This (less than 1 ohm) "resistor" is just a 1-1/2" long piece of (nichrome?) wire going from R-11 to chassis ground. The low side of the volume control also connects to this junction instead of going directly to chassis ground.
Refer to the top left schematic:
http://www.nostalgiaair.org/PagesByModel/055/M0005055.pdf
:
:This (less than 1 ohm) "resistor" is just a 1-1/2" long piece of (nichrome?) wire going from R-11 to chassis ground. The low side of the volume control also connects to this junction instead of going directly to chassis ground.
:
:Refer to the top left schematic:
:http://www.nostalgiaair.org/PagesByModel/055/M0005055.
See my answer on ARF tonight,
RCWade
::
::This (less than 1 ohm) "resistor" is just a 1-1/2" long piece of (nichrome?) wire going from R-11 to chassis ground. The low side of the volume control also connects to this junction instead of going directly to chassis ground.
::
::Refer to the top left schematic:
::http://www.nostalgiaair.org/PagesByModel/055/M0005055.
:
:
:See my answer on ARF tonight,
:RCWade
Before I get a chance to see ARF tonight, may I guess that, since the xfmr center tap to chassis ground is where you sometime get negative bias for tubes, that there is just enough hum left there to provide an out-of-phase 120 cycle (they didn't call them Hertz back then) hum to cancel out what's left of the in phase hum from the power supply. Never seen it done before, tho.
Lewis
Also In total agreement…. of the injection of low level out of phase AC at the very most sensitive portion of the audio string…
the bottom of the volume control. It just seems to be a somewhat simpler variant of the hum bucking coil on a speaker/ output
transformer line OR the alternative of using a precisely tapped primary winding on an audio output transformer to feed the B+ into
with the bottom end feeding the screen grid.
They must have refined the precise resistance value required … such that minimal cost was minimized by using that sprig of nichrome.
You can also see that there is no bypassing capacitance on that line at all.
I would ask you for some feedback and enlightenment after another CLOSE inspection of that “wire” , as per its gauge and…
if it really is nichrome ? I would be interested in their connective interfacing manner, as you just don’t soft solder nichrome. If
truly nichrome wire, very likely to be micro brazed to another Cu wire or its termination terminal lug / chassis.
If ever running against that situation of trying to further minimizing hum….on a like design of stacked PS unit… I just might try that using a 5 ohm wire wound “buzz” pot shunting a resistor of a bit higher value than needed.
Thus, that would be giving a vernier adjustment to precisely null for the minimum.
Whats an ARF tonight...why not HERE where the question IS...unless that site is trying to enhance its hit counter ?
73's de Edd
Lewis
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:Also In total agreement…. of the injection of low level out of phase AC at the very most sensitive portion of the audio string…
: the bottom of the volume control. It just seems to be a somewhat simpler variant of the hum bucking coil on a speaker/ output
:transformer line OR the alternative of using a precisely tapped primary winding on an audio output transformer to feed the B+ into
: with the bottom end feeding the screen grid.
:
:
:They must have refined the precise resistance value required … such that minimal cost was minimized by using that sprig of nichrome.
:
:You can also see that there is no bypassing capacitance on that line at all.
:
:I would ask you for some feedback and enlightenment after another CLOSE inspection of that “wire” , as per its gauge and…
: if it really is nichrome ? I would be interested in their connective interfacing manner, as you just don’t soft solder nichrome. If
:truly nichrome wire, very likely to be micro brazed to another Cu wire or its termination terminal lug / chassis.
:
:
:If ever running against that situation of trying to further minimizing hum….on a like design of stacked PS unit… I just might try that using a 5 ohm wire wound “buzz” pot shunting a resistor of a bit higher value than needed.
:
:Thus, that would be giving a vernier adjustment to precisely null for the minimum.
:
:
:Whats an ARF tonight...why not HERE where the question IS...unless that site is trying to enhance its hit counter ?
:
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:73's de Edd
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You may be right about the wire not being nichrome wire because yes, now that you mention it, it was very easy to solder to.
And yes it is just a short 1-1/2" loop of about 24 or 26 gauge wire connecting directly from the vol-potentiometer's bottom lug right to a chassis terminal.
As for the the answer also appearing on ARF, it is in response to my similar post that I left there as well.
Not everyone from NA frequents the ARF venue and visa-versa, so often I will post info or questions on both, attempting to tap into a broader base of info & talent.
Seems that NOW that I'm armed with the knowledge of just how this "hum neutralizer" works, I was able to improve the performance.
After recapping and re-aligning this set I had some considerable hum.
I ohmed out the little "wire" and found it to be more accurately measured at about 1/2 ohm.
On the hunch that the out-of-phase feed back may not be enough...I removed the wire.. and replaced it with a regular metal-film 1-ohm precision resistor and the hum all but disappeared!
So testing it again I see that I can jumper around the 1-ohm resistor and the hum is there again.. remove the jumper and the hum is gone!
Terrific now.
So.. I guess back in the day that this was built they would have liked to have used a 1 ohm resistor but I'm sure they had no such degree of accuracy available then.
Accurately ?
I suspect the reading you had came from the probes resistance's. Unless your equipment can accurately read low resistance value and subtract probes value.
Do you have a picture of the wire?
If it's bare cu wiring, you'd need a very thin wire of many inches to get a resistance of 0.5ohm.
Maybe someone replace the original resistor sometime in the past?
Edd is right about the nichrome wire needing brazing.
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:I suspect the reading you had came from the probes resistance's. Unless your equipment can accurately read low resistance value and subtract probes value.
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:Do you have a picture of the wire?
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You think my reading was inaccurate?
Well..Perhaps... but ....I, of course, anticipated the probe resistance considerations.
And so to eliminate the probe resistance errors, I had first shorted my probes together and let the reading settle in at about .4 ohms... then tested the wire resistance and subtracted the difference.
I did that with two different DMMs.
:If it's bare cu wiring, you'd need a very thin wire of many inches to get a resistance of 0.5ohm.
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:Maybe someone replace the original resistor sometime in the past?
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:Edd is right about the nichrome wire needing brazing.