Those Were the Days

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. This street is about three minute's walk from the now internationally famous Golden Computer Shopping Arcade in the ShumSuiPo area. 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. On the plus side, this "training" enabled me to tell the value of a resistor by just a brief look at it.

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 blown up high voltage electrolytic capacitors. 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 checkings 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 inside the vacuum tube 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 and what to do if the sound was too loud. 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 high power 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 a 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 will be 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 ceramic base with a shinny black dome shaped epoxy head. The legs were gold plated. 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. I had none the faintest idea of what is thermal dissipation. 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 some guys were using those unmarked transistors to build AM transmitters and sold them in the ApLiu Street. The selling prices depended on 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 and counted 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 without the slightest problem. Nowadays,the traces from these marker pens 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 for pleasure. 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 news 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 costed 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 using Reversed Polish Notation(RPN). The operation was awkward at first but after one got the feel of it, 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 a calculation, ask yourself whether you can use the immediate result, 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 now. 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 had to book in advance. You typed on the keyboard and the printer printed out the result. 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)