Those were the days is a lovely song by Mary Hopkin. She also happens to be the singer I liked best. I always regret of not buying all her CDs while they were still available in the music shops a few years ago. Once its gone, its gone. Anyway, once upon a time....in the '60......in a place known as the Pearl of Orient - Hong Kong......
Magnetic personality
It was five years into my primary education when I was taught by a science teacher who
knew a lot on electricity. In those days, just owing a simple powerful magnet can be real fun.
Once he told the class how he can build a simple electromagnet, using a large iron nail, about 50 turns of enamel copper wire and a 1.5V cell. I asked him for all the details, built myself a simple electromagnet and was happily
playing around. With two cells in series, the magnetic attraction was
stronger but its strength was far far weaker than a magnet I salvaged from a loudspeaker. There must be a way
to create a stronger magnet.
Real Power
I have correctly figured out the reason being the dry cell. The magnet gets stronger if more cells were used. Then
naturally, the AC power socket on the wall, came to mind. It was those black 15A round-pin power socket without any safety shutter of any sort. The socket had three uncovered
round holes where I can see the internal shinny copper connector from outside. I knew power was a nasty thing and should not be touched
by bare hand but the thought of a powerful electromagnet was hard to resist. So with an
insulating pliers, I held the nail with the two coil ends on one end separated at the same distance equal to the holes of the socket. Then I pushed the coil ends into the socket. A
loud bang and flash resulted and the main fuse of the house was blown. Copper on both the
socket connectors and the coil ends had vaporised. My father had to pay for an electrician
to replace both the fuse and the socket. The electrician said I was lucky but did not
bother to explain why. Why he said that remain unanswered for years to come.
Faulty resistors
During the first year of my secondary education, I met several classmates who shared the same
interest in electronics, or rather valve projects. Instantly, they became my best friends
and we shared all information we knew about electronics. The only learning resource we can obtain was a
locally published chinese monthly magazine on electronic projects which probably contain
translated articles from the Wireless World Magazine. New and genuine electronic parts
were far too expensive for most students to afford so we turned to old surplus items
obtained from a well know street in Hong Kong - the Ap Liu Street. Most often the surplus
store owners had absolutely no idea what those surplus parts were for and sold them according to
weight. One such owner was willing to cut down the price on a box of mixed value resistors
after I told him I knew these resistors were faulty and I only wanted their leads as jumper wire. To convince him I then showed him without fail that all of them conduct electricity in both directions using the x1Kohm range of a multimeter. Little did I realised my trouble had just begun. Every time I needed a resistor, I had to search through several thousand resistors before I convince myself that I "certainly" did not have that resistance value and need to buy it from the component shop.
Once popped
All our valve projects require DC high voltages and so surplus old transformers and electrolytic
capacitors were our favourest. Many transformers ends up smoking but the worst had to be a
blown up high voltage electrolytic capacitor. The loud bang and the bad smell of the burnt electrolyte and all the bits of brown paper spread everywhere reminded me of the incident for a long long time.
Silence is golden
There was a time when I and all of my friends decided to build a 5 Watt single valve audio amplifier
using the 7189A tube. We each bought a new 7189A tube which costed me about
a month's pocket money. My friends got theirs amplifier working soon but I had no luck. The amplifier remained
silent. I checked and the high voltage is there, the tube filament lit but the amplifier made no sound. The valve
plate then gradually grew dull red which indicated something was wrong with the circuit. I
dare not risk to shorten the life of a new tube by letting it grew red for longer than
necessary. I turned off the power, check and re-check but could not find anything wrong with the wirings. I
then dismantled all the components and wirings, and rechecked all components using a VOM.
I even drew up a wiring diagram and started again from scratch. To my disappointment, the
amplifier still would not work. I was frustrated. I invited my friends home to examine my
amplifier but all their checking confirmed the correctness of the wirings. They gave up, me
too, though very reluctantly.
The sound of music
A week later, an article appeared on the electronic magazine explaining the construction of a
pentode. Out of curiosity, I took out the new 7189A and looked very carefully at its
internal connections from the pins to the gate and plate. There I noticed a small gap
between the pin and the connection to the gate. The thin connector, which was supposed to be
spot welded to the pin, had come loose with a less than 1/32" (sorry, no metric measure yet)
gap, probably due to bad workmanship. My amplify signal stopped at the bloody pin! without
reaching the gate. Only one of my friends was willing to lend me his 7189A for a swap
test, though he insisted it should be as quick as possible after the filament is lit, in
fear of my circuit damaging his tube. Sure enough the amplifier worked immediately.
Unfortunately, I could not return the defective valve as component shops in the '60s
always got away with the clause "Goods sold are not returnable" on the receipt.
Instead I got a new 7189A and dug deeper into the theory of valve operation. The red-hot
plate was a good pointer if only I knew the meaning behind it then.
Radio silence
After the amplifier project we turned our interest towards making radio receivers. We saw
many simple circuits involving an antenna, a coil with a variable capacitor and a crystal
earpiece. We were wondering why there was no volume control on all these circuits. The
most interesting component of all was what was known as a stone or crystal of some sort
and a fine metal needle poking at it. We searched high and low for the sacred stone but no one
locally seems to carry them or know what they actually were. Until at last another circuit indicated the
use of an 1N34A 'diode' in place of the stone. Luckily the component store did carry the
1N34A and so we all built a set, with 5 feet of antenna wire hanging out the window of our
apartment block. Unfortunately, nobody had received a single station, not even noise. I only find out
years later that for that circuit to work, one has to have high Q coil and a wire antenna
of at least 30-100 feet. It also answer the question why there were no volume control needed.
Transistor operation
By then the germanium transistors started appearing and opened up many project
opportunities. Among those were the popular 2SB75 & 2SB77, and the expensive 2SB426. I
often wondered what kinds of transistors are 2SB01, 02... and so on and why there are so
many type numbers. Luckily, nearly 90% of the projects used the above three transistors or
worked faultlessly using them as substitution. Very soon we discovered that by
cutting open the metal can of the 2SB75 transistor, it can be used to sense light and has
a much faster response than a CDS(known today as LDR).
Baked 'beans'
We could tell the valves era had come to an end and it was all transistors from then on. Very
quickly there came the silicon transistors and soon lots of unmarked transistors
appeared in the surplus market. These transistors were made with a dark brown epoxy base
with a shinny black dome shaped epoxy head. The legs were golden color. Everybody was calling them "black
bean" and qualify them with 'large' or 'small' according to their size. I suspected
they all came from a company named 'FairChild' as sometimes I could see a letter F on the
epoxy. Needless to say, these unmarked transistors had a mind of their own and it was pot luck to
use them in circuits. Some got very hot and died and others went silently without a trace.
However, they only costed one-tenth that of a genuine part.
What's inside that count
I still remembered that someone were using those unmarked transistors to build AM transmitters and sold
them in the ApLiu Street. The
selling prices were according to how many of these transistors were used, just like the
price of all the transistor radios sold in the shops then. I could not afford to buy the one with
7-transistors but did saved up enough money for a 4-transistors transmitter. The man opened the case of one
such transmitter, pointed to me the four transistors and some coils and then happily took my money. Wasting no time
back home the circuit board fixing screws were off revealing the underside of the transmitter. It was no doubt that 4
transistors were on the board, alas the leads of 3 transistors were all soldered to the
ground plane. My first reaction was how this "special configuration" can actually work to
increase the power output of the transmitter. A display of stupidity at its very best.
Heavenly scented
Next came the light emitting diode (LED) and the TTL ICs. It was kind of cool to have a
red LED watch with blank display. Press and read the time, right? Electronic projects
involved printed circuit board became common place and the board were easy to make using paint based
permanent marker pens. The traces produced using these marker pens were incredibly
resistant to pcb etchant. I often drew the traces on the board and left it to etch
overnight. Nowadays,the traces are easily attacked by etchant and must be
kept at close watch during pcb etching process. The chemical formula in the paint of these pens must have changed, presumably as someone decided to sniff them. How I hated you, pen sniffers.
The COSt of SIN
Electronic calculators the size of a thick book made their way into the market but they
were limited to very basic arithmetic functions. One day it came as a great new as someone in the
class spotted a shop selling a calculator which calculates the 'Trig' functions and we all
shorten our lunchbreak to have a look. Yes, keys were marked with 'SIN' and 'COS' but it
cost nearly the price of a car. I knew the days of my "Aristo" sliderule was
numbered. With more transistors integration and large scale integration, fewer and fewer
ICs were needed to build a product. At last I had my own calculator, the one that
operates on Reversed Polish Notation(RPN). The operation was awkward at first but after
one got the feel, it was more than natural to use. RPN makes lots of sense, especially
with its similarity with computer languages. I can explain RPN to you quite simply. In calculation,
ask yourself whether you can use the immediate
value, if yes go ahead else dump it on the stack for later use. I don't know why there are
so few demand for such calculator. I still use one regularly.
Personal computer
I was introduced to the computer in college where computer meant several rows of printing terminals where we
all typed and got the result printed out. Or its something that accept a pile of punch cards and printed
out something in return.
Then it came as big news that hobbyists could actually buy some IC chips and build a
computer at home. The ones I remembered were the 8080, 6800, 6502 and the famous Z80. As I
had no knowledge whatsoever of microprocessor chips, there were a lot of readings to learn
just the basics. By the time I felt confident to actually build projects using these chips,
personal computers started appearing in the market. They were very expensive by today's
standard. Some people choose the TRS-80. I and my friend had chosen a Japanese made model
PC-8001 by NEC while most others settled for the APPLE II, or more correctly the imitation
apple built using 6502. The core of the PC8001 uses a Z80, it was very convenience to
experiment with assembly language apart from the normal Microsoft BASIC operating system.
Very soon I learned to write programs which use BASIC as the main structure and calling
assembly subroutines as required when I wanted to do hardware I/Os.
The typing game
NEC, which sold the PC8001 PC, decided to kept their circuit diagram a secret so very few
hobbyists can actually experiment or built projects with it. Nevertheless, I had built my
first UVEPROM programmer after my friend successfully built his. The main program interface
uses BASIC while the actual I/Os was in assembly language. This proved to be an
invaluable tool as we could then change/patch any firmwares from ROMs into EPROMs and modified
them to our heart delight. Changing or 'improving' commands behaviour or creating new
commands became possible. We even manage to place an assembler and a dis-assembler in the
free unmapped ROM address space. Software available for PC8001 were mostly for the
corporate but armed with a BASIC machine I have had no problem developing any programs I
would like it to do. Game softwares hex codes for the PC8001 were available(printed) in some japanese
computer magazines but one has to manually type in the hex code using the keyboard. Just
imaging typing in 20K of meaningless hex codes one by one. Mistakes were inevitable.
Luckily, I can ran a checksum program later to find out where the typos were. It usually
took many days to type in such a program and then finally ran it. Most of the time one had to
guess what the japanese characters on the screen meant in order to run the game. It was
fun to have 'Space Invader' running at home while others were paying just to play them in
the street arcade game consoles.
(To be continue)