sears-roeb: Silvertone 4665

I have several wires that I can't find replacements for.  It's a 20 gauge stranded, insulated, then wrapped in a solid core wire, finally wrapped in cloth.  Other than this outer wire being used as a jumper, are there any other' characteristics?  What can I use as a replacement?  Can I wrap a cloth covered wire and then shrink wrap it?

Signed,

lcenotto

• 22 Gauge Jacketed Wire (18 KB)

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Early radio wire was cloth-covered: rubber would not take the heat.

Cloth-covered wire is often easy to strip: just push the cloth back.

Modern wire uses modern tough plastics.

There was a transitional period with cloth over plastic. I do not know why. Maybe they did not trust their plastic?

There should not be any significant electrical difference. It is all about historical looks.

Plain cloth-covered can be bought here:

Hoffman (guitar) Amps, cloth wire - There's no official rating on this stuff; but it has been used in many hot tube guitar amplifiers at voltages higher than most radios and many TV sets (not counting the sparkplug-type wire used for the 20,000V line).

Antique Electronic Supply - has cloth over plastic with UL rating. It is said to be hard to strip.

Sundial Wire - has cloth-covered plastic wire in 22 to 12 gauge and many designer colors (gold, no yellow), suitable for wall-cord (and maybe speaker) wire replacement. Note: their "cord" is often modern black-white-green triplet with a cloth sleeve. Single-conductor seems to be just black, gold, and silver cloth down to 18ga.

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Paul,

Thank you for your response to my inquiry.  However, all three sites you mentioned do not have the type of wire I'm looking for.  The picture didn't capture all the details.  It's 20 gauge wire covered with an insulator.  This insulator is then wrapped tightly around, and it is covered with a lacqured covered cloth.  One end of this coiled is connercted to ground.  I have searched many different web sites and come up with nothing.  Any ideas?

Lee

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> insulated, then wrapped in a solid core wire, finally wrapped in cloth.

Ah. This is a variation of a low-cost "shielding" technique. Hi-Fi sets often need some shielded leads, but do not go to the expense and trouble of full braided shield. Instead a bare ground wire is wrapped around a signal wire. This gives 20%-80% shielding, instead of the 99% of full braid, but is cheaper and easier and often ample. Also the lesser shielding is lower stray capacitance.

I have never seen it with an additional layer of cloth. By the time this is done, cost must approach the price of pre-made braided-shield cable? However the factory may have had bare-wire and cloth sleeve handy.

What is the function of these wires? As far as I can tell by the schematic, shielding is used for detector diode, detector to volume control, and volume to first audio grid. Since these wires run across the chassis near AC, DC, and audio power nodes, they need shielding-- else there could be low buzz or even howling. As a practical repair, common inexpensive wrap-shield wire will work fine.

"Mini shielded cable RG174" (Hoffman and others) is compact, "too good", a bit hard to work with. RadioShack 278-513 is readily available, affordable ($10 will do two dozen radios), almost too easy to work with (a bit fragile), and the plastic melts too easily when soldering. I use it; I don't like it. The 278-513 has two inside conductors; ignore one. 

All this stuff is objectionable for "authentic restoration": modern plastics in a vintage cloth-wire set. However you indicated that shrink-tube was acceptable. If so, any of these pre-made shielded cables will be a better job.

If cloth is desired, you can try to find cloth sleeve to go over cable (or a hand-wound recreation of the original construction). Antique Electronic Supply has fiberglass sleeve in two sizes: fireproof, but the bright white will stand-out as "new!". You may do better going to a fabric store, some brik-a-brak and piping is hollow braid.

If this is not in the audio section but in the RF/IF section, then the exact capacitance may be critical, it may have to be same wire, cloth, and any wax impregnant, to hit the same tuning.

Are you sure the wire has to be replaced?

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Paul,

Once again, thanks.  Yes, both of them have to be replaced.  The inner insulator is so brittle that it falls apart if you touch it.  I've made satisfactory replacements myself, but don't like the shrink tubing.  Doesn't allow for much flexibility.  If I'm reading the schematic correctly, only one end is connected to ground.  Is this a method of reducing interference?  I could always retoute thereby reducing the need for shielding.  What do you think?

Lee

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I forgot to say: a cheap source for small shielded audio cable is old RCA hi-fi phono cables. Maybe you have a box of cables behind the hi-fi? They typically go bad because the connectors are junk; no problem since you will be cutting them off.

> reroute thereby reducing the need for shielding.  What do you think?

I think if there was a better route, the prototype de-bugger would have done that instead of going to the extra trouble and expense of shielding. Therefore I doubt there is a better route.

> If ... only one end is connected to ground. 

That would be quite reasonable. The audio return path is through chassis or via power return conductors. The shield is only to divert stray interference. Connecting shield at both ends would be a Ground Loop, which is sometimes bad news, and more work anyway. 

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Paul,

Excuse my questions.  I'm fairly new at this and don't understand everything.  Which brings me back to my original concern.  Where can I get the wire I need? 

Lee

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