I've begun the restoration of an S-38B. Just started to replace the filters
an I already have a question. The old multi-section cap ground is connected
to pin 2 of the 35Z5 rather than directly to the chassis ground as shown in
the schematic he
http://i1206.photobucket.com/albums/...gFilterCap.png
Pin2 is connected to the chassis ground through the filament string, which
has a 125 ohm resistance when cold. Is this a problem or were all S38's
wired in this manner?

The filter cap appears to be original but you can't always be certain. It's
clear other repairs have been made during its lifetime.

If anyone can recall recapping an S-38 I'd be interested in your observation
regarding the filter cap ground wire location.

Thanks,

DaveW

First, I don't have an answer, but am preparing to recap an even older S-38
myself. I think I remember
from many, many years ago, that some of those "hot chassis" rigs had two
ground systems, that were actually connected together at some point.
Something about "ground loops" and hum
reduction. In the schematic you linked here, there are two different ground
symbols. Could one be the actual chassis connection, and the other sort of a
slightly "lifted" or signal/RF ground? Just guessing, hope someone knows the
real answer!

Old Chief Lynn, W7LTQ


"DaveW" wrote in message
...
I've begun the restoration of an S-38B. Just started to replace the
filters an I already have a question. The old multi-section cap ground is
connected to pin 2 of the 35Z5 rather than directly to the chassis ground
as shown in the schematic he
http://i1206.photobucket.com/albums/...gFilterCap.png
Pin2 is connected to the chassis ground through the filament string, which
has a 125 ohm resistance when cold. Is this a problem or were all S38's
wired in this manner?

The filter cap appears to be original but you can't always be certain.
It's clear other repairs have been made during its lifetime.

If anyone can recall recapping an S-38 I'd be interested in your
observation regarding the filter cap ground wire location.

Thanks,

DaveW

I checked the schematic notes and the inverted pyramid symbol is the chassis
ground. The other symbol is the cabinet ground. Apparently the chassis is
isolated from the cabinet except for a single 0.25 mfd capacitor which
connects the two.

DaveW


"coffelt2" wrote in message
...
First, I don't have an answer, but am preparing to recap an even older
S-38 myself. I think I remember
from many, many years ago, that some of those "hot chassis" rigs had two
ground systems, that were actually connected together at some point.
Something about "ground loops" and hum
reduction. In the schematic you linked here, there are two different
ground symbols. Could one be the actual chassis connection, and the other
sort of a slightly "lifted" or signal/RF ground? Just guessing, hope
someone knows the real answer!

Old Chief Lynn, W7LTQ


"DaveW" wrote in message
...
I've begun the restoration of an S-38B. Just started to replace the
filters an I already have a question. The old multi-section cap ground
is connected to pin 2 of the 35Z5 rather than directly to the chassis
ground as shown in the schematic he
http://i1206.photobucket.com/albums/...gFilterCap.png
Pin2 is connected to the chassis ground through the filament string,
which has a 125 ohm resistance when cold. Is this a problem or were all
S38's wired in this manner?

The filter cap appears to be original but you can't always be certain.
It's clear other repairs have been made during its lifetime.

If anyone can recall recapping an S-38 I'd be interested in your
observation regarding the filter cap ground wire location.

Thanks,

DaveW

Yikes! That's why you could get quite a jolt just from the cabinet, and it
wasn't too cool
to use the S-38 right next to a grounded piece of gear. I think I remember
something in
QST "Hints and Kinks" about putting a light bulb (small wattage) between the
S-38's cabinet
and an adjacent, grounded piece of gear. If the lamp illuminated, reverse
the S-38's AC
wall plug.

Old Chief Lynn, W7LTQ


"DaveW" wrote in message
...
I checked the schematic notes and the inverted pyramid symbol is the
chassis ground. The other symbol is the cabinet ground. Apparently the
chassis is isolated from the cabinet except for a single 0.25 mfd capacitor
which connects the two.

DaveW


"coffelt2" wrote in message
...
First, I don't have an answer, but am preparing to recap an even older
S-38 myself. I think I remember
from many, many years ago, that some of those "hot chassis" rigs had two
ground systems, that were actually connected together at some point.
Something about "ground loops" and hum
reduction. In the schematic you linked here, there are two different
ground symbols. Could one be the actual chassis connection, and the other
sort of a slightly "lifted" or signal/RF ground? Just guessing, hope
someone knows the real answer!

Old Chief Lynn, W7LTQ


"DaveW" wrote in message
...
I've begun the restoration of an S-38B. Just started to replace the
filters an I already have a question. The old multi-section cap ground
is connected to pin 2 of the 35Z5 rather than directly to the chassis
ground as shown in the schematic he
http://i1206.photobucket.com/albums/...gFilterCap.png
Pin2 is connected to the chassis ground through the filament string,
which has a 125 ohm resistance when cold. Is this a problem or were all
S38's wired in this manner?

The filter cap appears to be original but you can't always be certain.
It's clear other repairs have been made during its lifetime.

If anyone can recall recapping an S-38 I'd be interested in your
observation regarding the filter cap ground wire location.

Thanks,

DaveW

coffelt2 wrote:
Yikes! That's why you could get quite a jolt just from the cabinet, and it
wasn't too cool
to use the S-38 right next to a grounded piece of gear. I think I remember
something in
QST "Hints and Kinks" about putting a light bulb (small wattage) between the
S-38's cabinet
and an adjacent, grounded piece of gear. If the lamp illuminated, reverse
the S-38's AC
wall plug.

Back in my mispent youth, I took an S-38B which I had been given, and stuffed
a small 120v output AC transformer in it to use as an isolation transformer.

I also added a little bit of 1960's technology to it, I put two silicon diodes
in as a noise limiter.

In a fit of cleaning out, having long since gotten digital showrtwave radios,
in the 1980's I gave the radio away.

Geoff.
--
Geoffrey S. Mendelson, N3OWJ/4X1GM
My high blood pressure medicine reduces my midichlorian count. :-(

On Sun, 11 Mar 2012, Geoffrey S. Mendelson wrote:

coffelt2 wrote:
Yikes! That's why you could get quite a jolt just from the cabinet, and it
wasn't too cool
to use the S-38 right next to a grounded piece of gear. I think I remember
something in
QST "Hints and Kinks" about putting a light bulb (small wattage) between the
S-38's cabinet
and an adjacent, grounded piece of gear. If the lamp illuminated, reverse
the S-38's AC
wall plug.

Back in my mispent youth, I took an S-38B which I had been given, and stuffed
a small 120v output AC transformer in it to use as an isolation transformer.

I also added a little bit of 1960's technology to it, I put two silicon diodes
in as a noise limiter.

In a fit of cleaning out, having long since gotten digital showrtwave radios,
in the 1980's I gave the radio away.

There was a story in "73" in the mid-sixties about someone trading in his
S38 for a better receiver (and obviously cash needed too). So the story
is basically about all the modifications he had to undo to put it back to
"normal". And right when he's at the store, he realizes he's forgotten
one mod, so he takes that out in the parking lot, I seem to recall having
to do some makeshift arrangement to cover the extra hole from that mod.

The isolation transformer wouldn't improve the receiver's ability to
receive one bit, but it sure made it a lot safer to use.

Michael

On Sat, 10 Mar 2012 21:28:25 -0600, DaveW wrote:

I've begun the restoration of an S-38B. Just started to replace the
filters an I already have a question. The old multi-section cap ground
is connected to pin 2 of the 35Z5 rather than directly to the chassis
ground as shown in the schematic he
http://i1206.photobucket.com/albums/...watcher32/S38-
BFilamentStringFilterCap.png
Pin2 is connected to the chassis ground through the filament string,
which has a 125 ohm resistance when cold. Is this a problem or were all
S38's wired in this manner?

The filter cap appears to be original but you can't always be certain.
It's clear other repairs have been made during its lifetime.

If anyone can recall recapping an S-38 I'd be interested in your
observation regarding the filter cap ground wire location.

Thanks,

DaveW

I have never worked on an S-38 but I don't see how it could work wired
the way you described. Perhaps someone botched a recap job, couldn't
figure out why a new capacitor caused hum as bad or worse than the old
cap, and put it away for some future troubleshooting.

Are you sure you counted the pins correctly and that you are, indeed,
looking at the 35Z5 socket?

I checked a tube manual and your schematic shows the correct connections
for a 35Z5. The physical location of the capacitor's negative lead
should be where the wire from the switch connects to the chassis although
some other places are likely to work as well. The idea is to keep the
ripple current flowing through the capacitor from getting into other
circuits. The chassis has resistance and inductance and this current
causes voltage drops that can inject hum into sensitive circuits.

As others have mentioned, it's not the safest way to design a radio, but
it did work.

Good luck,

--
Jim Mueller

To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.

Just last week, I came across one for sale near Pittsburgh.
The owner bought it for $3.00 and was trying to sell it for $100.00

Before I approached him, I informed him about the floating ground issue and how the radio was dangerous and how it needed a transformer to make it more safe - due to the fact that it was designed for use with 120 VDC current not AC...

I could have bought it for $25.00 - but was unwilling to drive 120 miles to go pick it up.
When I stopped by a couple of days later - he had already sold it.

The radio is of little value - since it only did CW AM and has no SSB....
Just looking on Flea Bay tells me that they had issues with the cardboard on the rear of the radio - lot's of reproductions.

It would be ok if all you wanted it for was to listen to local traffic on the 11 meters - since it is mostly AM anyways!

With all this discussion on the S 38 series, I wonder if everyone
knows about the S 38 website? http://www.the-s38-guy.com/ He has
some great information and hints. 73 Mike KF6KXG

"Channel Jumper" wrote in message
...
Just last week, I came across one for sale near Pittsburgh.
The owner bought it for $3.00 and was trying to sell it for $100.00

Before I approached him, I informed him about the floating ground issue
and how the radio was dangerous and how it needed a transformer to make
it more safe - due to the fact that it was designed for use with 120 VDC
current not AC...

I could have bought it for $25.00 - but was unwilling to drive 120 miles
to go pick it up.
When I stopped by a couple of days later - he had already sold it.

The radio is of little value - since it only did CW AM and has no
SSB....
Just looking on Flea Bay tells me that they had issues with the
cardboard on the rear of the radio - lot's of reproductions.

It would be ok if all you wanted it for was to listen to local traffic
on the 11 meters - since it is mostly AM anyways!

Channel Jumper

.......and thus fully qualifies as a genuine BOATANCHOR!

Old Chief Lynn, W7LTQ (Let's hear it for the old S-38 !!!!!!!!!!!!!!)