Thursday, June 20, 2024

Caught in the waves!

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When and how a hobbyist will be carried away by an obsession is difficult to say. This time they were Radio Waves! Yes, Radio waves. Also, the waves were to be ‘caught’ in fifty years old Vintage Valve Radio that was lying in the attic, unattended and inoperative, for the past thirty years, luckily not declared scrap.

Radio stations or Transmitters transmit the Radio waves in the atmosphere and Radios or Receivers, at the other end, receive them wirelessly. Such an uncountable number of unseen Radio waves of different frequencies throng in the atmosphere day and night. Not just Radios but mobile phones, television sets, military/police wireless communications sets, walkie-talkie sets, radio remote controls, radars, etc work on the same principle.

The pandemic and the subsequent lockdown that had followed it, paralysed life. Roads were deserted, markets were closed, people were confined in their houses. The term ‘how to steal time’ was replaced with ‘how to kill time’. Exactly at this juncture, the Vintage Valve Radio caught my attention. I was determined to bring it back to life and here began the tug o’ war between a chain of untold challenges and unflagging willpower to overcome them. The latter had a winning edge and hence this article.

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I have been pursuing Electronics as my hobby since I was a schoolgoer. However, never did I read Valve technology that was already on the verge of becoming obsolete. So the first thing in my endeavour was to study Valve technology on the internet. Mr.Uday Kalburgi from Bengaluru guided me in my endeavour. As I flipped through various informative website pages on Valve technology, I wondered about the Herculean efforts the Scientists in those days must have made to open this new horizon of the Science to future generations. Those were the days of World Wars. On the one hand, there was annihilation with tremendous loss of life and property, while on the other hand Science was progressing with leaps and bounds, spear-headed by unbound creative ideas!

In the earlier days, the use of Valve Radios was restricted to the wireless transmission of News Bulletins. Later on, entertainment was introduced and the popularity of Radio grew manifold. Radios became so popular that not did they just get a special corner in the home, but also in everyone’s heart. Leisure, a cup of tea and an entertaining program on Radio must have been a great combo for relaxation! The Radio cabinets were made of quality teak wood, exquisitely carved in various shapes and were brightly polished. The Radios adorned the places as they were masterpieces of finest carpentry too. As the cabinets were made of thick teak wood and were roomy, they produced a top-class quality sound pleasing to the ear. The popularity of Valve Radios, however, declined soon. The solid-state Transistor Radios that were sleek, lightweight, battery-operated and portable replaced them. Unfortunately, the Valve Radios found their place in the scrap market.

Finally, the dusty Vintage Valve Radio was on the table now at the mercy of a hobbyist who was determined to enliven it. I opened its back panel. Cobwebs and layers of dust had covered the glass Valves, other components and a host of wires uniformly making them appear dull gray. I carefully blew air over the entire layout. Six glass valves were mounted on hard plastic bases. Every Valve has a fixed position on the chassis. Changing their position by mistake can end the game. Using a wet cloth, I carefully cleaned each dusty wire and lo! a multicoloured jungle of wires was exposed. Various components on cleaning revealed their alphanumeric codes and names of the companies. The power cord was nibbled, few connections were open, the delicate voice coil of the speaker was detached, the rotary potentiometers were rusted, the dial cord was dangling, few resistances had turned blackish, electrolytic filter capacitors were bulgy, piano-type band switch was stuck, the metallic gang capacitor was squeaky. All the paper capacitors needed replacement with polyester ones. One by one, each issue was resolved.

A more challenging task was ahead. Normally the components are mounted and connected on the chassis by referring to the schematics. In reverse engineering, I had to draw the schematic of the Radio by checking individual connections! This cumbersome task of drawing the schematic took almost a month. I knew my limitations well, hence restricted my ambition just to ‘catch’ the Radio waves and listen to any Radio station on any of the bands.

Least did I imagine that the biggest challenge was waiting for me with a wide grin. The primary winding of the Mains Isolation Transformer was open. The only option was disassembling the transformer to fix the fault. Suddenly everything came to a grinding halt.

Fixing the faulty transformer was not as easy as said. The nut bolts of half a century old transformer would not budge, let alone the ‘E’ and ‘I’ plates inside the bobbin. I was lucky that none of the windings was burnt. So after taking out all the plates from the bobbin, I very carefully started unwinding thousand and more adhered turns of the closely wound coil, trying hard not to snap them accidentally. Despite due care, the coil not did just snap at a few places, but was entangled in such messy stuff that it became extremely difficult for me to find their ends! After fixing the fault, began the neck-breaking task of closely rewinding the coil over the homemade bobbin and reinserting the plates,  one by one, in alternately reverse direction. Unnoticed, one of the turns of primary winding set loose and came over the brim of the bobbin. One small hit and it snapped the coil. In a fraction of a second, I was back to square one! The complete process of disassembling and reassembling was carried out again. I powered the reassembled transformer to carry out its off-load trial and checked the voltages of both the secondaries. I was stunned when I noticed that both the secondaries were showing raised voltages and the transformer became hot during the trial. As a quick fix, I connected a filament bulb in series with the primary of the transformer. I knew this was a nontechnical compromise, but it was not risky and it worked. The voltages on the secondaries dropped appropriately. The path was now clear for further experimentation.

The radio circuit has four stages. RF stage, IF stage, Detector stage and AF amplification stage. By now, I was well acquainted with the schematics and the various components. To begin with, I removed all the valves from their respective bases, except the two valves of AF amplification stage and after checking every connection, powered this stage. I touched the grid of the first valve with a screwdriver and heard a loud distortion on the speaker. That was a good sign. The AF amplification stage was functioning. I then connected AF output of my FM autotune tiny radio to the grid of the first valve of AF amplification stage through a capacitor. Wow! I was listening to my local FM station clearly and loudly on my Vintage Valve Radio. It was a very unique confluence of modern most IC technology and about a century-old Valve technology working in unison!

Having gained confidence now, I inserted all the other Valves in their respective bases and checked all the other three stages to make sure that there was no short connection anywhere. I used a loop antenna mounted high on the terrace for better reception. I knew that Radio waves are best picked up at night. Hence, for the first time, I powered the Radio at night. To my utter disappointment, I drew nil. No Radio station was heard on any of the bands. After a lot of experimenting that lasted for a few weeks, I was convinced that the fault was in IF stage. Nothing was possible to do now. As a last resort, I finally bypassed IF stage using a crude homemade capacitor. This was the only and audacious compromise left for me to go close to my aim. Arriving was a ‘wow moment’ again. I could listen to a few powerful Radio stations late in the evening on almost every band. The Radio waves were finally ‘caught’ on my Vintage Valve Radio, nonetheless, with Hobson’s choice!



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