One
of the first encounters with electronics that I remember was pulling
apart the old family wireless (radio), made in (I think) the 1940's. It
was in the temporary dwelling in 1956 when my parents first settled in
Brisbane. When the main house was made, it moved inside for a time (as
at right. That's me around Christmas 1960). It had become unreliable,
and we had another, smaller radio that dad won at a raffle, so Mum
finally agreed to its demise. It was a console model, about a metre
tall, with a large backlit dial, bakelite knobs, and a magic eye. The
loudspeaker was quite large, about 30cm, and I believe had an
electromagnetic field that doubled as a power supply choke. The valves
were mostly of the classic "ST" shape ("coke bottle"), and most had caps
(a grid or anode connection at the top of the glass envelope). At least
one had a metallic red coating; this apparently acted as a shield. I
believe that the bases of the valves were of the European "P" style
(having a series of metal studs rather than pins). I'm told that this
means it was likely a Philips set.
It's interesting how much can be learned by taking something apart, as opposed to putting something together. I suppose it's the old analysis verses synthesis thing. It could well be that my propensity for pulling things apart, which started with that wireless, that fuelled my later interest in disassembling computer programs.
I remember getting a bit of a reputation for being able to fix TV sets. In those days, it was well worth repairing electronic appliences, and indeed with the low reliability of valve equipment, it was necessary. At one stage, there were three televisions, all valve models, in various states of order. Always I seemed to get the hard cases; it never was an open circuit heater on a valve that could be found by inspection. Later I realised that the simpler cases were being fixed by "handyman" types, and only the difficult cases came to me. Electronics had an elegant simplicity then; you could actually see all the components, and put an (insulated) alligator clip on any wire to find out what was going on.
Some links to valve and radio sites:
Not very
much later, I attempted a more ambitious project. I think it was adapted
from an Electronics
Australia project. (If you know the issue, please email me). I
substituted some of the transistors for those that my Uncle could
supply (and happened to be used in hearing aids). I remember that these
were the old glass encased transistors. They had to be coated in black
paint, to prevent photons from turning into leakage current. (Later
projects expoited this sentitivity to light). This design employed
plug-in coils to change bands; I can recall buying most of the parts
from Tracksons in Brisbane (they
closed their radio parts division soon after, but we had a better
supplier by then: KitSets Australia.).
It worked quite well, although it was prone to "motorboating" and thermal runaway of the power audio transistor. I was very proud of it. When I later joined the radio club in Indooroopilly, Brisbane, I brought it along to show the other members. One of the other members also had made a radio; his had two valves. Who had the more complex radio? Although mine had three active components, his had two dual valves (i.e. there were two active components in the one glass envelope), so his was the more complex.
Regrettably, I no longer have any parts from that radio, altough the speaker above looks very similar to the one that I used. (In the early seventies, I don't think Taiwan made any high tech components!) It used an Eveready 276P 9v battery; thanks to Ian Malcolm for the image.
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| External view (from the magazine, not as I built it) (88K) |
Circuit diagram (89K)
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After the 3 transistor radio, I attempted something much more ambitious: the EA160 from Electronics Australia (December 1970 issue). This more complex radio was mains powered, had the luxury of switched band changing, and featured 16 transistors and one integrated circuit! I had a lot of trouble getting it to work (probably due to the sloppy "dress" of my high frequency wiring).
To help with aligning this radio, I got Mum to buy me this RFO for a
birthday or Christmas. It was one of the last pieces of equipment to be
manufactured with valves (vacuum tubes). As far as I know, it still
works. Made in Japan. Note the modern-looking moulded power cord, and
the "bread slicer" variable capacitor with the vernier drive. It sports
a printed circuit board, which were popular in the later years of valve
equipment (even in television sets). Note that the lower knob has been
replaced by a spare for the EA160.
Very little of that project is left today. Below is a thing called
an "SK-10 board" that was used to prototype small circuits. Note the
left chip; it bears just the generic part number "7404" (a hex inverter
TTL (Transistor Transistor Logic) chip). The one on the right is a
normal chip; it has a manufacturer's logo (in this case, the stylised NS
of National Semiconductor), a date code (indicating the year and week in
which it was manufactured), and the full part number (DM74121N). The
reason is that the chip on the left is a chip that failed full testing;
the manufacturers disposed of these as junk. Some of these worked fine
at ordinary temperatures, so there were suppliers who would stamp them
with a generic part number, give them a quick test, and sell them
cheaply. My serial computer was built almost entirely of such dodgy
chips.
The computer was never completed, because of a simple practical problem
that I was not aware of at the time: inductance in the power supply
wires to digital circuits cause unexpected glitches, and "bypass"
capacitors are needed to prevent this. Nothing that I built seemed to
work properly! By then, microprocessors were coming out, and my design
was hopelessly obsolete anyway, so I abandoned it.
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Last modified:26 Dec 02: Added Rod Smith's site,
Adelaide Valve Sales links