeles
WB6KBL