(Possibly OT) Positive or Negative earth?

[George]

Can I have some of what your're on?

[Dave Plowman (News)]

Not so - the reminance only allows generation of one polarity. To change the polarity you have to pass the wanted polarity through the field windings. Usual way is to wipe a live wire across the field terminal.

[Dave Plowman (News)]

Of course you could fit a valve radio - these aren't polarity sensitive.

Other thing with speakers is finding one of the correct size these days to fit the mounting - although I don't think the Minor had one.

[Dave Plowman (News)]

IIRC, all cars started out negative earth. IIRC again the change to positive earth was said to improve points and plug life. But of course many makers never did change. Silicon semiconductors made the change back to negative earth desirable.

[Dave Plowman (News)]

That's one way to make sure the aerial performs poorly. The trimmer found on most older sets for AM reception won't work with no screen. A better way is to insulate the aerial mounting. But better still to change the car's polarity. It's a simple enough matter.

[Andrew Gabriel]

My parents had one of those. I think it was originally in an Armstrong Sidley, but I first recall it in the Vauxhall Victor my father transplanted it to. Had a dashboard part the size of today's car radios, linked with a thick multiway cable to a large metal box in the passenger footwell which had the bulk of the circuitry in it. Probably about 8 valves (2 in the dash part). There was a vibrator in it to generate AC to transform up to ~300V. This was in a plug-in can as it wore out and needed replacing from time to time. Of course, they were no longer available, so I kept it going until it really had no contacts left at all. When it was on its way out, you had to kick the radio to get the vibrator going! Eventually I built a transistor osciallator to replace it. When the Vauxhall Victor went to the scrap yard, I rescued the radio and used it in my bedroom for a while, but I've no idea where it is now; I suspect it was thrown out at some stage. It drew the best part of 10A which made it rather difficult to power at the time, outside of a car.

[Trevor Smith]

Also feel if the heater fan is blowing or sucking, that is if the wires were changed round when the polarity was changed. Trevor Smith

[meow2222]

Which part of running a neg earth radio on a pos earth car do you think is so difficult?

NT

[George]

The one were it says...hello, puff of white smoke.

[The Natural Philosopher]

and thus invented planned obsolescence? :-)

[Graeme]

In message , "Dave Plowman (News)" writes

I didn't realise that - thanks. My Dad's Wolseley 1500 had a valve radio, which was fine, but took a couple of miles to warm up.

Indeed. I found a suitable speaker, complete with plastic housing, at a boot sale. Will probably mount it below the front parcel shelf.

[Dave Plowman (News)]

[snip]

Radiomobile made an all in one valve radio - a masterpiece of packaging, considering it included push button tuning which was a mechanical system moving inductors.

In the early '60s I found a Bluespot valve FM radio in a breaker's yard and fitted it to my MG. Had to convert it from 6 volts. That was a two piece one - I doubt you could have packaged that into a standard case.

[The Natural Philosopher]

Well they ARE polarity sensitive, but they need a high voltage inverter to get the HT and many of those were NOT polarity sensitive.

[Dave Plowman (News)]

Talk about nit picking. Many electronic devices are polarity sensitive within the appliance - you often get a mixture of PNP and NPN transistors for example. Even within the same chip. But what matters to 'us' is the external polarity.

Oh - if you really want to nitpick, modern electronic inverters are available to replace the original vibrator for some makes - and these

*are* polarity sensitive...

[The Natural Philosopher]

Arr, Yewl never beat a proper vibrator..these New fangled electronics don't give my missus the same buzz at all.

[George]

transistors

Damn! your missus is behind the times...they have hands free ones now,bit like a wankel engine but with the thing on a rod. ;-)

[Bob Eager]