RadioBanter - sx-42 s meter problem

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sx-42 s meter problem

In article ,
"clive & kristi ingram" wrote:

hi. i've got a hallicrafters sx-42 that has developed a strange s meter
problem.the receiver works on all bands but the s meter works normaly only
on the first 2 bands,broadcast band and band 2 (1.6 to 5 mc). when I switch
to band 3 (5
to 15 mc) and bands 4, 5 and 6 i hear signals but the s meter indicates
zero. occasionally
there will be a very slight negative indication with the needle moving below
the zero. it
must be getting ok avc on the first 2 bands but not on the others. does
anyone have any
suggestions?

ci-

My understanding is that the S-Meter is measuring a negative voltage
(AGC) that is developed at the AM detector, and is used to limit the
amplification of an earlier stage.

For the meter to read down-scale, there could be either a vacuum tube
that is "soft" or a DC Blocking capacitor that is leaking. You may find
a tube that has positive voltage on its control grid. That could either
be caused by the tube or the capacitor that feeds it.

Fred
K4DII

sx-42 s meter problem

Fred McKenzie wrote:
In article ,
"clive & kristi ingram" wrote:

hi. i've got a hallicrafters sx-42 that has developed a strange s meter
problem.the receiver works on all bands but the s meter works normaly only
on the first 2 bands,broadcast band and band 2 (1.6 to 5 mc). when I switch
to band 3 (5
to 15 mc) and bands 4, 5 and 6 i hear signals but the s meter indicates
zero. occasionally
there will be a very slight negative indication with the needle moving below
the zero. it
must be getting ok avc on the first 2 bands but not on the others. does
anyone have any
suggestions?

ci-

My understanding is that the S-Meter is measuring a negative voltage
(AGC) that is developed at the AM detector, and is used to limit the
amplification of an earlier stage.

For the meter to read down-scale, there could be either a vacuum tube
that is "soft" or a DC Blocking capacitor that is leaking. You may find
a tube that has positive voltage on its control grid. That could either
be caused by the tube or the capacitor that feeds it.

Fred
K4DII
Yes but the meter reads correctly on two bands so the tubes / capacitors
must still be ok. It's possible that there are capacitors tied to
specific coils that get switched between bands, but my bet would be that
you have a high resistance contact on the band switch. Get some switch
cleaner spray and have a go at that switch. After spraying the contacts
rotate the switch back and forth around the bad positions to get the
cleaner to do it's work. Also check the coils for an open winding, or a
bad solder joint that has gone high resistance between the coil and the
band switch.

sx-42 s meter problem

"clive & kristi ingram" wrote in
message
m...
hi. i've got a hallicrafters sx-42 that has developed a
strange s meter
problem.the receiver works on all bands but the s meter
works normaly only
on the first 2 bands,broadcast band and band 2 (1.6 to 5
mc). when I switch to band 3 (5
to 15 mc) and bands 4, 5 and 6 i hear signals but the s
meter indicates zero. occasionally
there will be a very slight negative indication with the
needle moving below the zero. it
must be getting ok avc on the first 2 bands but not on the
others. does anyone have any
suggestions?
73 ci

I am not sure the S-meter measures AVC action directly.
On my Hallicrafters (and other) receivers it measures
cathode or plate current in some tube. These meters are
usually reversed, i.e., when off the pointer goes to the
right (high end) of the scale. The meter in the SX-42 is
switched and also acts as a tuning meter for FM. It also
appears to be switched for different bands but the
schematics are confusing and I have not traced out the meter
circuit.
Check the tube socket voltages and resistances for a
start. Also, it should be obvious if the AVC is working or
not regardless of the meter.
The SX-42 is notoriously difficult to work on so I wish
you success and a good supply of patients.

--
Richard Knoppow
Los Angeles
WB6KBL

sx-42 s meter problem

thanks to you fred, ken and richard for your help. looks like contact
cleaner on the band switch and/or
a quickie alignment on the rf section fixed the problem. really appreciate
you knowledgeable guys' help.

ci

sx-42 s meter problem

hi. i've got a hallicrafters sx-42 that has developed a strange s meter
problem.the receiver works on all bands but the s meter works normaly only
on the first 2 bands,broadcast band and band 2 (1.6 to 5 mc). when I switch to
band 3 (5
to 15 mc) and bands 4, 5 and 6 i hear signals but the s meter indicates zero.
occasionally
there will be a very slight negative indication with the needle moving below
the zero. it
must be getting ok avc on the first 2 bands but not on the others. does anyone
have any
suggestions?
73 ci

A possibility is that, due to a failure affecting the receiver circuitry
somewhere, your receiver has become extremely deaf on band 3 and up, so that
even the strongest signals do not move the S-meter, though they can still be
heard.

The fact that the S-meter gives a very slight negative indication may not mean
much, as it could just be a consequence of the same failure that makes the
receiver deaf on bands 3 and up.

You must exercise your judgement to determine whether on bands 3 and up the
problem is just in the fact that the S-meter does not move or that the receiver
instead becomes deaf. For this purpose, you could try to tune the same station
on the highest part of band 2 and in lowest part of band 3 (the two bands will
surely overlap somewhat) and, without looking to the S-meter, try to determine
whether the receiver sensitivity looks similar.

73

Tony I0JX
Rome, Italy