Resistive Line Cord ... would it be legal today?

[saddlestone-man]

Hello All

Most of us have spent time finding solutions for replacing the missing or disintegrating line cord on old radios. I was wondering if a cable manufacturer could be persuaded to produce resistive line cord today, would it be legal to sell and use such a product? Are there any similar products used in industry today?

I realise there were different types of cord, but let's just keep the discussion simple, and assume just a single type could be devised that would meet all requirements.

best regards ... Stef

[Radio Wrangler]

Flipping the question around, under which standard would it be certified? I suspect there may not have been one created. There will be one for resistive heating tapes - the sort of thing wrapped around pipes to prevent freezing, but I've had a search for flexible resistive cables and not found anything.

So I think you'd have to get a standard created before getting any cable made.

David

[peter_scott]

The simple solution is to use a capacitive dropper instead of the resistive lead.

Peter

[vinrads]

Capacitive dropper is a good solution if you have room in the set , there are many U.S.A midget sets with little or no room for anything .Mick.

[kalee20]

I seem to remember a friend bringing home from France an inspection lamp based on a fluorescent tube and not much else... And the lead became warm in use so was presumably a resistive ballast. (Dunno how the start-up sequence functioned). This was in the early 1990's, and was new then!

Asbestos as a core obviously wouldn't be used, but glass-fibres would be just as good.

[AC/HL]

There's no point. The only market is us, and the volumes would prohibit any manufacturer tooling up, let alone certification. The short lived excuse of DC mains is long gone and virtually everything is low voltage now. What isn't makes a feature of the transformers.

[Mike. Watterson]

It's possible, but there is no market.

One can be made easily enough using suitable layers of sleeving on resistors. Derate the resistors to 1/4 to allow for the insulation layers, the inner one should be fibre glass. There would also be a steel tape to avoid over bending the lead. The joints between resistor done with braid.

Approval isn't impossible, but there is no market.

[Croozer]

Interesting question. The advances in materials and protection should mean that as a concept, a conductor designed to run warm but not hot could be done easily and safely. At greater scale, insulated power transmission lines are not assumed to run without tempereature change. At domestic scale, electric blankets are still sold - indeed they now may be energised while the bed is occupied!


However, as a design concept, dumping power as heat to acheive a voltage drop for -say -running a 110v appliance from a 240v supply would probably infringe environmental regulations.

All wires are resisitive, I suppose all you need a a few hundred yards to do the job for a 110V set at 240V.

[Julesomega]

Underfloor heating mat is heating cable which is stuck to the floor base layer, it can be bent to shape but it is NOT at all flexible

[broadgage]

I believe that resistive line cord COULD be made today, but probably WONT be for the reasons already given.

The fluorescent inspection lamps with resistive line cord were still made until recently, but I suspect that cheap and compact electronic ballasts killed them off.

[julie_m]

If you are using a capacitive dropper to run a radio, which will draw more power on the half-cycle with the rectifier forward-biased than on the half-cycle with it reverse-biased, then it might be worth wrapping a bridge rectifier around the whole set so as to make the load symmetrical. Note, though, that the chassis would no longer be at Neutral potential; but one diode away from the Line. This should not be a problem in practice, because (1) DC mains were as likely to be positive-neutral as negative-neutral and (2) reversible mains connectors were commonly encountered in those days, so all sets had to be designed on the assumption that the chassis would not be at a safe potential and as a consequence were thoroughly insulated.

[Paul JD]

Originally Posted by merlinmaxwell

All wires are resisitive, I suppose all you need a a few hundred yards to do the job for a 110V set at 240V.

Hmmm lets see.... If we want to drop 130v and we assume our radio pulls 150 mA that needs a resistance of 867 ohms. If our mains cable is 18 AWG (resistance 6.385 ohms per 1000 ft) we will need about 136,000 feet

[julie_m]

Hmmm lets see.... If we want to drop 130v and we assume our radio pulls 150 mA that needs a resistance of 867 ohms. If our mains cable is 18 AWG (resistance 6.385 ohms per 1000 ft) we will need about 136,000 feet [/QUOTE]Yes, but that's still only about 28 miles. (Call it 6.3Ω per 300m., which is 21Ω/km, then 864Ω is 44km. -- that sounds about right. Best order 500 hundred-metre drums, just to be on the safe side.)

[dave walsh]

Oh yes I like those calculations Paul/Julie. Better to be safe than sorry eh

Dave W

[Oldcodger]

Is that Q resistance to slippage or needing a resistance per foot/ length. In Zimbabwe lots of year go ,I was called on do a favour. He was was head of the local transport group ,and I was the local signal tech, given permission to foster good relations between departments, particularly transport and electrics, with no problems
Problem was that the tuning cord on his wife's favourite radio had broken and none could be found. My solution was to use a length of strip wire from a telecomms cable. Fixed and we had a happy wife . On the other side- I've no answer.

[Herald1360]

Why use 18 AWG for a radio mains lead? 24AWG would be adequate. Go for PTFE or silicon rubber insulated to allow it to run fairly hot on the reel. Up to about 160R per km round trip so the numbers are less silly.

Actually ordinary PVC would probably be OK at half an amp.

[Oldcodger]

Sorry ,folks, ignore my last post. I was looking at tuning cord vs anything else.

[crackle]

Would this sort of thing work https://eltherm.com/en-gb/products/h...s/details-elk/

Mike

[Leon Crampin]

Just take an electric blanket to bits.....

Usual safety caveats which we all understand, but I repaired an American midget this way in my youth - very effectively.

Leon.