Car battery polarity

Or you turned it into negative earth without knowing :-)(

You can still get one

A good write up on the history

My radio wouldn't have worked if I had.

No - different.

Sacrificial anodes are blocks of zinc which are replaceable. On a ship they are normally placed aft near the propeller(s) for technical reasons.

Perhaps you are correct re the attached bit, it was 50 years ago give or take 😀

Even rear window heaters / demisters were a novelty. I recall one which was a long, chrome, tube ( I assume with a heating element inside) which was fixed to the rear parcel shelf. ( Hatch backs were all but unknown, the A40 Farina was around but not common. I remember a friend of my father having one.)

That will be why the markers on the recently installed oil pipeline where I walk the dogs warns of a voltage, I cannot remember the exact wording. The gas pipeline nearby has concrete markers with covers and where the covers are broken you can see two brass terminals, for monitoring I suppose?

Don't be daft.

unless they were

as I did with my '64 Anglia. Mind you, the power take off pulley on the engine wouldn't stand the extra load. I had to buy a FordSport cast one,

Well by convention PNP transistors did indeed conventionally use a positive earth, They didn't *need\* to, but it simplified the circuitry which was basically copied from valves, but the PNP transistors were reverse polarity to valves, hence the positive earth.

Just for the record, almost all the early transistors were PNP. Some of the car radios were hybrid, using 12V low-voltage valves for all but the transistor audio output stage. The radios with switchable supply voltage polarity (where all the internal 'works' were floating) appeared (by necessity) during the change from positive to negative earth.

I am surprised. Most of the issues with transistor amplifiers then were in achieving reliable power.

Germanium PNP power transistors were very expensive. And pretty crap

My recollecion is of amplifiers with (nechanical) inverters in to step up to a few hundred volts

There certainly were mixed technology car radios, I got an old one from somewhere and fitted it in my 1966 Spitfire.

Really early car radios were all valve and had a box under the bonnet and a dashboard control, HT was generated from an mechanical device with an induction coil and vibrating contacts.

This one I had was all one box that fitted into the dashboard and had two valves (B9A base as I remember) for the RF stages and transistors for the AF. The valves used 12V HT (a quick Google suggests ECH83 and EBF83). From the era, probably Ge transistors in the AF?

My mother had a very early GEC portable radio looking just like the later 1.4V B7G valve sets but with a PCB and transistors and a lot of empty space; that was all Ge with type numbers GETxxx.

nib

Yes - this is exactly how things evolved. Valves could be persuaded (or designed) to work at surprisingly low HT voltages, but you couldn't get much power out of them - hence the use of AF power transistors to get enough audio. This was often just single-ended Class A stage, and therefore drew quite a high quiescent current.

In 1968 I built a 12v power amplifier with a 10 volt output swing, using IBM stock and 2 OC22 output transistors. All in Germanium

Wow. Never ever heaqrd of those. Hearing aid valves on 22,5V yes...

That is early. Mostly we were on to OCXXX style transistors by the 60s - Audio OC 71 and 72 and OC81 for power output using transformers OC170 for RF and IIRC OC45 for IF use.

Then AF and AC bumbers, then B numbers for silicon NPN and complementary N-P in the 70s

There were "space charge" valves developed specifically for 12V HTs

You may find this interesting

In all cases you needed an output transformer. Whilst its true that an OC35 could kick out about 5W in a class A, a pair of OC82s could do very similar in push pull class B.

And a quad - dual pairs - even more.

Ta for that!

One thing I remember from playing with valves years ago is that if you connect a sensitive ammeter between cathode and anode then, provided the cathode is hot, a current will flow. So it's possible for electrons to boil off the cathode and travel to the anode with effectively zero volts on the anode.

nib

A negative voltage will build up at the anode, due to the electrons landing there, which will drive the electrons off the anode and through through the ammeter back to the cathode. Ultimately this is driven by the thermal energy of the cathode electrons. Interesting, though.