|
After running out of things to do I decided to put the S-120 under the 'scope to try to find out where the noise is coming from.? I think I have at least the symptom of something identified.? The first scope trace attached to this post is From T6 Pin 1, with BFO fully CW.? It appears to have a 60 Hz component but not sure, so far, where it is coming from.
73,
--
Justin B.
KI5GKD
|
Are the pulses from a marker or part of the signal? If a marker it
does look like there is some hum on the signal. Have you pushed the
wires around to see if its coupling from wire dress?
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On 11/22/2023 9:24 AM, Justin Bowser - KI5GKD wrote: After running out of things to do I decided to put the S-120 under the
'scope to try to find out where the noise is coming from.? I think I
have at least the symptom of something identified.? The first scope
trace attached to this post is From T6 Pin 1, with BFO fully CW.? It
appears to have a 60 Hz component but not sure, so far, where it is
coming from.
73,
--
Justin B.
KI5GKD
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Hmmm… are you in a rural area? Farms, electric fence? Looks like an electric fence sounds to me!
Dan
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On Nov 22, 2023, at 4:01 PM, Richard Knoppow <1oldlens1@...> wrote:
?Are the pulses from a marker or part of the signal? If a marker it does look like there is some hum on the signal. Have you pushed the wires around to see if its coupling from wire dress? On 11/22/2023 9:24 AM, Justin Bowser - KI5GKD wrote: After running out of things to do I decided to put the S-120 under the
'scope to try to find out where the noise is coming from.? I think I
have at least the symptom of something identified.? The first scope
trace attached to this post is From T6 Pin 1, with BFO fully CW.? It
appears to have a 60 Hz component but not sure, so far, where it is
coming from.
73,
--
Justin B.
KI5GKD
-- Richard Knoppow Los Angeles WB6KBL SKCC 19998
|
I am lost as to what has been done and or checked It appears to have a steady HF signal ?riding on? a very strange, largely pulsed? 60hz? , no idea what t6 is but? perhaps? he means the bfo?? in which case the HF part is expected.? I wonder if that 60Hz waveform is coming from? “anywhere” , but my guess is that the pulse generation is close by? because the rise times look very short No idea ?what happens with no bfo or a bit of bfo ? ? If this was some strange signal from outside we would expect other receivers to so have some similar noise ? Best guess is that 60 hz is “leaking” into the bfo? and triggering ??that pulse somehow??? ?a cap or tube are the first likely things … but it is a strange waveform ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Richard Knoppow
Sent: Wednesday, November 22, 2023 4:01 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-120 Drone/Hum Revisited? Are the pulses from a marker or part of the signal? If a marker it
does look like there is some hum on the signal. Have you pushed the
wires around to see if its coupling from wire dress?
On 11/22/2023 9:24 AM, Justin Bowser - KI5GKD wrote: After running out of things to do I decided to put the S-120 under the
'scope to try to find out where the noise is coming from.? I think I
have at least the symptom of something identified.? The first scope
trace attached to this post is From T6 Pin 1, with BFO fully CW.? It
appears to have a 60 Hz component but not sure, so far, where it is
coming from.
73,
--
Justin B.
KI5GKD --
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998 -- don??? va3drl
|
I asked about the pulse signal in the pix he sent. I think those
might be calibration signals from the scope and not anything produced by
the receiver. Are these what you mean? There is a sine wave with
something low level riding on it in the pix. Need to know what I am
looking at, only the OP can answer that.
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On 11/22/2023 5:00 PM, don Root wrote: I am lost as to what has been done and or checked
It appears to have a steady HF signal ?riding on? a very strange,
largely pulsed? 60hz? , no idea what t6 is but? perhaps? he means the
bfo?? in which case the HF part is expected.? I wonder if that 60Hz
waveform is coming from? “anywhere” , but my guess is that the pulse
generation is close by? because the rise times look very short
No idea ?what happens with no bfo or a bit of bfo
If this was some strange signal from outside we would expect other
receivers to so have some similar noise
Best guess is that 60 hz is “leaking” into the bfo? and triggering
??that pulse somehow??? ?a cap or tube are the first likely things …
but it is a strange waveform
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Richard ?almost? all my scopes are old CRT ?but those dominant pulses? can’t be markers? IMO ? I guess? we could suggest that there is some sine wave? with a dominant tall and fat squarish pulse at the pos peak? and some other squiggle at the negative peak of the 60Hz all riding along on top of some fair sized steady HF. ? Justin complains of strange hum.? if it drones, it might be because that pulse is not a perfect harmonic , as it is likely triggered at slightly different positions in the waveform by something ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Richard Knoppow
Sent: Wednesday, November 22, 2023 8:17 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-120 Drone/Hum Revisited? I asked about the pulse signal in the pix he sent. I think those
might be calibration signals from the scope and not anything produced by
the receiver. Are these what you mean? There is a sine wave with
something low level riding on it in the pix. Need to know what I am
looking at, only the OP can answer that.
On 11/22/2023 5:00 PM, don Root wrote: I am lost as to what has been done and or checked
It appears to have a steady HF signal ?riding on? a very strange,
largely pulsed? 60hz? , no idea what t6 is but? perhaps? he means the
bfo?? in which case the HF part is expected.? I wonder if that 60Hz
waveform is coming from? “anywhere” , but my guess is that the pulse
generation is close by? because the rise times look very short
No idea ?what happens with no bfo or a bit of bfo
If this was some strange signal from outside we would expect other
receivers to so have some similar noise
Best guess is that 60 hz is “leaking” into the bfo? and triggering
??that pulse somehow??? ?a cap or tube are the first likely things …
but it is a strange waveform --
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998 ? -- don??? va3drl
|
Well, many CRT scopes have marker generators. My ancient Tek scope
has markers, both for time and amplitude.
It is possible the pulses are generated externally but see if you
can isolate them. Not the sort of thing a tube radio is likely to
generate. A drone could be anything, someone else's description of a
sound. Could be harmonics. Waveform does not show strong harmonics. Let
him tell us if he has a marker generator. If not do they appear with the
antenna terminals shorted. Can't guess about someone else's observations.
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On 11/22/2023 5:38 PM, don Root wrote: Richard ?almost? all my scopes are old CRT ?but those dominant pulses
can’t be markers? IMO
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
No marker generator that I know of.? T6 is the second IF transformer but but this seems to be rather widespread in the radio.? I also see evidence of this pattern in the signal on V1 Pin 2 (converter cathode) which I have attached to this post...
The scope traces are synced to AC line to this blip, and underlying waveform look to be 60 Hz.? This is the only radio I have with this home/drone.? The S-200 and S-118 are dead quiet when volume turned fully CCW.
All tubes have been changed and signal checked after each tube change.
I have pushed and prodded the wiring bundles and saw/heard no change.? The only thing that makes any difference is when I ground my scope probe to the floating B-.? When I do that this noise disappears!? Connecting scope ground to chassis does nothing and neither does connecting B- to chassis.
When this is looked at on audio output it is clearly visible and when volume is increased it's pretty much "lost" in the rest of the noise.
73,
--
Justin B.
KI5GKD
|
Justin ??…and if you switch the bfo off:? are the noises still there ?? audible? And visual ? ? RE: The only thing that makes any difference is when I ground my scope probe to the floating B-.? When I do that this noise disappears!? ? I guess that means that both “wires” to the probe are connected to the B minus? so you would expect no trace voltage,? but if the real [audible ] noise also vanishes, that would be strange. ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Justin Bowser - KI5GKD
Sent: Thursday, November 23, 2023 11:33 AM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-120 Drone/Hum Revisited? No marker generator that I know of.? T6 is the second IF transformer but but this seems to be rather widespread in the radio.? I also see evidence of this pattern in the signal on V1 Pin 2 (converter cathode) which I have attached to this post...
The scope traces are synced to AC line to this blip, and underlying waveform look to be 60 Hz.? This is the only radio I have with this home/drone.? The S-200 and S-118 are dead quiet when volume turned fully CCW.
All tubes have been changed and signal checked after each tube change.
I have pushed and prodded the wiring bundles and saw/heard no change.? The only thing that makes any difference is when I ground my scope probe to the floating B-.? When I do that this noise disappears!? Connecting scope ground to chassis does nothing and neither does connecting B- to chassis.
When this is looked at on audio output it is clearly visible and when volume is increased it's pretty much "lost" in the rest of the noise.
73,
--
Justin B.
KI5GKD -- don??? va3drl
|
Richard , according to dictionaries, ?I guess drone and hum are similar they used to say some low frequency pipe organ?? music has a drone ..as I vaguely recall, but I guess drone is not very specific. ? Re: “Waveform does not show strong harmonics.” ?that squarish pulse is a strong indication of harmonics of 60Hz as it really distorts any sine wave ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Richard Knoppow
Sent: Wednesday, November 22, 2023 9:19 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-120 Drone/Hum Revisited? Well, many CRT scopes have marker generators. My ancient Tek scope
has markers, both for time and amplitude.
It is possible the pulses are generated externally but see if you
can isolate them. Not the sort of thing a tube radio is likely to
generate. A drone could be anything, someone else's description of a
sound. Could be harmonics. Waveform does not show strong harmonics. Let
him tell us if he has a marker generator. If not do they appear with the
antenna terminals shorted. Can't guess about someone else's observations.
On 11/22/2023 5:38 PM, don Root wrote: Richard ?almost? all my scopes are old CRT ?but those dominant pulses
can’t be markers? IMO
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
-- don??? va3drl
|
Don,
The "anomaly" is present regardless of BFO setting both in waveform and audio.? If I let the probe "hang" and just connect the ground wire to B- the drone/hum goes away.? I have disconnected the probe from the scope and the drone remains.? The probe must be plugged into the scope.
I'm going to take a break from it for a little while and play with the Zenith TO the XYL brought home the other day. :-)
73,
--
Justin B.
KI5GKD
|
sounds like a small value between the chassis and b- would fix it, or B- and neutral or ground
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Don,
The "anomaly" is present regardless of BFO setting both in waveform and audio.? If I let the probe "hang" and just connect the ground wire to B- the drone/hum goes away.? I have disconnected the probe from the scope and the drone remains.? The probe must be
plugged into the scope.
I'm going to take a break from it for a little while and play with the Zenith TO the XYL brought home the other day. :-)
73,
--
Justin B.
KI5GKD
|
Have you looked at the power supply? If the signal is elsewhere it
may be coming from there. Also look at the filament supply. Very odd,
I've never seen anything like it. BTW, I don't remember if you changed
the rectifier to a silicon diode. Not sure how the rectifier cold cause
this but maybe worth trying changing it.
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On 11/23/2023 8:33 AM, Justin Bowser - KI5GKD wrote: No marker generator that I know of.? T6 is the second IF transformer but
but this seems to be rather widespread in the radio.? I also see
evidence of this pattern in the signal on V1 Pin 2 (converter cathode)
which I have attached to this post...
The scope traces are synced to AC line to this blip, and underlying
waveform look to be 60 Hz.? This is the only radio I have with this
home/drone.? The S-200 and S-118 are dead quiet when volume turned fully
CCW.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
You mean that the "noise" on the radio comes from the scope probe?
An ungrounded probe might cause a hum loop. Is the receiver noisy when
the probe is not connected? That doesn't sound right.
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On 11/23/2023 9:39 AM, don Root wrote: Justin ??…and if you switch the bfo off:? are the noises still there ?
audible? And visual ?
RE: The only thing that makes any difference is when I ground my scope
probe to the floating B-.? When I do that this noise disappears!
? I guess that means that both “wires” to the probe are connected to
the B minus? so you would expect no trace voltage,? but if the real
[audible ] noise also vanishes, that would be strange.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Richard, no, the drone/hum goes away with the probe ground hooked to B-!? The Selenium has been replaced with a diode and the S-200 has the same capacitor stack and 1N4004 and has no hum.? I'm going to refer to it as hum so as to not confuse people...
Scott - Are you talking a small cap?? I've tried several and have made no difference.
73,
--
Justin B.
KI5GKD
|
Yes , I was thinking probe capacitance was reducing the hum, but it seems that you tried it already
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Richard, no, the drone/hum goes away with the probe ground hooked to B-!? The Selenium has been replaced with a diode and the S-200 has the same capacitor stack and 1N4004 and has no hum.? I'm going to refer to it as hum so as to not confuse people...
Scott - Are you talking a small cap?? I've tried several and have made no difference.
73,
--
Justin B.
KI5GKD
|
Justin I am also a bit confused about?? all the conditions when the hum goes silent.? ??The B- it connected to the probe ground .. which is connected to thr scope frame ? which is grounded to the house power ground? …so effectively you have taken B- to earth .? if so, a jumper from ?B- to any real ground should kill the hum? Presumably the AC line cap? and ?the AC to chassis cap ?have been changed ????so we begin to wonder as usually operating? what voltage is b- to earth and chassis to earth and cabinet to earth, and does the pulde show up uf a scope is used rather than a meter?? …. All for some future day ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Justin Bowser - KI5GKD
Sent: Thursday, November 23, 2023 6:04 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-120 Drone/Hum Revisited? Richard, no, the drone/hum goes away with the probe ground hooked to B-!? The Selenium has been replaced with a diode and the S-200 has the same capacitor stack and 1N4004 and has no hum.? I'm going to refer to it as hum so as to not confuse people...
Scott - Are you talking a small cap?? I've tried several and have made no difference.
73,
--
Justin B.
KI5GKD ? -- don??? va3drl
|
Don,
That's what I was thinking at one point so I tied B- to chassis and there was no change in the hum.? All caps have been changed so the B- to chassis cap is new.? Maybe I need to experiment with larger capacitors between B- and chassis, maybe the ones I was trying were too small to pass the 60 Hz component...
The S-120 is up on the shelf for a bit as I have a couple more radios to play with.
73,
--
Justin B.
KI5GKD
|
Justin If you increase the capacitor value from B- to chassis, you increase the shock current available if the chassis inadvertently becomes hot.? The different safety councils of the period limited this capacitor value 0.25uF or less.? In the S-120 it's value is 0.047uF in parallel with a 470k resistor.
How does this hum compare to the hum of other AC/DC radios that you have serviced?? If you can receive a BC station well and the hum is barely noticeable then that is about as good as it gets.? Off station, the radio RF gain is at maximum so the hum should be more noticeable but on station much less noticeable.
If we are still talking about the S-120 and not some other radio, is the Selenium rectifier still installed?? As the Selenium rectifier fails, the foreword and reverse resistances tend to become more similar instead of the normal tens of ohms foreword and several thousands of ohms in reverse.? Refresh my memory, what is the ripple voltage that you measure on the C31 filter capacitor sections A, B and C? Regards, Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Saturday, November 25, 2023 at 12:10:40 AM CST, Justin Bowser - KI5GKD <justin.bowser@...> wrote:
Don,
That's what I was thinking at one point so I tied B- to chassis and there was no change in the hum.? All caps have been changed so the B- to chassis cap is new.? Maybe I need to experiment with larger capacitors between B- and chassis, maybe the ones I was trying were too small to pass the 60 Hz component...
The S-120 is up on the shelf for a bit as I have a couple more radios to play with.
73,
--
Justin B.
KI5GKD
|
Justin My first question/suggestion? was simple; it seemed like the hum quit when you grounded B- via the scope. I cant tell because I don’t know if your scope frame/ cabinet is isolated from the house AC power? or not.?? Anyhow the next test is to take a jumper from B- to the wall outlet ground, and see if the hum quits. The answer might give some clues as to what is going on. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Justin Bowser - KI5GKD
Sent: Saturday, November 25, 2023 1:11 AM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-120 Drone/Hum Revisited? Don,
That's what I was thinking at one point so I tied B- to chassis and there was no change in the hum.? All caps have been changed so the B- to chassis cap is new.? Maybe I need to experiment with larger capacitors between B- and chassis, maybe the ones I was trying were too small to pass the 60 Hz component...
The S-120 is up on the shelf for a bit as I have a couple more radios to play with.
73,
--
Justin B.
KI5GKD ? -- don??? va3drl
|
don Root
Jim Whartenby