I am in the process of restoring a Hallicrafters S-40A
and have posted a bit about this already. First of all, I
replaced all the paper caps. This is generally recommended
when rebuilding old electronic equipment. Most of these were
the original wax filled types. I measured these for
capacitance and dissipation factor. D is the inverse of Q
and is a way of measuring ESR but has a constant value. The
result was:
One cap a dead short.
One cap open
The rest had C much higher than the marked value and rather
high D, anywhere from about 0.2 to about 0.5, I think one
was even higher. There were a couple of molded plastic caps,
one a blue colored Cornell-Dubilier the other an Astron.
These were probably replacements. Both were close to the
marked C value with D of around 0.1, probably still good.
The paper caps were made by Industrial Condenser Co, of
Chicago and Sprague.
For comparison, new film caps measure right on the nose
for C and have D too low to measure on this bridge.
The measurements were made on a General Radio Type
650A, an oldie but goodie, which has been calibrated with
precision resistors and caps. The capacitance measurements
are made at 1.0Khz. If I get curious enough I may check the
RF impedance of a couple of these caps on a Q meter but I
suspect they are not very good.
While the high C value may not seem to be a problem I
suspect it may indicate some deformation of the capacitor
elements or some other problem. These were not remotely
precision caps when made but the values are so far off the
marked values that I suspect a change in the internals
rather than manufacturing tollerance.
So, the advice to shotgun paper caps seems to be right
on.

Another note, probably should be a separate post.
I mentioned before that the bandspread cap went the
opposite direction of any other I've seen in a Hallicrafters
RX. I got a couple of responses that others also had similar
S-40's. I found a couple of other oddities in my receiver
(for instance someone had connected the output of the BFO
directly to the detecto rather than by means of the wire
"gimmic" cap, it won't work this way). I am now pretty much
convinced that the band spread cap was modified to make it
"set" at 100 rather than the usual zero used in H receivers.
I was able to make it go in the right direction by crossing
the dial drive cable but I don't like makeshifts. Also,
despite the nearly symmetrical construction of the band
spread cap I suspect the minimum capacitance is slightly
different when its running in the correct direction. That
would affect the "normal" dial calibration. The RX
calibrates OK but I am still going to have a go at removing
the stop peg. I think I will have to drill it out but will
try something less "invasive" first.
BTW, I used to consider Hallicrafters stuff junk but
after rebuilding this set and an S-20R have changed my
mind. Actually both are well made and well designed.
Hallicrafters definitely built their equipment to fit
certain price ranges, mostly economy. I think they did quite
well in delivering good performance value at the prices they
aimed at. One proof is that the stuff is still working after
60 or 70 or more years.
The above really applies to the components too. While
paper caps have a bad reputation keep in mind that most of
the ones we deal with are very old and have worked well for
a long time. Plastic film was not available when these guys
were made and other types of caps, mostly tin-can oil-filled
types, were very expensive in comparison to the common wax
filled types. I am not sure they lasted any longer. One
exception is the oil-filled molded plastic Sprague Black
Beauty cap. These were made and sold as extra-high quality,
long life caps but Sangamo evidenty had manufacturing
problems, one of which was the way the oil filling tube was
sealed. These began failing within a couple of years of
manufacture where the "less reliable" wax filled paper caps
went along for many decades.


--

--
Richard Knoppow
Los Angeles
WB6KBL

While the high C value may not seem to be a problem I suspect it may
indicate some deformation of the capacitor elements or some other problem.

I suspect the the high C reading is not due to a real capacity increase, but
rather to the fact that the meter shows a C higher than real when the measured
capacitor is very lossy, i.e. it has a fairly low resistance in parallel.

73

Tony I0JX

"Richard Knoppow" wrote in message
I am in the process of restoring a Hallicrafters S-40A and have
posted a bit about this already. First of all, I replaced all the paper
caps. This is generally recommended when rebuilding old electronic
equipment. Most of these were the original wax filled types. I measured
these for capacitance and dissipation factor. D is the inverse of Q and is
a way of measuring ESR but has a constant value. The result was:
One cap a dead short.
One cap open
The rest had C much higher than the marked value and rather high D,
anywhere from about 0.2 to about 0.5, I think one was even higher. There
were a couple of molded plastic caps, one a blue colored Cornell-Dubilier
the other an Astron. These were probably replacements. Both were close to
the marked C value with D of around 0.1, probably still good. The paper
caps were made by Industrial Condenser Co, of Chicago and Sprague.
For comparison, new film caps measure right on the nose for C and have
D too low to measure on this bridge.
The measurements were made on a General Radio Type 650A, an oldie but
goodie, which has been calibrated with precision resistors and caps. The
capacitance measurements are made at 1.0Khz. If I get curious enough I may
check the RF impedance of a couple of these caps on a Q meter but I
suspect they are not very good.
While the high C value may not seem to be a problem I suspect it may
indicate some deformation of the capacitor elements or some other problem.
These were not remotely precision caps when made but the values are so far
off the marked values that I suspect a change in the internals rather than
manufacturing tollerance.
So, the advice to shotgun paper caps seems to be right on.

Another note, probably should be a separate post.
I mentioned before that the bandspread cap went the opposite direction
of any other I've seen in a Hallicrafters RX. I got a couple of responses
that others also had similar S-40's. I found a couple of other oddities in
my receiver (for instance someone had connected the output of the BFO
directly to the detecto rather than by means of the wire "gimmic" cap, it
won't work this way). I am now pretty much convinced that the band spread
cap was modified to make it "set" at 100 rather than the usual zero used
in H receivers. I was able to make it go in the right direction by
crossing the dial drive cable but I don't like makeshifts. Also, despite
the nearly symmetrical construction of the band spread cap I suspect the
minimum capacitance is slightly different when its running in the correct
direction. That would affect the "normal" dial calibration. The RX
calibrates OK but I am still going to have a go at removing the stop peg.
I think I will have to drill it out but will try something less "invasive"
first.
BTW, I used to consider Hallicrafters stuff junk but after rebuilding
this set and an S-20R have changed my mind. Actually both are well made
and well designed. Hallicrafters definitely built their equipment to fit
certain price ranges, mostly economy. I think they did quite well in
delivering good performance value at the prices they aimed at. One proof
is that the stuff is still working after 60 or 70 or more years.
The above really applies to the components too. While paper caps have
a bad reputation keep in mind that most of the ones we deal with are very
old and have worked well for a long time. Plastic film was not available
when these guys were made and other types of caps, mostly tin-can
oil-filled types, were very expensive in comparison to the common wax
filled types. I am not sure they lasted any longer. One exception is the
oil-filled molded plastic Sprague Black Beauty cap. These were made and
sold as extra-high quality, long life caps but Sangamo evidenty had
manufacturing problems, one of which was the way the oil filling tube was
sealed. These began failing within a couple of years of manufacture where
the "less reliable" wax filled paper caps went along for many decades.

Anyone ever bother to check resistor values? During overhaul and repair
of lots of tube era marine electronics, many composition (and films
sometimes) resistors had changed value considerably. Especially those used
in voltage dropping circuits. High value resistors ( half megohm or more)
seemed to be pretty wild too.
Of course checking frequently meant disconnecting from associated
circuitry to check is a real
pain in the you know what, but the end result, (including the condenser
replacements) resulted in amazing results!
Anybody find similar resistor drift?

Old Chief Lynn

"Lynn" wrote in message
...

"Richard Knoppow" wrote in
message
I am in the process of restoring a Hallicrafters
S-40A and have posted a bit about this already. First of
all, I replaced all the paper caps. This is generally
recommended when rebuilding old electronic equipment.
Most of these were the original wax filled types. I
measured these for capacitance and dissipation factor. D
is the inverse of Q and is a way of measuring ESR but has
a constant value. The result was:
One cap a dead short.
One cap open
The rest had C much higher than the marked value and
rather high D, anywhere from about 0.2 to about 0.5, I
think one was even higher. There were a couple of molded
plastic caps, one a blue colored Cornell-Dubilier the
other an Astron. These were probably replacements. Both
were close to the marked C value with D of around 0.1,
probably still good. The paper caps were made by
Industrial Condenser Co, of Chicago and Sprague.
For comparison, new film caps measure right on the
nose for C and have D too low to measure on this bridge.
The measurements were made on a General Radio Type
650A, an oldie but goodie, which has been calibrated with
precision resistors and caps. The capacitance
measurements are made at 1.0Khz. If I get curious enough
I may check the RF impedance of a couple of these caps on
a Q meter but I suspect they are not very good.
While the high C value may not seem to be a problem I
suspect it may indicate some deformation of the capacitor
elements or some other problem. These were not remotely
precision caps when made but the values are so far off
the marked values that I suspect a change in the
internals rather than manufacturing tollerance.
So, the advice to shotgun paper caps seems to be
right on.

Another note, probably should be a separate post.
I mentioned before that the bandspread cap went the
opposite direction of any other I've seen in a
Hallicrafters RX. I got a couple of responses that others
also had similar S-40's. I found a couple of other
oddities in my receiver (for instance someone had
connected the output of the BFO directly to the detecto
rather than by means of the wire "gimmic" cap, it won't
work this way). I am now pretty much convinced that the
band spread cap was modified to make it "set" at 100
rather than the usual zero used in H receivers. I was
able to make it go in the right direction by crossing the
dial drive cable but I don't like makeshifts. Also,
despite the nearly symmetrical construction of the band
spread cap I suspect the minimum capacitance is slightly
different when its running in the correct direction. That
would affect the "normal" dial calibration. The RX
calibrates OK but I am still going to have a go at
removing the stop peg. I think I will have to drill it
out but will try something less "invasive" first.
BTW, I used to consider Hallicrafters stuff junk but
after rebuilding this set and an S-20R have changed my
mind. Actually both are well made and well designed.
Hallicrafters definitely built their equipment to fit
certain price ranges, mostly economy. I think they did
quite well in delivering good performance value at the
prices they aimed at. One proof is that the stuff is
still working after 60 or 70 or more years.
The above really applies to the components too. While
paper caps have a bad reputation keep in mind that most
of the ones we deal with are very old and have worked
well for a long time. Plastic film was not available when
these guys were made and other types of caps, mostly
tin-can oil-filled types, were very expensive in
comparison to the common wax filled types. I am not sure
they lasted any longer. One exception is the oil-filled
molded plastic Sprague Black Beauty cap. These were made
and sold as extra-high quality, long life caps but
Sangamo evidenty had manufacturing problems, one of which
was the way the oil filling tube was sealed. These began
failing within a couple of years of manufacture where the
"less reliable" wax filled paper caps went along for many
decades.

Anyone ever bother to check resistor values? During
overhaul and repair of lots of tube era marine
electronics, many composition (and films sometimes)
resistors had changed value considerably. Especially those
used in voltage dropping circuits. High value resistors
( half megohm or more) seemed to be pretty wild too.
Of course checking frequently meant disconnecting from
associated circuitry to check is a real
pain in the you know what, but the end result, (including
the condenser replacements) resulted in amazing results!
Anybody find similar resistor drift?

Old Chief Lynn
I do check resistor values. Its typical for carbon
composition resistors (aka mud resistors) to go up in value
when heated and with age. For the most part these were not
precision resistors although some were sold as 5% resistors.
Most of those found in equipment built before about 1946
were +/- 20%. After that 10% tollerance was more usual. They
can be quite far off but seldom fail catastrophically. Also,
composition resistors are noisy and were always noisy even
when new. IMO Ohmite were the best of a bad lot.
Older carbon film resistors often had staked end caps.
The caps can develop poor contact or even corrosion at which
point the resistor goes open. Many early metal film
resistors used a similar method of attaching leads. If done
right end capped units can be quite reliable but many were
not. Another method of attaching leads was used primarily on
precision resistors and high reliability parts. This was the
use of conductive epoxy resin to glue the ends of the leads
to holes in the ceramic core. When made correctly the break
stength of the connection is greater than the wire lead.
Metal film resistors can be made to have a very low or even
zero temperature co-efficient and, in general, are the
quietest of resistors. Both deposited carbon and metal
resistors can go open if sufficiently overloaded. Military
parts are tested for a seven times overload in manufacture.
The bad ones sound like Chinese fireworks going off.


--

--
Richard Knoppow
Los Angeles
WB6KBL

"Antonio Vernucci" wrote in message
.. .
While the high C value may not seem to be a problem I
suspect it may indicate some deformation of the capacitor
elements or some other problem.

I suspect the the high C reading is not due to a real
capacity increase, but rather to the fact that the meter
shows a C higher than real when the measured capacitor is
very lossy, i.e. it has a fairly low resistance in
parallel.

73

Tony I0JX
That might happen using a capacitance meter than does
not measure the series and parallel resistance. The GR
bridge does, which is not to say that you might not be
right. It will measure capacitors that my Tektronix
multi-meter will not measure, or, rather, will not give a
stable indication on. Whatever is the case, these are bad
guys indeed.
My main reason for mentioning this was to confirm the
wisdom replacing paper caps where they are encountered.


--

--
Richard Knoppow
Los Angeles
WB6KBL

On Mar 13, 12:33*am, "Lynn" wrote:
* * *Anyone ever bother to check resistor values? During overhaul and repair
of lots of tube era marine electronics, many composition (and films
sometimes) resistors had changed value considerably. Especially those used
in voltage dropping circuits. High value resistors ( half megohm or more)
seemed to be pretty wild too.
* * *Of course checking frequently meant disconnecting from associated
circuitry to check is a real
pain in the you know what, but the end result, (including the condenser
replacements) resulted in amazing results!
* * *Anybody find similar resistor drift?

I do. My general rule is to replace or bridge resistors if they
deviate 15 percent or more from their marked value. However, if their
value isn't all that critical (e.g. a large value resistor in series
with a screen grid), I'll leave it alone. I prefer to replace rather
than bridge; however, if I don't have a suitable replacement I'll
bridge if the resistor has drifted up in value, which is often the
case.

Dave Drumheller, K3WQ

I have found, over the years, that carbon comp resistors go high. In some
restorations, especially on radios that you just want to function, I leave
the resistors alone, where they have increased in value moderately. My
reasoning is that since the line voltage is higher now, a reduction in
voltage caused by the higher value resistors, will somewhat compensate for
the increased voltage. This would especially apply to screen and cathode
resistors.

However, in critical work, it may pay to pay attention to the resistors. My
Collins receiver uses a bridge circuit for the S-meter and the zero point
kept changing. At first I thought it was a leaky capacitor. I checked,
then finally replaced them. No improvement. I then carefully checked the
tubes. No improvement. Finally, I replaced the carbon comp resistors with
stable ones and the meter drift was cured.

73, Colin K7FM

Lynn wrote:

Anyone ever bother to check resistor values? During overhaul and repair
of lots of tube era marine electronics, many composition (and films
sometimes) resistors had changed value considerably. Especially those used
in voltage dropping circuits. High value resistors ( half megohm or more)
seemed to be pretty wild too.
Of course checking frequently meant disconnecting from associated
circuitry to check is a real
pain in the you know what, but the end result, (including the condenser
replacements) resulted in amazing results!
Anybody find similar resistor drift?

My general method is to check them all in-circuit with a DVM. The thing is,
resistors tend to fail by rising in value, rather than falling. And the errors
due to in-circuit testing all reduce the measured value (since there is stuff
shunted around them).

So, if the measured value is lower than it should be, I go on to the next
resistor. But if the measured value is more than 10% or so higher than the
value on the resistor, I'll replace it.

Sometimes I miss resistors this way, since if a much lower value thing
is across it, the test is useless. But it doesn't take more than a few
minutes it and catches a lot of them.

Things like plate resistors often are worries, because they are generally
pretty high values, they tend to get hot, and they are in a part of the
circuit where if they get noisy it'll be a problem.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

That might happen using a capacitance meter than does
not measure the series and parallel resistance. The GR
bridge does, which is not to say that you might not be
right.

Dick,

what I meant to say isd the following.

That might happen using a capacitance meter than does
not measure the series and parallel resistance. The GR
bridge does, which is not to say that you might not be
right.

Dick,

what I meant to say is the following:

At 1kHz, a 500 pF capacitor with a 500,000 ohm resistance in parallel is
equivalent to the series of of 702 pF capacitor and 144,200 ohm resistior
(using the well known parallel-to-seriel translation formulas).

So, if your meter has the ability to separately measure the series resistance
and capacitance, it should correctly indicate 702 pF, i.e. a value higher than
that marked on the capacitor.

73

Tony I0JX