Charging a car battery

[Terry Casey]

You are quite right about it most definitely NOT being 75 ohm cable, Dave - the most important thing about it was that it was very low capacity. We managed to get a reel of it from PYE's spares/component wing, the only place we could find it, as we lat lots of requests from customers for it - I think there was an outbreak of 'must have the aerial on thre back, for some reason, so we were always being asked for extension leads.

Rather than a spiral, the very fine centre conductor was formed into a zig-zag with a long zig and a short zag - I hope you get my meaning! - which ran inside a fairly rigid clear plastic tube with the screening surrounding that. The zig-zag kept the wire as close to the centre of the tube for as much of its length as possible to maintain the low capacity.

The cable supplied with the aerial formed part of the input tuned circuit, with the low value trimmer being used to balance the exact capacity of the cable. Exceeding the length of the cable increased the total capacitance so that it was outside the range of adjustment, so this had to be addressed.

Fortunately we knew the capacitance of the cable per metre, so we could easily work out what the total capacitance of the entire run would be and calculate the value of a series capacitor so that the radio would see the correct figure.

Egen made some very nice plugs and line sockets with similar caps and cable clamps to a normal coax plug, so we were able to solder a sufflex capacitor of the right value onto the end of the centre conductor and clamp the plug in the normal way.

The sufflex capacitor sat neatly inside the body of the plug with its other wire potruding from the centre pin so all we had to do to complete the job was to solder and trim this wire.

[Terry Casey]

The original data on the 5-10 as published by Mullard is here:

It says that: A CR network (C1, R1) [C13 and R22 in your version of the circuit] shunting the anode load produces an advance in phase which increases the stability of the amplifier at high frequencies.

The phase splitter, bt the way is an ECC83 - not an 82.

I must have built around a dozen of these back in the day.

Excellent performers!

However, Bob only mentioned one EL84, so perhaps he was thinking of the Mullard 3-3:

Outperforms anything else of a similar nature!

[Terry Casey]

It would have been an Ever Ready B126 or equivalent, I would guess.

Layer cells, as in a PP£ but much bigger. Rectangular, in two stacks of 30.

Overall size: 3.75"x1.75"x2.5" (or 95mm x 45mm x 62mm)

Assuming parallel connected filaments - not heaters - a single UR could have been used but commercial receivers used an AD35

- containing two much larger cells in parallel to give a longer life.

Overall size: 3.125"x2.625"x1.5" (or 80mm x 67mm x 38mm)

[Terry Casey]

I've just spent quite some time trying to find some information on it but with no joy.

The set was a slim line 17" set and I'm sure it was 405-line only.

The transistor wasn't a mod - it was designed that way from new but, as we'd stopped selling PYE a few years earlier, I never saw one working.

[Bob Eager]

As I said, I did have a preamp, and I think there was an ECC82 there (one half for each channel). And probably an EF86 before it.

[Bob Eager]

90V battery, certainly.

In my case it wasn't (see below). Combined in one 'box' wwere the 90V and

1.5V.

I was lucky. I had (via a Royal Marine barracks and the signals department) an almost unlimited supply of those combined batteries ...

The one I mention above was in fact a TRF. I did later build a superhet (and wound my own IF transformers, with Litz wire - horrible stuff). It worked OK, but not brilliantly.

[The Other John]

During the war my mum and I lived in Hampshire with an aunt and my cousins and she had a 'wireless' which needed an HT battery, a grid bias battery and an accumulator for the filaments. The latter had to be taken to the local bike shop to be recharged and IIRC they actually exchanged the discharged one for a freshly charged one.

[tabbypurr]

reduce gain at high frequency

NT

[tabbypurr]

they were the main type offered to the public in the 19 teens, 20s & early 30s. They also hung on at the cheap end of the market in the 40s.

NT

[tabbypurr]

the cap sections needed to not quite track because they were in different bits of circuit with differing chracteristics. That's where the problem was. Later that was all figured out & the extra bits became affordable.

NT

[Johnny B Good]

It would have a characteristic impedance, presumably a lot higher than the more typical 50/75/93 ohm impedance figures typical of proper co-ax feeder cable. I'm not sure whether it could have been as high as 300 ohms which would be a side effect of trying to keep the shunt capacitance per metre figure as low as possible since it was being used not as a conventional co-axial feeder working into a matched load but simply as a screened section of the antenna designed to eliminate electrical noise within the interior of the vehicle from interfering with the radio signal picked up by the external portion of the antenna mounted outside of the Faraday shielding of the vehicle cab.

The early MW/LW car radios used valves which, when used in common cathode mode, provided a high impedance input which could be connected across the first stage tuning circuit for maximum sensitivity without compromising the Q of the tuned circuit.

It was standard practice to use permeability tuning (variable inductance) in order to keep the L:C ratio as high as possible to get the maximum voltage magnifying effect out of a circuit where most of the capacitance was supplied by that of the *shielded* antenna wire and the short external unshielded bit that acted as an electric field probe antenna. The combination of variable inductor/adjustable padding capacitor/screened aerial wire section plus exposed aerial rod capacitance, formed the first tuned section of the receiver.

There were two very good reasons to choose permeability tuning over variable capacitor tuning, both touched upon above. Firstly, and foremost, the need to eliminate the "pot down" effect of a tuning capacitor and secondly, the elimination of a bulky two/three gang 300 to

500pF air spaced tuning capacitor in favour of the much more compact slug tuned two/three variable inductor bank.

In theory, it shouldn't make any difference as to which part of the tuning dial you found a suitably weak signal by which to trim the aerial circuit to peak response provided the Local Oscillator (LO) tracking had been closely matched to the RF tuned circuit(s). However, choosing a suitable station at the HF end of the band may have helped compensate for LO tuning tracking errors in most cost effectively manufactured designs.

Although such a small 'probe antenna' setup only brings in a tiny fraction of the signal that a full 100 odd foot vertical quarter wave ground plane would, the effective broadcasting range on the MW and LW wavebands is limited by the very high noise levels from atmospheric sources (QRN) in those wavebands. This circumstance meant that such tuned probe antennas were entirely fit for their intended purpose in spite of this obvious shortcoming.

[Johnny B Good]

I had a look at the description in the linked page and they do seem to be 'just the ticket'. The only concern I had was the absence of any mention as to what the 'maintenance' voltage was. If it's 13.5v, ok but if it's 13.8v I'd be inclined to plug it in via a cheep 'n' cheerful electromechanical timer set to let it run for an hour or two per day rather than chance leaving it permanently floated at 13.8v month after month.

[Bill Wright]

I've checked a lot of batteries. I regard 11.75V as fully discharged.

Bill

[Archibald Tarquin Blenkinsopp]

I have little doubt that your memory is better than mine regarding the model, but I would never have associated transistors with single standard VHF sets.

Was flywheel sync in use in VHF sets?

I could look it up, but my Newnes Radio and TV servicing library went in the bin a number of years back.

Amazing times though, it was interesting to see different manufacturers approaches to electronics problems.

Thorns "wattless dropper" was one of the most memorable, particlarly when the "dropper" shorted.

I have recollections of cleaning terret tuners, in particular during the three day week when during power cuts we were issued portable gas lamps to do repairs by [We were salaried].

Thanks to the miners our customers had VHF tuners that were absolutely spot on, no hairbrush or comb wedged between case and tuner knob for them. Pity they were all on UHF and couldn't appreciate it. :-(

Happy days

AB

[Dave Plowman (News)]

Same here. Can't resist a treat when doing the 'normal' shopping. But everything does get used - eventually.

[Dave Plowman (News)]

Ah. I have a very accurate digital voltmeter sitting across the car battery, and it has started with a lower voltage than that.

(The voltmeter is wired directly to the battery, via a relay switched with the ignition.)

[The Natural Philosopher]

With a decent transformer, probbaly better quality thanm most amps of that power around today:-)

[The Natural Philosopher]

Yup.

Boosting gain just boosted the noise as well.

[Ian Jackson]

In message , "Dave Plowman (News)" writes

One dark night at the beginning of January 1965, when in my 1953 Ford Prefect, with a dead flat* 6V battery (almost zero volts), I rolled it down a hill from Englefield Green to Runnymede (A328) - and bump started it. At the bottom of the hill, when I switched the lights on, the additional load on the dynamo nearly stalled the engine. Of course, those were the days before alternators and clever electronics.

*It was dead flat because I had my amateur radio equipment installed in the car - and I had foolishly left the valve heaters on all over the Christmas holiday week. Fortunately, I had a spare car battery.

[charles]

Good thing you had control before you hit the river ;-)