Today I bought an S-20-R which appeared to be in very
good condition. However, someone replaced the original
speaker. The problem is that the original is a field coil
type where the coil is also the power supply filter choke. I
can probably find a suitable choke but would prefer, if
possible, to find an original speaker. One in working
condition is, of course, ideal, but one with a working field
coil and matching transformer is acceptable because I can
almost certainly get it re-coned locally. Other than that
the thing seems to be in good condition and sort of works.
Please respond via personal e-mail. The address below
is on a spam-blocker but I will unblock you. I can also be
reached through the ARRL forwarder in the usual way (my call
@ ARRL.org).
This is an example of total impulse buying:-(



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Richard Knoppow
Los Angeles
WB6KBL

On Dec 27, 6:24*pm, "Richard Knoppow" wrote:
* * *Today I bought an S-20-R which appeared to be in very
good condition. However, someone replaced the original
speaker. The problem is that the original is a field coil
type where the coil is also the power supply filter choke. I
can probably find a suitable choke but would prefer, if
possible, to find an original speaker. One in working
condition is, of course, ideal, but one with a working field
coil and matching transformer is acceptable because I can
almost certainly get it re-coned locally. Other than that
the thing seems to be in good condition and sort of works.
* * *Please respond via personal e-mail. The address below
is on a spam-blocker but I will unblock you. I can also be
reached through the ARRL forwarder in the usual way (my call
@ ARRL.org).
* * *This is an example of total impulse buying:-(

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Well, as I sometimes do, I yelled for help too soon. A bit of
research shows that the later S-40A is nearly identical to the S-20R
and later versions of the S-40 are not much different. All use a
straight RC filter in the power supply with a 1500 ohm resistor in
place of the speaker field (which is also 1500 ohms DC resistance).
That is exactly the way this RX is modified so there does not appear
to be any advantage in trying to find an original speaker assembly.
While I still need to do some detailing on this little guy it seems to
work very well and is surprisingly good sounding.

The speaker FC must have been a weak link. Mine also had
a replacement speaker installed.

"Tio Pedro" wrote in message
...
The speaker FC must have been a weak link. Mine also had
a replacement speaker installed.
You could be right, the S-20R seems to be one of the
last receivers Hallicrafters made using a field coil
speaker. They were common in the 1930's and 1940's because
good permanent magnet materials were just becoming available
and were somewhat expensive and it was an economy to use the
field coil as a smoothing choke.
I am curious about the mounting method originally used.
The advertising states that the speaker was "shock mounted"
probably to avoid microphonics, but, since the original
mounting is gone, I have no idea of how this was done.
Perhaps someone with an intact S-20R or S-22 could have a
look.
Another curiousity: The bottom cover has a series of
holes for access to the adjustments. Around this are four
small holes. It does not appear that anything was ever
screwed to these. I wonder if there was once a cover over
the holes or if, perhaps, there was just nothing ever there.
Another curiousity, I seem to be full of them: On H
receivers the band spread is normally set at zero. On this
RX it will go to about 95 but not all the way to 100, is
this normal for this thing?


--
--
Richard Knoppow
Los Angeles, CA, USA

"Richard Knoppow" wrote in message
...

" .
Another curiousity, I seem to be full of them: On H receivers the band
spread is normally set at zero. On this RX it will go to about 95 but not
all the way to 100, is this normal for this thing?


My silence is due to the fact mine is completely torn
down awaiting a new paint job.

Pete

"Tio Pedro" wrote in message
...

"Richard Knoppow" wrote in
message
...

" .
Another curiousity, I seem to be full of them: On H
receivers the band spread is normally set at zero. On
this RX it will go to about 95 but not all the way to
100, is this normal for this thing?


My silence is due to the fact mine is completely torn
down awaiting a new paint job.

Pete

I have to remove the case from mine in order to try to
polish the band spread window. Its about the only real
blemish on the thing. I've had good luck before in restoring
celuloid using toothpaste. Toothpaste is a good polish where
you want a _very_ mild abrasive.


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Richard Knoppow
Los Angeles
WB6KBL