I installed a new piece of shielded cable, both ends grounded, from the mic connector to the first mic audio stage and moved the .001 cap to the tube end where the leads could be much shorter.? Also found that the audio cable running to the mic level control that didn't have that end grounded originally was, but with a poor solder joint that broke at some point.? Fixed that and now the noise level seems to be reduced.? But is still ugly around 40-45 dB down from the peak of a single 1 KHz tone.? No idea what a very good HT-44 looks like in that respect - maybe I'm chasing my tail?


73, Floyd - K8AC

Having developed a fairly easy method for restuffing my OWN can caps, I
prefer them.? Hayseed produces a very workable product, but the
terminals aren't always oriented in the same pattern or position... when
the wiring is short, this makes problems. Just sayin'

Tom - W?EAJ
_._,_._,_

Thanks all for the detailed replies, it is wonderful to hear from S-20R
veterans that have "been there and done that".

Some more details on my skill background to help tailor your advice.? I
am fully equipped with soldering tools, a VOM (1M input impedance I
believe), a 200 MHz Siglent oscilloscope (also 1M impedance), and
various signal generators (NanoVNA for CW waveform, TinySA Ultra for
/modulated/ waveforms like AM, FM, SSB etc), as well as an assortment of
SDRs for receiving signals.

On 04/16/2024 1:58 PM EDT Scott Petersen <s-petersen@...> wrote:

?

?

Most of the tubes in that radio will get warm when the radio is on for more than 10 minutes, and that is a good indication if the filament is good, recapping should be done first, as damage can be done if you run it too long with bad caps. Add a line fuse when you work on it, to protect the power transformer and speaker

?

---

From: [email protected] <[email protected]> on behalf of Bruce KX4AZ <bruce@...>
Sent: Tuesday, April 16, 2024 1:50 PM
To: [email protected] <[email protected]>
Subject: Re: [HallicraftersRadios] S20R project

?

Thanks all for the detailed replies, it is wonderful to hear from S-20R veterans that have "been there and done that".

Some more details on my skill background to help tailor your advice.? I am fully equipped with soldering tools, a VOM (1M input impedance I believe), a 200 MHz Siglent oscilloscope (also 1M impedance), and various signal generators (NanoVNA for CW waveform, TinySA Ultra for modulated waveforms like AM, FM, SSB etc), as well as an assortment of SDRs for receiving signals.

The seller advertised it would plug in and light up, so I did that step before viewing the "innards" condition.? Mechanically I am fine with basic clipping/soldering on wires, but do fall rather flat when it comes to building (cutting metal openings, mounting with nuts/bolts).? But it seems like cap replacement is within my skill set, and I should able to check all the tube filaments with the VOM too.

Bruce

Tell us about yourself.? What is your electronics skill level?? What test equipment is available?? Hand tools, soldering iron, tube tester, test meter and such.? Have you mastered the skill of soldering?? Can you read a schematic?? I am sure that we as a group can guide you through the repair process even if you are a beginner.

I personally would not apply power until I have had a look under the hood, so to speak.? All filter, coupling and bypass capacitors are suspect and should be considered bad and in need of replacement.? As Richard said, if the resistors checked are within 20% then I would think that they are good enough.? There is an octal socket on the rear apron.? There should be a plug installed with two jumpers, is that there?

About the switch problems.? I have found that the dollar store can of penetrating oil spray will do wonders on switches and volume controls.? Just spray and operate the control a few dozen times to work the fluid into the switch / pot.? You can verify operation with your VOM.

Regards,

Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy

On Tuesday, April 16, 2024 at 08:36:45 AM CDT, Richard Knoppow <1oldlens1@...> wrote:

You will definitely have to remove the bottom cover. Simple, a few
screws. The S20R is a straight forward receiver and not difficult to
work on. When restored they are quite good performers and worth the
trouble.
What instruments do you have? To start out you must have a VOM
(Volt-Ohm-Milliamp) meter. Even a very simple one will do. Perfectly
adequate meters are available at places like Harbor Tools for around
$15.00. Without one you can't do very much.
I also suggest looking at tubebooks.org at books on trouble shooting.
A couple of first suggestions: look at the rec/send switch to see if
its working. Use the ohm meter first. Secondly, check the switch in the
headphone jack. If its not connecting the speaker you won't hear
anything. Plugging into the jack a few times may clear the contact. Note
that the headphones are connected to the audio driver stage so the
phones must be high impedance to hear anything there. Old fashioned
magnetic phones, of the sort used for crystal radios, are required.
Do measure the resistance of the tube filaments. That will at least
eliminate any complete duds but burned out filaments are actually quite
rare.
Once you have a VOM do the socket resistance checks. A variation of
20% is normal. It is helpful to follow the schematic when doing the
measurements so you know what you are measuring. In some places there
may be capacitors involved so that the measurements will change with
time and perhaps polarity without indicating anything wrong.
Then do the socket voltage checks. This requires removing the bottom
cover. If you are not used to vacuum tube gear watch your fingers, you
can get quite painful shocks.
For general trouble shooting always begin with the power supply. If
the power supply is not working nothing else will work.
Again, in general, begin at one end and work toward the other, from
input to output, or sometimes the other way. Do ONE thing at a time so
you know what has changed.
Thoroughly clean all the switches before you begin. Evidently the
power switch gave up since it appears to have been bypassed. This is on
the tone control switch and is an add-on type switch. I had to replace
the switch on my S-40A, which is almost identical to the S-20R. It may
be the Send/receive switch is also kaput, look at its terminals with the
ohm meter to see if its working. This is a plain Jane toggle switch so
will be relatively easy to replace.
All the tubes in the S-20R were originally metal except for the
rectifier. There are glass (GT) versions of all of them but the metal
ones provide some additional shielding. If your tubes turn out to be
good just leave them.
All the paper and electrolytic caps will have to be replaced. An
original can type filter cap is available from Hayseed Hamfest. He may
also have a kit of other caps. Modern plastic caps will much improve the
performance of the receiver. There is one low inductance cap in the RF
section, has a woven lead at one end. Just replace it with a modern
plastic cap, they have much lower parasitic reactance than the original
paper caps.
You will have to go over the resistors. Carbon composition
resistors invariably increase in value with time. You will probably find
that all resistors with values of 50K and above are way out of
tolerance. Modern carbon film resistors are better than the old ones
when new and will last forever. Probably any resistor with value within
20% can be left in place.
Since most S-20R receivers were built in war time or shortly
afterward you may find some "bult up" resistors consisting of paralleled
resistors where the right value was not available.
Note that the original speaker is electrodynamic, that is, the
magnet is an electromagnet and acts as a choke for the power supply.
Mostly they are still good. If the speaker does have to be replaced for
some reason a permanent magnet speaker can be used with the field coil
replaced with a 1000 ohm about 5 Watt wire wound resistor. See the
S-40A, which is nearly identical, to see how this is done.
In my S-20R I replaced the detector and noise limiter with the
circuit from the S-40A but the original works OK.
If you have questions I will try to answer them plus you will get a
lot of help from others on this list.
There is an old book "Modern Radio Servicing" by Girardi (not sure
of the spelling) which is helpful, I think its at tubebooks.org
Good luck, neat receivers.

On 4/16/2024 4:39 AM, Bruce KX4AZ wrote:

On Sat, Mar 30, 2024 at 09:19 AM, Bruce KX4AZ wrote:

....decided to take a chance on an Ebay sale of an "as is" unit.
The cosmetic appearance didn't look too bad, and the fact that it
powers on with at least /a /hiss?in the speaker, /and/ that it was
part of a ham estate,? gave me just enough hope to make an offer
that was accepted.? But once I have it in hand I will need to lean
heavily on the S20R experts here, since I have limited skills
(truthfully, ZERO) with regard to troubleshooting and/or restoring
tube radios of this type.

An update on this, I received the S20R boat anchor last week, and I was
encouraged by the above average cosmetic appearance of the cabinet, and
the fact that the power cord had previously been replaced.? The unit
powers on as soon as plugged in (power switch bypassed?), with dial
lights and tube filaments illuminated....at least the tubes with a glass
enclosure.? But there is absolutely nothing detectable from the speaker,
not even a hiss of any kind.? I have the schematic and service manuals
in hand...but I am pondering what the next most logical steps might be.
I am thinking that would be to open the chassis cover to see if any of
the caps etc have already been replaced.? Would checking for the
presence of B+ voltage be another key step? And I suppose checking the
filaments on the non-glass tubes would make sense too.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

On Sat, Mar 30, 2024 at 09:19 AM, Bruce KX4AZ wrote:

....decided to take a chance on an Ebay sale of an "as is" unit.
The cosmetic appearance didn't look too bad, and the fact that it
powers on with at least /a /hiss?in the speaker, /and/ that it was
part of a ham estate,? gave me just enough hope to make an offer
that was accepted.? But once I have it in hand I will need to lean
heavily on the S20R experts here, since I have limited skills
(truthfully, ZERO) with regard to troubleshooting and/or restoring
tube radios of this type.

An update on this, I received the S20R boat anchor last week, and I was
encouraged by the above average cosmetic appearance of the cabinet, and
the fact that the power cord had previously been replaced.? The unit
powers on as soon as plugged in (power switch bypassed?), with dial
lights and tube filaments illuminated....at least the tubes with a glass
enclosure.? But there is absolutely nothing detectable from the speaker,
not even a hiss of any kind.? I have the schematic and service manuals
in hand...but I am pondering what the next most logical steps might be.
I am thinking that would be to open the chassis cover to see if any of
the caps etc have already been replaced.? Would checking for the
presence of B+ voltage be another key step? And I suppose checking the
filaments on the non-glass tubes would make sense too.

On Sat, Mar 30, 2024 at 09:19 AM, Bruce KX4AZ wrote:

....decided to take a chance on an Ebay sale of an "as is" unit.
The cosmetic appearance didn't look too bad, and the fact that it
powers on with at least /a /hiss?in the speaker, /and/ that it was
part of a ham estate,? gave me just enough hope to make an offer
that was accepted.? But once I have it in hand I will need to lean
heavily on the S20R experts here, since I have limited skills
(truthfully, ZERO) with regard to troubleshooting and/or restoring
tube radios of this type.

An update on this, I received the S20R boat anchor last week, and I was
encouraged by the above average cosmetic appearance of the cabinet, and
the fact that the power cord had previously been replaced.? The unit
powers on as soon as plugged in (power switch bypassed?), with dial
lights and tube filaments illuminated....at least the tubes with a glass
enclosure.? But there is absolutely nothing detectable from the speaker,
not even a hiss of any kind.? I have the schematic and service manuals
in hand...but I am pondering what the next most logical steps might be.
I am thinking that would be to open the chassis cover to see if any of
the caps etc have already been replaced.? Would checking for the
presence of B+ voltage be another key step? And I suppose checking the
filaments on the non-glass tubes would make sense too.

On Apr 14, 2024, at 6:45?PM, Leon Robinson via groups.io <leon-robinson@...> wrote:

?

Tony,

A few years ago I had a National NC-109 with an open audio transformer.? I didn't have any audio transformers but I did have a 6.3 Volt filament transformer, I did some calculations and found that the Impedance ratio were almost exactly the same.

I installed it and it worked perfectly.

Leon Robinson ?? K5JLR

Political Correctness is a Political Disease.

Politicians and Diapers should be changed
often and for the same reasons.

On Friday, April 12, 2024 at 05:21:39 AM CDT, Tony Lunsford <tony@...> wrote:

Hello everyone, I’m in the process of getting a SX-140 back on the air. If anyone has an audio output transformer (T4) that you would like to sell, I would really appreciate it. Thanks. ?Tony N5DIM?