All,

I just finishing re-capping a Hallicrafters SX-42 I bought recently.
Thanks Phil for an excelent web site (http://antiqueradio.org/) and
big help. This is my first restoration of such complex communications
receiver. I did restore a Fisher KX-200 and X-202-B amps, a Sansui
320 receiver and a few smaller radios. The rig was in excelent
condition and after re-capping and cleaning up the contacts the AM and
shortwave bands worked great...

.... but the FM is completely silent. When I move the band switch to
the upper 2 bands I can hear static in the AM reception and silence
when I switch to FM. Does this preclude any problem with the
bandswitch? I inspected the bandswitch and the wafers look very clean
and don't show any signs of carbonization.

I cleaned and inspected the reception switch as well and it seems OK.
All tubes check fine and voltages are as they should be.

I'll continue investigating the problem but any suggestions are
greatly appreciated.

Thanks.
--
Elias

"Mazur" wrote in message
om...
All,

I just finishing re-capping a Hallicrafters SX-42 I bought recently.
Thanks Phil for an excelent web site (http://antiqueradio.org/) and
big help. This is my first restoration of such complex communications
receiver. I did restore a Fisher KX-200 and X-202-B amps, a Sansui
320 receiver and a few smaller radios. The rig was in excelent
condition and after re-capping and cleaning up the contacts the AM and
shortwave bands worked great...

... but the FM is completely silent. When I move the band switch to
the upper 2 bands I can hear static in the AM reception and silence
when I switch to FM. Does this preclude any problem with the
bandswitch? I inspected the bandswitch and the wafers look very clean
and don't show any signs of carbonization.

Did you ever hear the FM working?

Does the second to top band work?. This is something like 27 to 60 Mc, if I
recall. There's usually some paging service noise or maybe a cab company
or something there This band also uses the 10.7 Mc IF section.

In the AM position, you say you can hear static. Do you hear any FM
stations in the FM band? The AM detector should detect FM stations, using
the frequency slope of the IF transformers.

It's very easy to test the radio's local oscillator. In the FM position,
the oscillator runs either 10.7 Mc above or below the signal frequency. It
could be either, and I forget which. Another FM radio can pick up the
oscillator signal. Tune the second radio to, say, 90 Mc. Tune the SX-42
around 79 and 101 Mc. Somewhere around one of those frequencies, you should
get what sounds like a dead carrier. If the top band oscillator section is
misaligned, the actual indicated frequencies could be different.

If your oscillator seems dead, a 7F8 which doesn't want to oscillate at FM
frequencies is a possibility, but I'm suspicious of locktal sockets and
pins, and a good cleaning might be in order.


I cleaned and inspected the reception switch as well and it seems OK.
All tubes check fine and voltages are as they should be.

I'll continue investigating the problem but any suggestions are
greatly appreciated.

Thanks.
--
Elias

"Mazur" wrote in message
om...


By the way, the RF amps are also a possibility, but they don't head up the
list. One of the RF amps on my SX-62 went to sleep, and I hardly noticed.
If every thing else is working well, this radio has a fair amount of reserve
gain. I could pull both RF amp tubes, and the radio would still hear FM
stations OK, as long as I had a wire on the antenna terminals. Didn't need
a wire with the all the tubes in.

Frank Dresser

Hi Frank,

Thanks for the reply. I did test the local oscilator and it seems to
be working fine. I could clearly hear a dead carrier at the frequency
range you mentioned.

No, I was never able to hear the FM. Also in AM mode I can't detect
any FM station at all. I'll keep on looking.

Thanks.
--
Elias


"Frank Dresser" wrote in message ...
"Mazur" wrote in message
om...
All,

I just finishing re-capping a Hallicrafters SX-42 I bought recently.
Thanks Phil for an excelent web site (http://antiqueradio.org/) and
big help. This is my first restoration of such complex communications
receiver. I did restore a Fisher KX-200 and X-202-B amps, a Sansui
320 receiver and a few smaller radios. The rig was in excelent
condition and after re-capping and cleaning up the contacts the AM and
shortwave bands worked great...

... but the FM is completely silent. When I move the band switch to
the upper 2 bands I can hear static in the AM reception and silence
when I switch to FM. Does this preclude any problem with the
bandswitch? I inspected the bandswitch and the wafers look very clean
and don't show any signs of carbonization.

Did you ever hear the FM working?

Does the second to top band work?. This is something like 27 to 60 Mc, if I
recall. There's usually some paging service noise or maybe a cab company
or something there This band also uses the 10.7 Mc IF section.

In the AM position, you say you can hear static. Do you hear any FM
stations in the FM band? The AM detector should detect FM stations, using
the frequency slope of the IF transformers.

It's very easy to test the radio's local oscillator. In the FM position,
the oscillator runs either 10.7 Mc above or below the signal frequency. It
could be either, and I forget which. Another FM radio can pick up the
oscillator signal. Tune the second radio to, say, 90 Mc. Tune the SX-42
around 79 and 101 Mc. Somewhere around one of those frequencies, you should
get what sounds like a dead carrier. If the top band oscillator section is
misaligned, the actual indicated frequencies could be different.

If your oscillator seems dead, a 7F8 which doesn't want to oscillate at FM
frequencies is a possibility, but I'm suspicious of locktal sockets and
pins, and a good cleaning might be in order.


I cleaned and inspected the reception switch as well and it seems OK.
All tubes check fine and voltages are as they should be.

I'll continue investigating the problem but any suggestions are
greatly appreciated.

Thanks.
--
Elias

"Mazur" wrote in message
om...
Hi Frank,

Thanks for the reply. I did test the local oscilator and it seems to
be working fine. I could clearly hear a dead carrier at the frequency
range you mentioned.

No, I was never able to hear the FM. Also in AM mode I can't detect
any FM station at all. I'll keep on looking.

Thanks.
--
Elias



]Is there any reception on the low VHF band? If the expected signals come
in there, it would indicate your IF sections are OK. In that case the mixer
circuit would be a good suspect.

Do you have the schematic? I think there's one online at the Boatanchor
Manual Archive. There's also a couple of regular vendors on ebay who sell
nice quality reproduction manuals.

Do you have a signal generator? As Peter suggested, that's the next step.

Frank Dresser

I have an SX-42 waiting to be resurrected (it works, but I'm leary of
turning it on much). Does anyone have a list of caps to "recap" it,
so I can do the shopping easily?

I understand that "recapping" it is almost a necessity to keep it
going, since a bad cap can damage other parts to the point of
writeoff.

73, doug

Frank Dresser wrote:

"Mazur" wrote in message
om...

Hi Frank,

Thanks for the reply. I did test the local oscilator and it seems to
be working fine. I could clearly hear a dead carrier at the frequency
range you mentioned.

No, I was never able to hear the FM. Also in AM mode I can't detect
any FM station at all. I'll keep on looking.

Thanks.
--
Elias




]Is there any reception on the low VHF band? If the expected signals come
in there, it would indicate your IF sections are OK. In that case the mixer
circuit would be a good suspect.

Do you have the schematic? I think there's one online at the Boatanchor
Manual Archive. There's also a couple of regular vendors on ebay who sell
nice quality reproduction manuals.

Do you have a signal generator? As Peter suggested, that's the next step.

Frank Dresser


I can only offer a personal observation from many years ago (1964-ish)
when the SX-42 caps were still expected to be fresh. My Elmer lent me
(me=an 11-year old...they don't make Elmers like that anymore) his SX-42
to use over Xmas vacation. Of course I didn't hook up anything special
for a VHF antenna and all I got was a slight whisper from 3 of the 4 FM
stations in town. I kinda figured then that this radio was pretty deaf
up at that end of its range although the local paging system on about 35
Mc boomed thru.
I've never heard anything to the contrary.

-Bill

".Bill" wrote in message

I can only offer a personal observation from many years ago (1964-ish)
when the SX-42 caps were still expected to be fresh. My Elmer lent me
(me=an 11-year old...they don't make Elmers like that anymore) his SX-42
to use over Xmas vacation. Of course I didn't hook up anything special
for a VHF antenna and all I got was a slight whisper from 3 of the 4 FM
stations in town. I kinda figured then that this radio was pretty deaf
up at that end of its range although the local paging system on about 35
Mc boomed thru.
I've never heard anything to the contrary.
================================================
Bill:

I don't think your experience is typical. I currently have one SX-42
and two SX-62A receivers on hand and they all perform very well on FM.
When tuned up and working well, the SX-42 is a very sensitive
receiver on all bands.

Best Regards,

Ed
Canyon Lake, TX

Pete,

Thanks for the reply. I just bought a signal generator and should be
receiving it shortly so I can test it.

I did check the LO and it works fine.

I checked all voltages as listed on the service manual and they match
fine except the voltages on the discriminator tube. They list as 0.25
volts on pins 3 and 5 (I believe) but they are actually showing as
-0.25V. I don't know if that has anything to do with it. Could it be
one of the capacitors in the discriminator coil unit?

Will keep looking....

Thanks.
--
Elias


" Uncle Peter" wrote in message news:0AySc.13831$Yf6.7407@lakeread03...
"Mazur" wrote in message
om...
All,

I just finishing re-capping a Hallicrafters SX-42 I bought recently.
Thanks Phil for an excelent web site (http://antiqueradio.org/) and
big help.

If the FM is dead, two things too check as a start: First, see if you
can force a 10.7 MHz signal through the IF stages. In the SX-42, the
AM 455kHz IF amps also double as 10.7 MHz IF stages and
utilize 455kHz and 10.7 MHz IF cans in series. On FM, there are
two additional 10.7 IF (limiter stages) before the FM detector as
well. You could also inject audio at the output of the FM detector
to verify that the audio paths are working in that mode.
If the IF stages are all working and passing a 10.7 MHz signal,
I'd verify that the LO is working on the FM band.

This should be an easy problem to isolate using signal injection
or signal tracing.

Pete

"Mazur" wrote in message
m...
Pete,

Thanks for the reply. I just bought a signal generator and should be
receiving it shortly so I can test it.

I did check the LO and it works fine.

I checked all voltages as listed on the service manual and they match
fine except the voltages on the discriminator tube. They list as 0.25
volts on pins 3 and 5 (I believe) but they are actually showing as
-0.25V. I don't know if that has anything to do with it. Could it be
one of the capacitors in the discriminator coil unit?

Will keep looking....

Thanks.
--
Elias



Don't worry about your discriminator. Your AM detector is working at 455 kc
and should also be working at 10.7 mc. If you aren't hearing any signals
with the AM detector then that almost certainly means the signals aren't
getting to the AM detector.

Frank Dresser

..