hallicrafters s-40a, bad band(s)
 

this is the first more complex (than s38s) halli have i tried to
repair. as received, the set. set played, but w/out sensitivity or
vol. recapped (not micas) and tested all tubes, replacing as needed.
checked resistors, and replaced a few. set also had severe crackling
which matched 'short in a tuning cap' as described in marcus and levy.
i replaced the tuning condensor, due to remaining crackles i simply
couldn't get out w/cleaning. crackles went away w/partswap and set
appeared to align well -- used scope across output to voice coil. got
good volume and nice waves as i went thru the IF and the band steps.
for IF the sig gen was connected to the center of the gang, the middle
of 3 posts on the top of it, w/the ground to the chassis and the gang
fully open.

radio plays well on band 3 -- good vol on strong station, many stations
w/short wire. picks up similarly on band 2 down to about 4 mhz.

bc is silent except for what sounds like a couple of spots that 'want
to be' stations. very faint voice heard in one spot. band 4 seems to
be similar.

a quick reattach of sig gen, and good tones heard all bands at align
freq for those bands, and good IF tone. bandswitch was checked and
cleaned. seems to be making good contact w/clean click/pop as changed
w/set on. a little puzzled where to look because of this.

docs say make sure the image freq is out of the way of oscillator freq
for bands. i don't quite understand what this means, or how to be sure
they aren't colliding, but i think i may have misaligned the base IF?
maybe aligned with an image of it? have noticed when aligning other
sets, you can find several positions that ring w/the tone, but only one
that rings best. is this the result of getting the echo instead of the
original? care was taken on the rf aligns to find thru most of the adj
range for the best response. but did not try moving the if's
radically.
ab

hallicrafters s-40a, bad band(s)
 

"ablebravo" wrote in message
ups.com...
this is the first more complex (than s38s) halli have i tried to
repair. as received, the set. set played, but w/out sensitivity or
vol. recapped (not micas) and tested all tubes, replacing as needed.
checked resistors, and replaced a few. set also had severe crackling
which matched 'short in a tuning cap' as described in marcus and levy.
i replaced the tuning condensor, due to remaining crackles i simply
couldn't get out w/cleaning. crackles went away w/partswap and set
appeared to align well -- used scope across output to voice coil. got
good volume and nice waves as i went thru the IF and the band steps.
for IF the sig gen was connected to the center of the gang, the middle
of 3 posts on the top of it, w/the ground to the chassis and the gang
fully open.

radio plays well on band 3 -- good vol on strong station, many stations
w/short wire. picks up similarly on band 2 down to about 4 mhz.

bc is silent except for what sounds like a couple of spots that 'want
to be' stations. very faint voice heard in one spot. band 4 seems to
be similar.

a quick reattach of sig gen, and good tones heard all bands at align
freq for those bands, and good IF tone. bandswitch was checked and
cleaned. seems to be making good contact w/clean click/pop as changed
w/set on. a little puzzled where to look because of this.

docs say make sure the image freq is out of the way of oscillator freq
for bands. i don't quite understand what this means, or how to be sure
they aren't colliding, but i think i may have misaligned the base IF?
maybe aligned with an image of it? have noticed when aligning other
sets, you can find several positions that ring w/the tone, but only one
that rings best. is this the result of getting the echo instead of the
original? care was taken on the rf aligns to find thru most of the adj
range for the best response. but did not try moving the if's
radically.
ab


First, carefully clean the band switch wafer metal wipers with a cotton
Q-tip and some DeOxit.
No need for heavy handiness here -- just good patient (methodical) cleaning.
IF you are short on time or not patient that day -- do something else and
come back to it.

gb

hallicrafters s-40a, bad band(s)
 

have done, 3 times, just as you say. the fingers seems to make good
contact (rise and fall as the switch is cycled). i can certainly do
again. i guess what i don't get is how i can get a nice signal thru
w/the gen -- tune the test signal and its images, but not tune
stations. i don't have a whole lot of experience w/this.
ab

First, carefully clean the band switch wafer metal wipers with a cotton
Q-tip and some DeOxit.
No need for heavy handiness here -- just good patient (methodical) cleaning.
IF you are short on time or not patient that day -- do something else and
come back to it.

gb

hallicrafters s-40a, bad band(s)
 

ablebravo wrote:
have done, 3 times, just as you say. the fingers seems to make good
contact (rise and fall as the switch is cycled). i can certainly do
again. i guess what i don't get is how i can get a nice signal thru
w/the gen -- tune the test signal and its images, but not tune
stations. i don't have a whole lot of experience w/this.
ab

First, carefully clean the band switch wafer metal wipers with a cotton
Q-tip and some DeOxit.
No need for heavy handiness here -- just good patient (methodical) cleaning.
IF you are short on time or not patient that day -- do something else and
come back to it.

gb


Perhaps you are simply trying to receive stations on bands for which
there is poor propagation during that particular time of day....

jak

hallicrafters s-40a, bad band(s)
 

I believe your antenna coil is open...Look at schematic and find
BC band coil,check continuity from ant post to ground... coil is
probably open..This sometimes happens when lightning sends a surge via
an external antenna,burns out the ant coil on the band that is selected
at the time..You may be able to repair the coil if that is the
problem...GL HS
jakdedert wrote:
ablebravo wrote:
have done, 3 times, just as you say. the fingers seems to make good
contact (rise and fall as the switch is cycled). i can certainly do
again. i guess what i don't get is how i can get a nice signal thru
w/the gen -- tune the test signal and its images, but not tune
stations. i don't have a whole lot of experience w/this.
ab

First, carefully clean the band switch wafer metal wipers with a cotton
Q-tip and some DeOxit.
No need for heavy handiness here -- just good patient (methodical) cleaning.
IF you are short on time or not patient that day -- do something else and
come back to it.

gb


Perhaps you are simply trying to receive stations on bands for which
there is poor propagation during that particular time of day....

jak

hallicrafters s-40a, bad band(s)
 

I believe your antenna coil is open...Look at schematic and find
BC band coil,check continuity from ant post to ground... coil is
probably open..This sometimes happens when lightning sends a surge via
an external antenna,burns out the ant coil on the band that is selected
at the time..You may be able to repair the coil if that is the
problem...GL HS
jakdedert wrote:
ablebravo wrote:
have done, 3 times, just as you say. the fingers seems to make good
contact (rise and fall as the switch is cycled). i can certainly do
again. i guess what i don't get is how i can get a nice signal thru
w/the gen -- tune the test signal and its images, but not tune
stations. i don't have a whole lot of experience w/this.
ab

First, carefully clean the band switch wafer metal wipers with a cotton
Q-tip and some DeOxit.
No need for heavy handiness here -- just good patient (methodical) cleaning.
IF you are short on time or not patient that day -- do something else and
come back to it.

gb


Perhaps you are simply trying to receive stations on bands for which
there is poor propagation during that particular time of day....

jak

hallicrafters s-40a, bad band(s)
 

I believe your antenna coil is open...Look at schematic and find
BC band coil,check continuity from ant post to ground... coil is
probably open..This sometimes happens when lightning sends a surge via
an external antenna,burns out the ant coil on the band that is selected
at the time..You may be able to repair the coil if that is the
problem...GL HS
jakdedert wrote:
ablebravo wrote:
have done, 3 times, just as you say. the fingers seems to make good
contact (rise and fall as the switch is cycled). i can certainly do
again. i guess what i don't get is how i can get a nice signal thru
w/the gen -- tune the test signal and its images, but not tune
stations. i don't have a whole lot of experience w/this.
ab

First, carefully clean the band switch wafer metal wipers with a cotton
Q-tip and some DeOxit.
No need for heavy handiness here -- just good patient (methodical) cleaning.
IF you are short on time or not patient that day -- do something else and
come back to it.

gb


Perhaps you are simply trying to receive stations on bands for which
there is poor propagation during that particular time of day....

jak

hallicrafters s-40a, bad band(s)
 

checked against a zenith transoceanic, same bands same time of day. i
guess a better phrasing would be, 'could misalignment (image maybe)
cause these problems. i will check the coil, but suspect ok. before
pulling the old tuner cap, could receive bc outside the areas it was
crackling on.
ab
jakdedert wrote:
ablebravo wrote:
have done, 3 times, just as you say. the fingers seems to make good
contact (rise and fall as the switch is cycled). i can certainly do
again. i guess what i don't get is how i can get a nice signal thru
w/the gen -- tune the test signal and its images, but not tune
stations. i don't have a whole lot of experience w/this.
ab

First, carefully clean the band switch wafer metal wipers with a cotton
Q-tip and some DeOxit.
No need for heavy handiness here -- just good patient (methodical) cleaning.
IF you are short on time or not patient that day -- do something else and
come back to it.

gb


Perhaps you are simply trying to receive stations on bands for which
there is poor propagation during that particular time of day....

jak

Hallicrafters S-40A, bad band(s)
 

"ablebravo" wrote in message
oups.com...
have done, 3 times, just as you say. the fingers seems to make good
contact (rise and fall as the switch is cycled). i can certainly do
again. i guess what i don't get is how i can get a nice signal thru
w/the gen -- tune the test signal and its images, but not tune
stations. i don't have a whole lot of experience w/this.
ab

Well if you removed visible tarnish (brown or black) you are then
likely okay in that department.

You have performed the alignment, right?

gb

hallicrafters s-40a, bad band(s)
 

"ablebravo" wrote in message
ups.com...
this is the first more complex (than s38s) halli have i tried to
repair. as received, the set. set played, but w/out sensitivity or
volume ... [snip].
docs say make sure the image freq is out of the way of oscillator freq
for bands. i don't quite understand what this means, or how to be sure
they aren't colliding, but i think i may have misaligned the base IF?
maybe aligned with an image of it? have noticed when aligning other
sets, you can find several positions that ring w/the tone, but only one
that rings best. is this the result of getting the echo instead of the
original? care was taken on the rf aligns to find thru most of the adj
range for the best response. but did not try moving the if's
radically.
ab


Yes, after I reread your first post -- you may have aligned this incorrectly
Bruce McCalley has a good article on this subject for restorers
http://www.antiqueradios.org/gazette/align.htm

OR it may be ....
http://www.burnyourbonus.net/rec.rad...thread306.html

http://bama.sbc.edu/hallicra.htm

I would suggest looking at these S-40A web pages (and owners who have also
performed major restorations and alignments on this model)

Phillip I. Nelson (a good documentation restorer)
http://antiqueradio.org/halli02.htm

VE7SL
http://imagenisp.ca/jsm/s40.html
"A close inspection of the BFO circuit indicated a previous but unsuccessful
repair attempt. As the Hallicrafter's engineers often liked to do in BFO
circuits, a gimmick capacitor consisting of two short twisted wires was used
to couple the BFO signal into the detector. This particular S-40 had one of
the two wires soldered to the correct tube pin but the other one (to twist
together with) was not to be found. Examining the tube pin showed no
indication that there ever had been a second wire as the solder was smooth,
original and undisturbed. The one wire that was installed showed no
indication of ever being twisted with another. It is likely that the BFO
circuit on radio 12,733 never did work, right off the Rogers Majestic
assembly line in Toronto.
Perhaps it was wired or tested very late on a Friday afternoon, back in
1947! "

http://portabletubes.co.uk/boats/hs40.htm

hallicrafters s-40a, bad band(s)
 

"ablebravo" wrote in message
ups.com...
this is the first more complex (than s38s) halli have i
tried to
repair. as received, the set. set played, but w/out
sensitivity or
vol. recapped (not micas) and tested all tubes, replacing
as needed.
checked resistors, and replaced a few. set also had
severe crackling
which matched 'short in a tuning cap' as described in
marcus and levy.
i replaced the tuning condensor, due to remaining crackles
i simply
couldn't get out w/cleaning. crackles went away
w/partswap and set
appeared to align well -- used scope across output to
voice coil. got
good volume and nice waves as i went thru the IF and the
band steps.
for IF the sig gen was connected to the center of the
gang, the middle
of 3 posts on the top of it, w/the ground to the chassis
and the gang
fully open.

radio plays well on band 3 -- good vol on strong station,
many stations
w/short wire. picks up similarly on band 2 down to about
4 mhz.

bc is silent except for what sounds like a couple of spots
that 'want
to be' stations. very faint voice heard in one spot.
band 4 seems to
be similar.

a quick reattach of sig gen, and good tones heard all
bands at align
freq for those bands, and good IF tone. bandswitch was
checked and
cleaned. seems to be making good contact w/clean
click/pop as changed
w/set on. a little puzzled where to look because of this.

docs say make sure the image freq is out of the way of
oscillator freq
for bands. i don't quite understand what this means, or
how to be sure
they aren't colliding, but i think i may have misaligned
the base IF?
maybe aligned with an image of it? have noticed when
aligning other
sets, you can find several positions that ring w/the tone,
but only one
that rings best. is this the result of getting the echo
instead of the
original? care was taken on the rf aligns to find thru
most of the adj
range for the best response. but did not try moving the
if's
radically.
ab

This last means to make sure the local oscillator is on
the correct side of the signal, that is, make sure you are
not peaking up the image of the desired signal. This is most
likely on the top band (band 4) since image suppression will
probably be adequate to prevent it on the lower bands. The
oscillator of the S-40 and S-40-A is above the signal
frequency on bands 1,2,and 3, and below it on band 4. If you
have the oscillator on the wrong side of the signal the
sensitivity will be low and the frequency calibration off.
You can measure the oscillator frequency with another radio
with similar frequency range, just pick up its radiation on
the the receiver. You don't need anyhing too accurate, just
enough to tell within 455khz of where the oscillator is.
This problem is very unlikely on the BC band but might well
be the problem on band 4. Another receiver will also tell
you if the oscillator is weak or cutting out at some points
on the band.
Since you know the IF stages work OK the problem is
isolated to the RF or Mixer stages. You can probably check
the mixer by injecting a signal directly into it. Probably a
wire wound around the tube (with shield off) a few times
will get enough signal into it. It won't be as sensitive as
normal but should give you some response. If this seems to
work OK the problem is in the RF amp.
Someone suggested one or more antenna primary coils may
be open. This is possible and does not have to be damage
from lightning. Its easy to check, just put an ohm meter
across the two antenna terminals on the back of the set
(with the ground link open) and measure the resistance. It
will vary with the band but should be pretty low for all. If
the coil is open you will get an open circuit indication on
the ohm meter. Sometimes all that happens is that the solder
connections at the ends of the coil have opened up. Often
just heating them with a little extra solder will fix the
coil. Lightning damage is usually pretty extreme and easy to
spot.
It sounds like you have a service manual. You might check
the manuals available on the BAMA site, there are several
covering the S-40 and S-40A. While there are differences the
two are enough alike so that the rather complete technical
manual for the S-40 may be of some help. I would download
everything there that pertains to this receiver, there may
be a hint in one that is missed in the others.
BTW, I am surprized that it was necessary to replace the
tuning capacitor. Variable capacitors are usually noisy due
to dirt between the plates or intermittant ground
connections to the rotor. Lubricating the bearings with a
tuner lubricant may also help. Make sure the replacement
capacitor isn't going open at some points.
See if any of this helps. You can also contact me via
e-mail if you want. The first time you will get a spam
blocker message. I will also follow this thread in this
group and respond here if you prefer.
Good luck in restoring this thing, its a neat little
receiver.


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

hallicrafters s-40a, bad band(s)
 

yep using bama copy halli s40a service guide. have sams. reread phil
for first 4 sets i did. will read bruce w/interest, but some over my
head. think i will retry if align since cleaned band again w/no
change. band rotors look pretty good. have located the band 1 related
coils and will try to figure out how to test for opens....4
solderpoints per coil.... not sure which should be connected to meter.

thank you all for your patience and advice
ab

hallicrafters s-40a, bad band(s)
 

"ablebravo" wrote in message
ups.com...
yep using bama copy halli s40a service guide. have sams. reread phil
for first 4 sets i did. will read bruce w/interest, but some over my
head. think i will retry if align since cleaned band again w/no
change. band rotors look pretty good. have located the band 1 related
coils and will try to figure out how to test for opens....4
solderpoints per coil.... not sure which should be connected to meter.

thank you all for your patience and advice
ab

Richard reminded me of one other point .. check you coils in the BC (band
1).

Phil found bad capacitors in some of these sections or inside cans (great
way to ruin the day) ...
finding and replacing resolved his sensitivity and peaking.
Note that many have commented that sensitivity was lousy (compared to what?)
on band 1.

gb

hallicrafters s-40a, bad band(s)
 

thx richard. esp on how to test the coils. i will do that before
checking the IF again. i am suspecting the IF because a couple of the
adjustments were near the travel limit, which may mean i am in wrong
place. where it works, it's hot.

i was pretty sure on the tuning gang -- could adjust the vanes and get
the crackle to change and nearly disappear. i flushed it good, blew it
out and cleaned and cleaned. after spending hours on it, i bought the
part. i think something might have been in the bearings. in the
'crackle spot' the signal died and set could not be aligned. it
blotted out some of the align freqs. no such prob w/replacement part.

ab

hallicrafters s-40a, bad band(s)
 

"ablebravo" wrote in message
ups.com...
thx richard. esp on how to test the coils. i will do
that before
checking the IF again. i am suspecting the IF because a
couple of the
adjustments were near the travel limit, which may mean i
am in wrong
place. where it works, it's hot.

i was pretty sure on the tuning gang -- could adjust the
vanes and get
the crackle to change and nearly disappear. i flushed it
good, blew it
out and cleaned and cleaned. after spending hours on it,
i bought the
part. i think something might have been in the bearings.
in the
'crackle spot' the signal died and set could not be
aligned. it
blotted out some of the align freqs. no such prob
w/replacement part.

ab

Do you have a signal generator of some sort? I thought
from your posts that you do. You really do need one to set
up the IF amplifiers. It should be capable of putting out
455 khz preferably with some modulation. The usual
requirement is for 400hz at about 30%. The modulation level
is not critical but most signal generators are not capable
of high modulation level.
Its also helpful to have a crystal calibrator, preferably
one which puts out fairly low frequency markers in addition
to higher frequency ones. 10khz is nice to have. Mine has
100khz, 1.0 mhz, and 10mhz. This can be used directly to
calibrate the receiver and also to calibrate the signal
generator. If you don't have these tools perhaps you can
borrow them.
If the IF transformers are near the limit of their
adjustment, and you know the test frequency is correct, its
probable the resonating capacitors have drifted in value. I
believe this receiver uses permeablility tuned IF coils
(asjustable dust cores).
Again, since the problem seems to be isolated to two
bands and at least one band works OK I think the IF is not
at fault, or at least not the main cause of trouble. I
suggest checking the wiring of the tuning capacitor again to
make sure its OK. You might want to check the other
capacitors in the oscillator and RF stage. I am suspicious
of the oscillator because you say it quits near the low end
of one band. That sound to me like a bad coupling capacitor
there. If you have access to a good RF voltmeter or
reasonably wide band oscilloscope you can check the output
of the oscillator. Even a pick-up loop will show if the
output is varying a lot or if the LO is quitting at the low
end of a band.
Just some things to look for. Remember, this RX is more
than fifty years old so it may have a lot of tired parts (so
do I).


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

hallicrafters s-40a, bad band(s)
 

thanks again, richard. i am printing this whole train out to go down
everyone's checklists. yes, i have an eico sig gen,almost as old as
the set. i check it against an aor 8200 scanner set for the target
freq at each alignment. it is usually really close to right on the
money. have an old tek 465b 200mhz, which is still something of a
mystery, but i can use it in simple ways. i think i can find the
output. tube-tested the mixer/osci tube itself, and again got ok.

have also an eico signal tracer, but have only read a bit about how to
use.

i do plan to check the tuning cap wiring. i did redo the solder
joints, and while i did photo and mark the wires as the old came out, i
could have made a mistake. it should be easy to undo and jumper to
check -- mistake would have to be in center gang area. wires not long
enough to grossly change where they go.
it will take me a while to go thru all this -- thank you all.
ab

Richard Knoppow wrote:
"ablebravo" wrote in message
ups.com...
thx richard. esp on how to test the coils. i will do
that before
checking the IF again. i am suspecting the IF because a
couple of the
adjustments were near the travel limit, which may mean i
am in wrong
place. where it works, it's hot.

i was pretty sure on the tuning gang -- could adjust the
vanes and get
the crackle to change and nearly disappear. i flushed it
good, blew it
out and cleaned and cleaned. after spending hours on it,
i bought the
part. i think something might have been in the bearings.
in the
'crackle spot' the signal died and set could not be
aligned. it
blotted out some of the align freqs. no such prob
w/replacement part.

ab

Do you have a signal generator of some sort? I thought
from your posts that you do. You really do need one to set
up the IF amplifiers. It should be capable of putting out
455 khz preferably with some modulation. The usual
requirement is for 400hz at about 30%. The modulation level
is not critical but most signal generators are not capable
of high modulation level.
Its also helpful to have a crystal calibrator, preferably
one which puts out fairly low frequency markers in addition
to higher frequency ones. 10khz is nice to have. Mine has
100khz, 1.0 mhz, and 10mhz. This can be used directly to
calibrate the receiver and also to calibrate the signal
generator. If you don't have these tools perhaps you can
borrow them.
If the IF transformers are near the limit of their
adjustment, and you know the test frequency is correct, its
probable the resonating capacitors have drifted in value. I
believe this receiver uses permeablility tuned IF coils
(asjustable dust cores).
Again, since the problem seems to be isolated to two
bands and at least one band works OK I think the IF is not
at fault, or at least not the main cause of trouble. I
suggest checking the wiring of the tuning capacitor again to
make sure its OK. You might want to check the other
capacitors in the oscillator and RF stage. I am suspicious
of the oscillator because you say it quits near the low end
of one band. That sound to me like a bad coupling capacitor
there. If you have access to a good RF voltmeter or
reasonably wide band oscilloscope you can check the output
of the oscillator. Even a pick-up loop will show if the
output is varying a lot or if the LO is quitting at the low
end of a band.
Just some things to look for. Remember, this RX is more
than fifty years old so it may have a lot of tired parts (so
do I).


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

hallicrafters s-40a, bad band(s)
 

"ablebravo" wrote in message
ups.com...
thanks again, richard. i am printing this whole train out
to go down
everyone's checklists. yes, i have an eico sig gen,almost
as old as
the set. i check it against an aor 8200 scanner set for
the target
freq at each alignment. it is usually really close to
right on the
money. have an old tek 465b 200mhz, which is still
something of a
mystery, but i can use it in simple ways. i think i can
find the
output. tube-tested the mixer/osci tube itself, and again
got ok.

have also an eico signal tracer, but have only read a bit
about how to
use.

i do plan to check the tuning cap wiring. i did redo the
solder
joints, and while i did photo and mark the wires as the
old came out, i
could have made a mistake. it should be easy to undo and
jumper to
check -- mistake would have to be in center gang area.
wires not long
enough to grossly change where they go.
it will take me a while to go thru all this -- thank you
all.
ab

Richard Knoppow wrote:
"ablebravo" wrote in message
ups.com...
thx richard. esp on how to test the coils. i will do

Long thread snipped...

If you need a handbook for the Tek 465-B there is one on
the BAMA site at:
http://bama.sbc.edu/tektroni.htm
And for Eico instruments at:
http://bama.sbc.edu/eico.htm

This is a very good site to bookmark.

The signal tracer is a wide band amplifier with a
detector on it. You can probe around in the circuit to find
out what is there. That and the scope are powerful tools for
analysing exactly this sort of problem. You can use the
scope with either a high impedance probe or a simple pick-up
loop to look at the oscillator output. The look will cause
the least disturbance to the circuit you are measuring.


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

hallicrafters s-40a, bad band(s)
 

i think you have nailed at least part of it -- rf stage. i have
emailed you offline details. had a completely dead rf amp tube, ahead
of the IF stage. this apparently forced a pretty severe tuning
compensation that affected the bands (?). all tubes tested before
starting work, but this one croaked sometime during repairs. found
intermittent black speaker lead and fixed. was cutting out also. so
there's some of it. already better w/if and bfo align redone. will
see what gives after i finish all rf again... hopefully it will come
back into line on all bands. yes i go first to bama for all.
bookmarked on about 4 computers i have.
ab


Richard Knoppow wrote:
"ablebravo" wrote in message
ups.com...
thx richard. esp on how to test the coils. i will do

Long thread snipped...

If you need a handbook for the Tek 465-B there is one on
the BAMA site at:
http://bama.sbc.edu/tektroni.htm
And for Eico instruments at:
http://bama.sbc.edu/eico.htm

This is a very good site to bookmark.

The signal tracer is a wide band amplifier with a
detector on it. You can probe around in the circuit to find
out what is there. That and the scope are powerful tools for
analysing exactly this sort of problem. You can use the
scope with either a high impedance probe or a simple pick-up
loop to look at the oscillator output. The look will cause
the least disturbance to the circuit you are measuring.


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

hallicrafters s-40a, bad band(s)
 

all tubes tested before starting work, but this one
croaked sometime during repairs.

I just picked up on this thread and read it with interest. Sounds like
you're on the right track. That's a nice receiver when working correctly.

One thing I'm beginning to appreciate about fixing old radios & TVs is that
some components which test "good" or seem acceptable at first, may decide to
give out after a few more hours of operation. The tube (or whatever) may
simply have reached the end of its service life, or perhaps it croaked after
running at full power for the first time in decades.

Before I declare victory on any project, I run it on the workbench for some
hours. Much better to find and correct those latent issues now, rather than
later.

Have fun,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

hallicrafters s-40a, bad band(s)
 

"Phil Nelson" wrote in message
...
all tubes tested before starting work, but this one
croaked sometime during repairs.

I just picked up on this thread and read it with interest.
Sounds like you're on the right track. That's a nice
receiver when working correctly.

One thing I'm beginning to appreciate about fixing old
radios & TVs is that some components which test "good" or
seem acceptable at first, may decide to give out after a
few more hours of operation. The tube (or whatever) may
simply have reached the end of its service life, or
perhaps it croaked after running at full power for the
first time in decades.

Before I declare victory on any project, I run it on the
workbench for some hours. Much better to find and correct
those latent issues now, rather than later.

Have fun,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Its possible for tubes to have bad seals or very slight
cracks that allow some air to get in. The "getter", which is
the silver stuff on the inside, can absorb only so much air
after which the tube will simply not operate. Sometimes the
symptom is a blue glow inside the tube, something like the
glow in a voltage regulator tube. This should not be
confused with the slight dark blue glow somtimes seen in
beam power tubes with very high voltage on the plates. This
is not due to air and is normal.
It is also pretty common for resistors and, especially
capacitors, to die after being unused for a long time. There
are many causes, moisture absorption and others. Even
transformers may die shortly after being fired up after
being unused for a long time.
A useful tool when working on old equipment is a metered
variable transformer. Ideally, it should have both a voltage
and current meter on the output. The current meter is
especially important since it will show excessive current
before damage is done. My suggestion is to remove rectifier
tubes from the equipment and bring it up slowly on the
transformer. If there is any sign of excessive current turn
it off immediately. If it looks OK this way try again with
the rectifiers, again bringing the voltage up slowly. Of
course, the filter capacitors should be checked first for
shorts.
Most electronic equpment likes to run. Leaving it off and
in storage for long periods is not good for it. I suspect
nearly everyone who follows this group already knows all
this stuff.


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

hallicrafters s-40a, bad band(s)
 

hi phil -- i have read, reread, and printed a good bit of your site. i
think i actually got the link to this forum there as well. i couldn't
get by w/help of yourself and the others here who are good enough to
invest the time....
ab

Phil Nelson wrote:
all tubes tested before starting work, but this one
croaked sometime during repairs.

I just picked up on this thread and read it with interest. Sounds like
you're on the right track. That's a nice receiver when working correctly.

One thing I'm beginning to appreciate about fixing old radios & TVs is that
some components which test "good" or seem acceptable at first, may decide to
give out after a few more hours of operation. The tube (or whatever) may
simply have reached the end of its service life, or perhaps it croaked after
running at full power for the first time in decades.

Before I declare victory on any project, I run it on the workbench for some
hours. Much better to find and correct those latent issues now, rather than
later.

Have fun,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html