I recently completed restoring a pair of S-40B radios. The original
power transformers were pretty marginal, so I replaced them with similar
transformers that I bought from Antique Electronic Supply (the new
xfrmrs were Fender amp replacements). Everything seemed to work ok for
a couple of weeks of light use of my radio (I gave the other to my father).

Last week while I was listening to my S-40B, its power supply blew a
fuse (a 5A cartridge fuse that I installed in the radio). I traced the
problem back to the "new" power transformer. It appeared to have a
short circuit of some kind, though I could never pin down exactly where
this short was using a DVM.

The initial fuse blow occurred while the radio was running and my
house's central air conditioner was switching on. Up to that first fuse
blow, I noticed some significant flicker in the dial lamps (run off the
filament winding on the power transformer). At first I thought that I
was watching a dying lamp bulb, but now it seems that I was witnessing
the breakdown of the power transformer.

My question is, would installing an inrush current protector thermistor
in the primary winding circuit of this radio prevent a repeat of the
transformer breakdown? If this is a good move, what size of thermistor
should I use? Any help or recommendations would be appreciated.

Steve Burrows

"Steven P. Burrows" wrote in message
news:461mg.57866$9c6.34117@dukeread11...

My question is, would installing an inrush current protector thermistor in
the primary winding circuit of this radio prevent a repeat of the
transformer breakdown? If this is a good move, what size of thermistor
should I use? Any help or recommendations would be appreciated.

Steve Burrows


Steve,

When I was a Novice, I used a S-40B on 80-40-15 meters CW. Boy, 15 meters
CW was a challenge with that primitive receiver! They did a good job with AM
broadcast however, and the audio was decent.

Now the bad news. Maybe your rectifier tube showed a series of bright
sparks leading to the blown fuse? If so, the B+ was being dragged down
somewhere, and likely from a leaky, or shorted capacitor. It's quick and
easy to pull the rectifier (5Y3??) and see if the fuse blows again. A 5
ampere fuse is pretty heavy for a S-40B, so in the future consider a 2 amp
unit. If there was no short, or bad 5Y3, then your new transformer was
likely marginal, and I bet would have failed regardless of what you did.

That said, if large transients come down the power line, you can filter
these out to a point. One option is to add a varistor across the primary
leads of the transformer. These are made by GE and others, and the part
number will be similar to V130LA10A. This means the part is rated for 130
volts RMS AC, and 10 Joule rated. I believe Radio Shack has these.

I don't believe an inrush current limiter is a solution here. These are more
useful when a big light dimming surge occurs when turning on a big Linear
amplifier like the Dentron MLA-2500.

Good luck with that S-40B,
Jim
WD5JKO

On Tue, 20 Jun 2006, Steven P. Burrows wrote:

I recently completed restoring a pair of S-40B radios. The original power
transformers were pretty marginal, so I replaced them with similar
transformers that I bought from Antique Electronic Supply (the new xfrmrs
were Fender amp replacements). Everything seemed to work ok for a couple of
weeks of light use of my radio (I gave the other to my father).

Last week while I was listening to my S-40B, its power supply blew a fuse (a
5A cartridge fuse that I installed in the radio). I traced the problem back
to the "new" power transformer. It appeared to have a short circuit of some
kind, though I could never pin down exactly where this short was using a DVM.

It seems to me highly unlikely that a new power transformer could develop
a short circuit (somewhere in its windings) and you should look for
the exact cause of the fuse blowing. Another response indicated that 5
amps is much higher than you should have, and something more like 2 amps
is better. Is the new transformer a good match to the old one? Does it get
very hot when it is running? Is the plate voltage about right coming out
of the S-40 power supply? When you "traced the problem back to the 'new'
power transformer" what was it that you traced and how?

The initial fuse blow occurred while the radio was running and my house's
central air conditioner was switching on. Up to that first fuse blow, I
noticed some significant flicker in the dial lamps (run off the filament
winding on the power transformer). At first I thought that I was watching a
dying lamp bulb, but now it seems that I was witnessing the breakdown of the
power transformer.

My question is, would installing an inrush current protector thermistor in
the primary winding circuit of this radio prevent a repeat of the transformer
breakdown?

You really should not need to go to this extreme. Think how many millions
of such radios and TV sets and HiFi/stereo sets were used in the last
50-60 years with very very little problems. Only some very rare freak
voltage spike might cause peak voltage on the electrolytic to go past
breakdown and with a vacuum tube rectifier and some capacitance in the
electrolytic, it would have to be a pretty freakish high pulse voltage for
a fairly long time interval to kill whatever sections in the electrolytic
cap would break down for a freak pulse.

Is the receiver still blowing fuses? Is it not working any more, period?

If this is a good move, what size of thermistor should I use?
Any help or recommendations would be appreciated.

Steve Burrows

The B+ voltage delivered by the new transformer is about 50 volts higher
than Hallicrafters' original spec., which I was advised was not a big
problem. The other secondaries for the tube filaments and rectifier
filament were exactly right.

Throughout my use of this restored S-40B, I have been running it off of
a personal computer grade surge suppressor power strip, along with my
other old radios (others are solid state).

I replaced the power supply electrolytic caps with new ones, so I doubt
that this was a problem. From past experience with arcing in the
rectifier tube, I also looked into this possible cause. My rectifier
tube was also OK.

I pulled all of the tubes from the radio and powered it up in a darkened
room to attempt to see any potential arcing under the chassis. The fuse
blew, and there was no visible evidence of any problems in the radio wiring.

Next I disconnected the secondaries of the power transformer from the
radio entirely. The fuse still blew.

Next I removed the safety filter capacitors from the transformer primary
circuits. Fuse still blew. I traced out the primary circuit with a DVM
and found no short circuits in my wiring or from the transformer
windings to each other or to the transformer frame. With the transformer
completely taken out of the radio the fuse blowing stopped. I was
forced to conclude that the "new" transformer was a dud.

I don't have access right now to a variac, but I suspect that there
might be some sort of arcing in the transformer that doesn't show up
until higher voltages are applied. I still have this transformer, and I
might try looking at it again later this year when I can borrow a variac
from the university where I work.

I have replaced the suspect transformer and so far the radio is working
fine. My interest in using inrush current limiters is motivated by
trying to avoid a repeat of a damaged transformer, both in my father's
S-40B or my own.

In spite of having a fancy microprocessor based Sony SW-77 to do my
SWLing on, I find using this old 'boatanchor' type radio irresistible.
After I finish up grad school (which I am starting rather late in life -
age 46) I plan to go for a ham license and possibly look into using
other BA gear.

Steven P. Burrows wrote:
The B+ voltage delivered by the new transformer is about 50 volts higher
than Hallicrafters' original spec., which I was advised was not a big
problem.

That is correct, it is not a big problem, it is a *HUGE* problem.

Most of these older radios were designed for a 115V nominal power line
voltage. Today, people complain if the voltage is as low as 120V at the
outlet. It is more typically 123 to 125V. That means that even using the
original transformer, you will have nearly a 10% more B+ voltage than the
designers envisioned. So, your +225 will be +240V. You are running 50
more than spec, so your +225 will be +275, which will kill the caps and
shorten the lives of the tubes in your radio. (OBTW, the voltages I used
in the above description are just guesses. I am not certain what the
actual design voltage is for your radio.)


....

Next I removed the safety filter capacitors from the transformer primary
circuits. Fuse still blew. I traced out the primary circuit with a DVM
and found no short circuits in my wiring or from the transformer
windings to each other or to the transformer frame. With the transformer
completely taken out of the radio the fuse blowing stopped. I was
forced to conclude that the "new" transformer was a dud.

It was most likely damaged by the manufacturer. It is easy to nick a winding
through careless handling. The problem usually occurs where the inside end of
the primary (or secondary) crosses the windings to get to the outside where the
leads are attached. You can often cut the bobbin away, and find the short.


I don't have access right now to a variac, but I suspect that there
might be some sort of arcing in the transformer that doesn't show up
until higher voltages are applied. I still have this transformer, and I
might try looking at it again later this year when I can borrow a variac
from the university where I work.

Intermittent arcing is unlikely. Because of the relatively high currents,
and low voltages involved, it will usually burn off a wire, or weld it
permanently together.


I have replaced the suspect transformer and so far the radio is working
fine. My interest in using inrush current limiters is motivated by
trying to avoid a repeat of a damaged transformer, both in my father's
S-40B or my own.

Transformers are relatively immune to voltage spikes. For reasons of
manufacturing economy, the core is usually run right on the edge of where
it starts to become nonlinear (eg. saturation is beginning). If a spike
comes down the line, the spike will drive the core into saturation, and
that simple act will prevent the spike from being "transformed" to the
secondary. A lightning strike is a different matter. It will usually
cause an arc from the primary lead that is closest to the core to the core.
The lead will often be vaporized.


In spite of having a fancy microprocessor based Sony SW-77 to do my
SWLing on, I find using this old 'boatanchor' type radio irresistible.
After I finish up grad school (which I am starting rather late in life -
age 46) I plan to go for a ham license and possibly look into using
other BA gear.

They are a hoot! Welcome to the BA addiction/disease.

-Chuck

"Steven P. Burrows" wrote in message
news:lpbmg.57892$9c6.52561@dukeread11...
The B+ voltage delivered by the new transformer is about 50 volts higher
than Hallicrafters' original spec., which I was advised was not a big
problem. The other secondaries for the tube filaments and rectifier
filament were exactly right.


The "not a problem" transformer had a B+ of 25 V lower. Last year you
wrote:

"I have looked over the offerings from Antique Electronics Supply, and their
Fender transformers are a close match. Unfortunately, the Fender
transformers offered there top out at 325-0-325 V for the secondary
windings. I need a transformer with 350-0-350 V / 70 mA, 5 VAC / 2A, and
6.3 VAC / 2.6A secondary windings. "

http://groups.google.com/group/rec.r...ae22ac314cd44b




Throughout my use of this restored S-40B, I have been running it off of
a personal computer grade surge suppressor power strip, along with my
other old radios (others are solid state).

I replaced the power supply electrolytic caps with new ones, so I doubt
that this was a problem. From past experience with arcing in the
rectifier tube, I also looked into this possible cause. My rectifier
tube was also OK.

Be sure your power supply electrolytics can take the peak rectified B+. If
your new transformer is really putting out 375 V, the peak voltage is 525 V.

I'd be alot more comfortable if the B+ voltage was at the original spec or a
little below.



I pulled all of the tubes from the radio and powered it up in a darkened
room to attempt to see any potential arcing under the chassis. The fuse
blew, and there was no visible evidence of any problems in the radio
wiring.

Next I disconnected the secondaries of the power transformer from the
radio entirely. The fuse still blew.

Next I removed the safety filter capacitors from the transformer primary
circuits. Fuse still blew. I traced out the primary circuit with a DVM
and found no short circuits in my wiring or from the transformer
windings to each other or to the transformer frame. With the transformer
completely taken out of the radio the fuse blowing stopped. I was
forced to conclude that the "new" transformer was a dud.

Sure sounds like it.


I don't have access right now to a variac, but I suspect that there
might be some sort of arcing in the transformer that doesn't show up
until higher voltages are applied. I still have this transformer, and I
might try looking at it again later this year when I can borrow a variac
from the university where I work.

You can usually hear arcing. Smoke might also start coming out. It sounds
like you've got a dead short. There's a chance you might find it if you
take off the endbell and inspect the area carefully. Don't count on it.



I have replaced the suspect transformer and so far the radio is working
fine. My interest in using inrush current limiters is motivated by
trying to avoid a repeat of a damaged transformer, both in my father's
S-40B or my own.

In spite of having a fancy microprocessor based Sony SW-77 to do my
SWLing on, I find using this old 'boatanchor' type radio irresistible.
After I finish up grad school (which I am starting rather late in life -
age 46) I plan to go for a ham license and possibly look into using
other BA gear.

The S-40s are decent beginner radios in that they do work and they aren't
too hard to work on. But there are better radios out there!

Frank Dresser

The beauty of the old tube rigs is that they are pretty much immune to the
junk coming in the power line. In fact, they carried us through WWII with
poorly regulated power supplies, bullets and bombs. I believe the power
transformer burning out is due to either a defect in the transformer or
excessive load upon it. Leaky paper caps in the receiver can provide a
substantial load increase, and that may have been worsened by increased high
voltage.

Remember the radio is older than you are. How would you like it if you were
stressed to the breaking point? Well radio parts do not like it either -
expecially 50+ year old parts.

Once the S40 is "restored", it should keep running for the rest of your life
with almost no further maintenance. It need not be babied or just used on
special occasions. Many similar (but more expensive) radios were used in
communication facilities and left on 24 hours a day for 30 years before
retirement.

You can usually get S40 radios at swap meets for less than the cost of a
replacement transformer. I saw one at a swap meet last week that did not
sell for $50. The owner was just lowering the price when I went by so I
expect it could have been purchased for $25.

If you like the old radios, it is best to start buying as many as you can
get ahold of. Soon, you will need a separate building to store them. And,
46 is pretty young to start collecting. Most of the real collectors cannot
recall that long ago.

73, Colin K7FM

"Steven P. Burrows" wrote in message
news:461mg.57866$9c6.34117@dukeread11...
I recently completed restoring a pair of S-40B radios. The original
power transformers were pretty marginal, so I replaced them with similar
transformers that I bought from Antique Electronic Supply (the new
xfrmrs were Fender amp replacements). Everything seemed to work ok for
a couple of weeks of light use of my radio (I gave the other to my
father).

Last week while I was listening to my S-40B, its power supply blew a
fuse (a 5A cartridge fuse that I installed in the radio). I traced the
problem back to the "new" power transformer. It appeared to have a
short circuit of some kind, though I could never pin down exactly where
this short was using a DVM.

I've been using a 1A quick blow in my S-40A. Hasn't blown in six years of
semi-regular use. I used an analog AC current meter to estimate the fuse
value. My S-40A would always draw well under an amp except when I was hot
switching it. I had some 1A fuses handy so I tried one. I would have
raised the current rating if the fuse seemed touchy, but it seems to have
worked well.

The radio normally draws something like 60-70 watts. 1A at 120V is 120
watts. 5A at 120V is 600 watts.


The initial fuse blow occurred while the radio was running and my
house's central air conditioner was switching on. Up to that first fuse
blow, I noticed some significant flicker in the dial lamps (run off the
filament winding on the power transformer). At first I thought that I
was watching a dying lamp bulb, but now it seems that I was witnessing
the breakdown of the power transformer.

My question is, would installing an inrush current protector thermistor
in the primary winding circuit of this radio prevent a repeat of the
transformer breakdown? If this is a good move, what size of thermistor
should I use? Any help or recommendations would be appreciated.


Inrush current limiters are thermistors which have a higher cold resistance
than thier hot resistance. They limit current surges until they warm up and
then they have little effect. In your case, the radio would have been
operating and the current limiter would already have been hot. A inrush
current limiter would have made no difference.

Inrush current limiters really don't make much difference with equipment
which uses a rectifier tube, anyway. The tube gives an even gentler B+
startup than a inrush current limiter. The current limiter might help
protect tube heaters. I've experimented with inrush current limiters on
both transformer sets and series string sets. In both instances the dial
lamps would come up more gently. I don't think they make alot of practical
difference with transformer sets, but they might help protect the abused
heaters in a series string radio.


Steve Burrows


Frank Dresser

"Steven P. Burrows" wrote:

The B+ voltage delivered by the new transformer is about 50 volts higher
than Hallicrafters' original spec., which I was advised was not a big
problem. The other secondaries for the tube filaments and rectifier
filament were exactly right.

Throughout my use of this restored S-40B, I have been running it off of
a personal computer grade surge suppressor power strip, along with my
other old radios (others are solid state).

I replaced the power supply electrolytic caps with new ones, so I doubt
that this was a problem. From past experience with arcing in the
rectifier tube, I also looked into this possible cause. My rectifier
tube was also OK.

I pulled all of the tubes from the radio and powered it up in a darkened
room to attempt to see any potential arcing under the chassis. The fuse
blew, and there was no visible evidence of any problems in the radio wiring.

Next I disconnected the secondaries of the power transformer from the
radio entirely. The fuse still blew.

Next I removed the safety filter capacitors from the transformer primary
circuits. Fuse still blew. I traced out the primary circuit with a DVM
and found no short circuits in my wiring or from the transformer
windings to each other or to the transformer frame. With the transformer
completely taken out of the radio the fuse blowing stopped. I was
forced to conclude that the "new" transformer was a dud.

I don't have access right now to a variac, but I suspect that there
might be some sort of arcing in the transformer that doesn't show up
until higher voltages are applied. I still have this transformer, and I
might try looking at it again later this year when I can borrow a variac
from the university where I work.

I have replaced the suspect transformer and so far the radio is working
fine. My interest in using inrush current limiters is motivated by
trying to avoid a repeat of a damaged transformer, both in my father's
S-40B or my own.

In spite of having a fancy microprocessor based Sony SW-77 to do my
SWLing on, I find using this old 'boatanchor' type radio irresistible.
After I finish up grad school (which I am starting rather late in life -
age 46) I plan to go for a ham license and possibly look into using
other BA gear.


If the B+ is higher, the current load on the transformer goes up,
too. That higher current on the HV winding may have been more than the
transformer was built for.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I think the power tranny is ok. The problem is the line bypass caps. CHANGE
THEM.

--
Regards,
Gary...WZ1M
"Steven P. Burrows" wrote in message
news:461mg.57866$9c6.34117@dukeread11...
I recently completed restoring a pair of S-40B radios. The original
power transformers were pretty marginal, so I replaced them with similar
transformers that I bought from Antique Electronic Supply (the new
xfrmrs were Fender amp replacements). Everything seemed to work ok for
a couple of weeks of light use of my radio (I gave the other to my
father).

Last week while I was listening to my S-40B, its power supply blew a
fuse (a 5A cartridge fuse that I installed in the radio). I traced the
problem back to the "new" power transformer. It appeared to have a
short circuit of some kind, though I could never pin down exactly where
this short was using a DVM.

The initial fuse blow occurred while the radio was running and my
house's central air conditioner was switching on. Up to that first fuse
blow, I noticed some significant flicker in the dial lamps (run off the
filament winding on the power transformer). At first I thought that I
was watching a dying lamp bulb, but now it seems that I was witnessing
the breakdown of the power transformer.

My question is, would installing an inrush current protector thermistor
in the primary winding circuit of this radio prevent a repeat of the
transformer breakdown? If this is a good move, what size of thermistor
should I use? Any help or recommendations would be appreciated.

Steve Burrows