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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 23rd Jun 2021, 11:00 am   #1
Richardgr
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Default Braided cables in 1930's radio

As I explained to my other half, these two 30's radios just appeared overnight in my collection one day. They were both original and pretty tatty; I have documented some of the investigations I have done on the Radio forum, under 'Paillard 768'.

I am using them to get a better understanding of restoring this type of device, and am finding that some of the design tricks used back then were very clever. For instance, using the voice coil for smoothing *and* negative bias of the output tube.

Both of these Paillards I have (the other is a slightly later 70TR) make quite extensive use of braided wires, soldered to the chassis and each other, and traversing the chassis.

I can see that the wire core is rubber insulated. This has hardened with age and exposure to ozone, and if I disturb the exposed wire it cracks the insulation.

I will try not to disturb them, but one option would be to extract them, feed PVC wire inside, and replace, only soldering when there is no wire inside, or at the ends. I presume it would be difficult to extricate the old rubber coated wires.

Alternatively, since later radios don't use them so much, and I notice that the second, later Paillard, relies on this approach less, can they be left in place and circumvented, maybe considering the grounding scheme at the same time?

These radios will be restored using new components under the chassis, leaving the top of the chassis unchanged. I am not looking for originality here, but giving them a new lease of life, and in order to experience the performance of the tubes and the voice coil speaker.

What do others do?
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Old 23rd Jun 2021, 11:19 am   #2
ms660
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Default Re: Braided cables in 1930's radio

Quote:
Originally Posted by Richardgr View Post
I am using them to get a better understanding of restoring this type of device, and am finding that some of the design tricks used back then were very clever. For instance, using the voice coil for smoothing *and* negative bias of the output tube.
That method of obtaining a bias voltage or voltages from across the loudspeakers field coil is also known as "back bias" Sometimes resistors were used instead in various makes of receiver.

Lawrence.
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Old 23rd Jun 2021, 12:36 pm   #3
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Default Re: Braided cables in 1930's radio

I'm guessing you could sever and then pull through the inner wires of those coaxials. I realise (like yourself) that they may crumble, nonetheless I reckon you should be able to pull them though. In any case, even if they don't come out complete, all is not lost, you can push the new wires through, hoping that they will push out any debris, or just replace the whole coax wire with new stuff. I suspect the rubber crumbling is likely to be more affected by side to side movement than linear pulling.
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Old 23rd Jun 2021, 4:44 pm   #4
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Default Re: Braided cables in 1930's radio

Try using the old inner as a pull through for the new wire. That should clear out any "crumbliness" as it goes.
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Old 23rd Jun 2021, 8:47 pm   #5
M0FYA Andy
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Default Re: Braided cables in 1930's radio

You can usually push the braid back causing it to become shorter and fatter, removing the old inner and installing a new one is then easy, followed by pulling the braid back to its original length.

Andy
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Old 23rd Jun 2021, 9:09 pm   #6
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Default Re: Braided cables in 1930's radio

I would try to leave the screened cables in place unless they are shorting internally.

The crumbly sections at the end could be covered in heat shrink tubing.

Are they carrying a high voltage supply or a low voltage signal?
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Old 25th Jun 2021, 5:52 pm   #7
Richardgr
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Default Re: Braided cables in 1930's radio

I think they are mainly passing signals back and forth, it is not the most sensible design. I will do my best to not disturb anything, and see whether I get away with it.

As mentioned, they are not going to be collectable, so it is more of a learning exercise for me. Maybe if I can make a neat job of the improvements, they can be equipped with 3 wire cords, safety type caps where appropiate, and sound OK, then I will be able to find new homes for them.
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