Replacing link cable in 1950s Blaupunkt Car radio

[Old Sparky]

The cable in question is a screened one just under 1 metre in length, which contains three individual cores, red, black, & blue, plus an inner single core screened cable for the audio siganl, the whole being terminated in a 6 pin plug to connect the head unit to the amplifier/ power supply. The outer screening is a heavy duty woven type, the problem being that the insulation on most of the inner wires has perished (as is only to be expected, I guess, since the radio is almost 60 years old!) Preumably no similar cable is manufactured today, so does anyone have any idea(s) as to with what to replace it? All I can think of is to use a single screened lead for the AF, and individual wires for the other connections, one of which carries the LT (6 or 12v) supply from the on/off switch to the amplifier, so needs to be rated at several amps., but if there is no outer screen, interference may well result. I've tried, without success, to pull out the old wires from the original cable.

[Mark Hennessy]

In the past I've used CCTV cable for this sort of thing. Have a look at this for an example:

http://www.kenable.co.uk/product_info.ph...ts_id=3361

The challenge will be finding somewhere that will sell you a small quantity. I don't have any here, unfortunately.

Alternatively, you can make your own cables to any specification using braided sleeving. For example:

http://cpc.farnell.com/1/1/184-braided-s...-ffr3.html

Of course, a bit of heat-shrink is needed at both ends to stop it fraying. Or you can fold it in on itself and tie-wrap it, or you can heat the ends to melt them together. I use this stuff a lot, and like it.

I don't expect that an overall screen is necessary, but the audio line obviously should be screened from the adjacent conductors. The braided screening on the video cable linked above does look a bit frail, but you'd have to test it - obviously the circuit impedances will dictate the amount of pick-up that you'll get.

[camallison]

Maplin do this by the metre:

http://www.maplin.co.uk/p/rg592-cctv-pro...etre-n49gg

Colin

PS - also Cricklewood do cable by the metre:

http://www.cricklewoodelectronics.com/Cr...hp?cat=313

[Old Sparky]

In the past I've used CCTV cable for this sort of thing. Have a look at this for an example:

http://www.kenable.co.uk/product_info.ph...ts_id=3361

The challenge will be finding somewhere that will sell you a small quantity. I don't have any here, unfortunately.

Alternatively, you can make your own cables to any specification using braided sleeving. For example:

http://cpc.farnell.com/1/1/184-braided-s...-ffr3.html

Of course, a bit of heat-shrink is needed at both ends to stop it fraying. Or you can fold it in on itself and tie-wrap it, or you can heat the ends to melt them together. I use this stuff a lot, and like it.

I don't expect that an overall screen is necessary, but the audio line obviously should be screened from the adjacent conductors. The braided screening on the video cable linked above does look a bit frail, but you'd have to test it - obviously the circuit impedances will dictate the amount of pick-up that you'll get.

Mark, that cable from Kenable would be ideal, but, as you say, finding someone who will sell me a couple of metres of it might be difficult. In the meantime I've put a length of braided sleeving on a CPC order (didn't know they stocked it!), and may make up a cable. The outer screen was no doubt necessary, since this is a valved car radio originally powered by a vibrator PSU mounted, with the o/p stage, in a seperate box, the screen forming the earth connection between head unit and amplifier.

[Old Sparky]

Thanks, also, for your suggestions, Colin. The cables sold by Maplin and Cricklewood may well be suitable. As the job isn't urgent, I'm keeping my options open as to which way to go about replacing the cable. The radio in question is a Frankfurt dating from about 1956, and has VHF/MW/LW coverage, which should work very well when fully repaired.
Incidentally does anyone know what sort of capacitance the spark plate in the DC supply has? The one fitted to this set was leaky, although dismanling, cleaning, and reassembling it has improved matters, it still measures ca 2 Megohms to ground on a DMM.

[Mark Hennessy]

Most of the CCTV cables available today are of the figure-of-8 "shotgun" variety, so look like over-grown bell-wire. I assumed that wouldn't be appropriate for this restoration, which is why I spent about 15 minutes chasing down the variety I used 10+ years ago - being in one overall PVC cable. Also, the "shotgun" types tend to only have 2 cores (for power), which isn't enough. The stuff I used had a red/black pair for power, plus 3 smaller cores for audio and control. If only I still had access to the drum I bought all those years back - that was in my previous job...

Regarding screening, I'm of course aware about the vibrator PSU, but what is going to be susceptible to interference radiated from the supply? Obviously, the audio signal travelling down the bundle in very close proximity. But what else? Assuming this is to be fitted to a car of similar vintage, what other sensitive electronics will be present? Given that an exact copy is not available, this is where you have to put your "engineering" hat on, and ask yourself these sorts of questions. It's why I mentioned the impedances seen by the audio cable in my first post.

If screening of the HT pair is really important, and you don't mind have multiple cables inside braided sleeving, then things get a lot more interesting. There are a lot of cables that we use at work to carry balanced audio and control signals, and can be of quite decent current-carrying capability. For example, FST:

http://www.canford.co.uk/Products/31-001...pair-Black

This stuff is probably a bit thin (7/0.2), but what is the HT current? But a couple of runs of this (one for power, one for audio), plus one or two standard single cores for other functions could easily fit into braided sleeving of the right diameter.

It's worth spending a bit of time on the Canford site, as they have a massive range of cables, and they sell per metre...

[pwdrive]

This lot do screen braiding in shorter lengths ie: not a full reel, they do a 1 meter length but that's about 7/8ths diameter, you might be able to pull it to reduce the diameter.

http://www.hypex.co.uk/home.php?cat=366

Lawrence.

[Mark Hennessy]

That stuff looks pretty good Lawrence. I've sure the diameter is variable to a reasonable extent, though perhaps not as much as the plastic stuff.

The plastic stuff could be fitted over the metal stuff if required. Basically, roll your own cables to any specification

Another thought: a Scart cable might do the job. If you could find one that has individually screen audio/video cables, but wasn't of the "fully-wired" type (with RGB), that would probably do the job. It would contain a pair of screened video cables, four screened audio cables, and a few individual cables. More than you need, but you could use the screens of these to provide increased current capability if needed. There will be an overall foil screen, and the diameter should work out to be 6-8mm from memory...

[pwdrive]

The power feed cable for the Eddystone 358 is also braided but those things are quite rare.

Lawrence.

[Old Sparky]

I've made up a new cable using lengths of multi-strand wire for the supply, earth and switching leads, plus a screened cable for the AF. Will bench test the radio maybe one day next week. As to what vehicle it will be fitted in, I don't know.
It's a radio i obtained some years ago, and, if the repair is succesful, I may offer it for sale.