Help Identifying a Car Radio

[Murphy Maniac]

Can anyone help to identify the car radio shown in the photos please?
The only identifying mark on it is the Ford logo on the tuning scale.
It is from a Ford Classic and I want to convert it to negative earth operation. A circuit diagram would be really helpful.
Thanks.

[ronbryan]

Can you post a photo of the set with the cover removed, as a view of the internals may help with identification.

Many low cost radios like this were made for car companies by Plessey. This one I assume just provides one preset LW station, selected by rotating the tuning cursor to the extreme right. Not all car radios in the early sixties had battery polarity reversal facilities built in. Philips produced a DC-DC converter (22-EN-9726) which allowed positive earth radios to run with negative earth batteries.

Ron

[TonyDuell]

Although not useful here, the 'opposite' converter, +ve earth input and -ve earth output was common-ish in the late 1970s/early 1980s. At the time many car radios, radio-cassettes, etc were for -ve earth supplies only, the converter allowed them to be used in older cars. Said converter would also turn a -ve earth 12V supply into a -ve earth 24V supply (consder taking the -ve input wire as the reference point, you effectively ended up with the converter output on top of the 12V input) and in many cases they'd run at a 6V input, thus also changing a 6V -ve earth supply into a 12V -ve earth one.

The converter I saw was quite simple inside, a couple of power transistors, a ferrite core transformer and passives. It's the sort of thing you could probably make using an SMPSU control ic nowadays once you'd designed the transformer.

The other trick is to isolate the car radio chassis from the car chassis. Connect the supply lead of the radio (which is the -ve side of the radio supply of course) to the car body , and the car supply lead (+ve) to the radio chassis. Then isolate the aerial connection with, say, 100nf in series with both the screen and centre conductor to prevent a DC short circuit (battery positive to radio chassis to aerial screen to car body to battery -ve). If you try this, make sure you have a fuse in series with the +ve wire to the car radio chassis just in case anything shorts, and take great care. A car battery can supply a very high current if shorted.

[Radio Wrangler]

Some Ford branded radios were made by Plessey, but some were also made by Ford themselves. I remember they ordered a bunch of sig gens from HP and I asked what they were for. But that dates it as after the period of this set.

David

[ronbryan]

Here is a photo of a sketch of the Philips 22EN9726 polarity converter circuit I traced out a very long time ago. All done with a single power transistor and mounted in a round metal can as far as I remember.

Ron

[Murphy Maniac]

As requested, I enclose some photos of inside the set. The valve line-up is: ECH81, EBF89 and ECL82.
Hope this helps with the identification.

[Cobaltblue]

I has a non synchronous vibrator so it might not actually be polarity sensitive.

One has appeared before under the name Cellgrave, which is now thought to be the maker of the tuning scale.

https://vintage-radio.net/forum/showthread.php?t=96307

And there is the set looking remarkably similar in RM

https://www.radiomuseum.org/r/vauxha...car_radio.html

Cheers

Mike T

[ms660]

Looks similar to this one:

https://www.vintage-radio.net/forum/...ad.php?t=58884

Lawrence.

[Cobaltblue]

Thanks to Lawrence's link it seems there are electrolytic caps on the battery side meaning it is polarity sensitive without modification.

However the circuit linked looks a likely candidate.

https://www.service-data.com/product.php/2245/2958

Cheers

Mike T

[radiomobile]

The non-synchronous vibrator does indeed make the set suitable for pos or neg earth EXCEPT for the input filter capacitor 25uf 25v ( red black yellow electrolytic located on vibrator base )which should be renewed anyway. If a reversible electrolytic is used (the value is not critical, any value from 25uf upwards) the set can then be used on either polarity unless of course an electronic vibrator is fitted.
The .033uf 300v ac wax tubular fitted across rectifier ac input should also be renewed. Most important as it is a highly stressed component. You will probably not find .033uf so .022uf and .01uf in parallel will suffice. 1000v minimum polypropylene types are recommended. The selenium contact cooled rectifiers are usually ok surprisingly.

[ms660]

In the OP's photos the 82 Ohm (heater circuit) and the 47 and 680 Ohm (-ve feedback circuit) tally up with the schematic and the 270 Ohm, 2.2k, 10k, 47k and the 470k also tally up with the schematic.

Lawrence.

[Murphy Maniac]

That's brilliant, thank you very much for all your trouble on my behalf. I can get to work on it now.
Very Best Wishes,
Geoff.