Hi All,
I am fitting a 100 ohm Humdinder pot to my 15w amplifier. Heaters are 6.3v and take just over 2 amps.
Is it okay to twist all three wires together (6.3v pair plus ground) that are going to the three pot terminals, or should I just twist the two outers (6.3vac pair) and leave the ground out of the twist?
Your advice would be appreciated.
Roger
I am fitting a 100 ohm Humdinder pot to my 15w amplifier. Heaters are 6.3v and take just over 2 amps.
Is it okay to twist all three wires together (6.3v pair plus ground) that are going to the three pot terminals, or should I just twist the two outers (6.3vac pair) and leave the ground out of the twist?
Your advice would be appreciated.
Roger
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I don't know that it should. I was just asking the question to you more knowledgable types. Before I wire it in, I was just checking so that I didn't have to do it twice.
The current trough the 100 ohm resistor is much lower than the current trough a tube heater: twisting the wires to the humdinger is not required (but it looks neat). The PRR answer is correct, in practice.
But theoretically, if we want to minimize the totally negligible magnetic field created by the current flow in the 100 ohm pot, the ground wire should be twisted togheter with the 6.3V pair. The goal is to cancel the magnetic field generated by the first conductor of the 6.3V pair with the equal and opposite magnetic field of the second conductor. When the humdinger is turned either fully clockwise or fully counterclockwise, the return conductor is the ground wire; any position inbetween will see some current flowing on the ground wire : it will create a magnetic field that increases the field of one the two 6.3V pair wire and cancels the field of the other wire.
But theoretically, if we want to minimize the totally negligible magnetic field created by the current flow in the 100 ohm pot, the ground wire should be twisted togheter with the 6.3V pair. The goal is to cancel the magnetic field generated by the first conductor of the 6.3V pair with the equal and opposite magnetic field of the second conductor. When the humdinger is turned either fully clockwise or fully counterclockwise, the return conductor is the ground wire; any position inbetween will see some current flowing on the ground wire : it will create a magnetic field that increases the field of one the two 6.3V pair wire and cancels the field of the other wire.
Using a large pot in a convenient location may mean wiring layout requires some caution. It's not just the magnetic field that is of concern when twisting is used, as any capacitance coupling of the heater wires to a nearby sensitive circuit node/wire/part is less likely to cause a net hum leakage in to that particular node when nearby heater wires are twisted. Although the humdinger pot can attenuate hum, it attenuates the sum of all hum contributions and would only discriminate a particular source of hum if it was dominant.