Heater wiring - Coaxial?

Rundmaus · 5th February 2011, 12:06 PM

Hi there,

possibly stupid question that came to my mind last night:

Has anyone ever tried coaxial cable for tube heater wiring? With the outward and return current flowing coaxially, electromagnetic interference should cancel out perfectly.

Of course, the relatively small conductor thickness would require wiring each valve separately instead of daisy-chain.

Stupid idea?

Greetings,
Andreas

jjman · 5th February 2011, 01:48 PM

I'd be concerned with the current capacity of the outer conductor which is usually expected to be merely a shield. Is there ever a max-current spec for that on coax?

Rundmaus · 5th February 2011, 01:52 PM

I don't think there are max specs for the current given anywhere. One probably has to estimate from the cross section of the thin wires the shield consists of. For standard RG58, the outer conductor becomes a quite thick bundle if straightened and twisted together - at least 1-1.5mm² I would guess...

Greetings,
Andreas

Troncones · 5th February 2011, 03:03 PM

What if you used on cable for each side (assuming heater=6.3v) and grounded the shield?

Rundmaus · 5th February 2011, 03:11 PM

From an "inductive" point of view, this would mean large current loops, as forward and return currents would be spatially separated. This is just what the classical "twisted pair" approach tries to avoid...

el156 · 5th February 2011, 04:25 PM

I had an old Telefunken Amp that used shielded wire for the heater supply in the microphone pre-amp. The heaters had AC supply ,and there was no hum....

Doz · 5th February 2011, 04:33 PM

A co-ax is only effective for un-balanced signals, so I suppose it would be good if one side of your heater referenced that way. The idea is (At RF anyway) that current doesn't flow in the screen.

My Mic amp has 70bB gain, AC heaters (referanced at 100 volts) and is silent. It just has a tight twisted pair.

ruffrecords · 5th February 2011, 04:58 PM

You would be better off using a shielded twisted pair. The twisted pair would cancel out the magnetic field (which a coax will not) and the screen connected to the chassis will provide electrostatic screening.

Cheers

Ian

Doz · 5th February 2011, 05:42 PM

Quote:

Originally Posted by ruffrecords

You would be better off using a shielded twisted pair. The twisted pair would cancel out the magnetic field (which a coax will not) and the screen connected to the chassis will provide electrostatic screening.

Cheers

Ian

... just like a shielded mic lead does. Balanced , with electrostatic screen

jrenkin · 5th February 2011, 06:27 PM

Seems like overkill. I hear again and again that folks here at DIY have twisted pair heater wire and no hum. I suspect good twisting and well planned and placed wires is more than adequate and if you have hum, you either have a problem elsewhere, or you didn't twist the wire well enough.

5th February 2011, 12:06 PM	#1
Rundmaus diyAudio Member Join Date: Aug 2005	Heater wiring - Coaxial? Hi there, possibly stupid question that came to my mind last night: Has anyone ever tried coaxial cable for tube heater wiring? With the outward and return current flowing coaxially, electromagnetic interference should cancel out perfectly. Of course, the relatively small conductor thickness would require wiring each valve separately instead of daisy-chain. Stupid idea? Greetings, Andreas

5th February 2011, 03:03 PM	#4
Troncones diyAudio Member Join Date: Dec 2009 Location: Orange County, California.	What if you used on cable for each side (assuming heater=6.3v) and grounded the shield? __________________ The Myth: A hand full of Tubes, Caps, Resistors and Iron and you have an Amp. The Reality: You have self induced Dementia. Newbie.

5th February 2011, 04:33 PM	#7
Doz diyAudio Member Join Date: Jul 2010 Location: Sat Down	A co-ax is only effective for un-balanced signals, so I suppose it would be good if one side of your heater referenced that way. The idea is (At RF anyway) that current doesn't flow in the screen. My Mic amp has 70bB gain, AC heaters (referanced at 100 volts) and is silent. It just has a tight twisted pair. __________________ "To err is human.. to make a real balls-up requires a computer"

5th February 2011, 04:58 PM	#8
ruffrecords diyAudio Member Join Date: Jun 2007 Location: Holt, Norfolk	You would be better off using a shielded twisted pair. The twisted pair would cancel out the magnetic field (which a coax will not) and the screen connected to the chassis will provide electrostatic screening. Cheers Ian __________________ Ian

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5th February 2011, 01:48 PM	#2
jjman diyAudio Member Join Date: Jan 2009	I'd be concerned with the current capacity of the outer conductor which is usually expected to be merely a shield. Is there ever a max-current spec for that on coax?

5th February 2011, 01:52 PM	#3
Rundmaus diyAudio Member Join Date: Aug 2005	I don't think there are max specs for the current given anywhere. One probably has to estimate from the cross section of the thin wires the shield consists of. For standard RG58, the outer conductor becomes a quite thick bundle if straightened and twisted together - at least 1-1.5mm² I would guess... Greetings, Andreas

5th February 2011, 03:11 PM	#5
Rundmaus diyAudio Member Join Date: Aug 2005	From an "inductive" point of view, this would mean large current loops, as forward and return currents would be spatially separated. This is just what the classical "twisted pair" approach tries to avoid...

5th February 2011, 04:25 PM	#6
el156 diyAudio Member Join Date: Apr 2010 Location: ALBUFEIRA ;PORTUGAL	I had an old Telefunken Amp that used shielded wire for the heater supply in the microphone pre-amp. The heaters had AC supply ,and there was no hum....

5th February 2011, 06:27 PM	#10
jrenkin diyAudio Member Join Date: Nov 2007 Location: Denver, Colorado	Seems like overkill. I hear again and again that folks here at DIY have twisted pair heater wire and no hum. I suspect good twisting and well planned and placed wires is more than adequate and if you have hum, you either have a problem elsewhere, or you didn't twist the wire well enough.

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