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Restoring a 50 Year Old Philips Radio
This lovely Philips Shipper Radio (RL557) was brought to me by a very close friend, and a Movie Music Director of yester years, who has been instrumental in bringing the best out of me, ever since we met a few years back. He is such an expert in Audio that I learnt a lot and lot from him. He has brought several of his friends as customers for me and the articles you read are mainly from these. He had picked it up from his friend’s house, where he saw it lying neglected. As he is an admirer as well as collector of antique pieces, he won’t let such sets go waste.
This was first brought to me in June 2015, for fixing a new TRA as its original had broken. That time, I opened the set, cleaned the inside thoroughly and lubricated controls. Even though it had motor boating sound at the time of start-up, he was reluctant to let me put my hands on the PCB for fear that the original lovely tone of the Radio should get affected.
As the set had facility for external DC supply, and replacing the 5 large batteries was a costly recurring expense (though Radio always work better in batteries), he inadvertently inserted an external DC adaptor, without checking the polarity specified for the set. There was no marking of it on the cabinet; either it got obliterated or was not there. He assumed it was standard, positive inside and negative outside. Then the set became dead and it was brought to me again in the middle of July, 2015. I opened the set and studied what went wrong. To open the set, we need to remove screws from the back as well as from the bottom. Just have a look at the construction of this set:
The output transistors were found shorted (AC187/188, which were germanium transistors, commonly used for push-pull stage where an output transformer, sometimes with an input transformer too, or complementary symmetry circuits in those days. Small power Amps used AC127/AC128). As I was not having replacement, I tried using AC127/AC128 bought from the market, which were of silicon. But not only did it produce a very bad sound output, it was getting hot. So, after consulting my friend, who reluctantly agreed to my suggestion for replacement of all electrolytic capacitors, I removed all the components from its output stage and provided a readymade TBA820 audio board in its place.
When I tried the tuning stations, only hissing noise was coming and no stations were picked up. I checked up and found that BF194B, a transistor used in the first end section of RF for oscillation and mixing was defective. Replaced it. Then also, no signals were picked up. Looked like the wrongly inserted adaptor had caused more problems within, than that could be envisaged. Then after consulting my friend, who only wanted MW local stations to be picked up for listening to the news by his wife, I realigned the set using my signal generator for 455Khz. I also replaced a few fixed capacitors. Here are a few more pictures after I did the modifications:
After ensuring that the set was working well, though the audio quality cannot be compared to its original condition, I delivered the set to my friend. But in came the set within a few days, as my friend could not tolerate its sound quality and moreover, the station pick-up itself was having distortions in it (developed later). As he dumped the set back to my workshop, I opened it and checked it up and noticed that the problems could not be easily resolved. So, I too got vexed and dumped it in one corner! Weeks, months and years passed unaware, until recently, on my periodical cleaning up work, I noticed this set lying in the rack, along with the five removed batteries on the side. The batteries were drained and rusted, but not leaked. So, I retook it for fresh study and attack on the problems reported. I replaced a few more fixed capacitors in and around the RF area and re-aligned the set once again. The output was very good. I replaced all the OA79 diodes, with IN4148. These were used in IF section as well as in the detector section. As the audio quality had got affected, I replaced the TBA820 IC also. The set then worked very well to my big relief. I spent money from my pocket to replace the batteries, damages of which were caused because of my sheer negligence. I also removed the Tone and Volume sliding controls and cleaned it up thoroughly.
Then it was time to put the dial cord back! This time, I had removed it for detailed study and rectification work in the RF area. I had drawn a diagram in my service data book (I use the last pages for such purposes, and give reference number of it there, and also mention it in my notes) which helped me. But you just see how complicated this process is. First you have to tie the cord on the Gang driving wheel, then take it out in proper direction, after winding it to the required number of turns, then on each of the guiding wheels, which are dual, one small on top and large at the bottom, we need to wind number of turns on each of these wheels, and then take it to the next, repeat this process, and then wind on the tuning spindle to the required number of turns and also follow the directions such that when the tuning spindle is turned clockwise, the needle moves from bottom to top and vice versa (i.e., from lowest to highest frequency; gang fully close and fully open). Well, like it was said many times before in this forum, why did the manufacturers complicate the needle movement so much, is something they only know. Especially, it looked as though Philips was doing it intentionally not only as a show-up of their engineering skills, but also as a masterpiece! Anyhow, back to this set, then the dial has to be fixed on top, and the needle on top, in its notch, by pulling the string up. Then we need to place the needle to such a position that it touches both ends with equal margin, and the stations are tuned as per markings on the dial. Well, we may have to try, try it again until we succeed! Have a look at the pictures and decide yourself:
Then fixed the DC input jack as it was before. Noticed that the spring of the (-) side of battery compartment was loose and it made a bad contact. Moreover, the plastic base on which it seats had cracked. So removed the spring unit, which has the positive contact at the other end, fixed the plastic portion properly using Fevibond first, using soldering iron, inserted cut leads of components to strengthen that portion (like re-inforced concrete that uses steel rods). Then inserted the battery connection unit in its place, applied one more coat of Fevibond and fixed it further with superglue and allowed it to bond very well. After an hour or so, fixed the back cover and tried to load the batteries and then I realized the stupid thing that I did. I had inserted the spring on its wrong side, i.e., the spring should be on the inner side and + side at the outer.
But I had overlooked it and had inserted it in wrongly. I tried to shake it off, and it never budged, and I was happy that it was so strong now. Then I removed the spring from its holds and fixed it at the bottom, after scraping the surface for soldering and soldered it very well. I also added small piece of tin sheet for enabling the + side to have proper contact. You can have look at my clumsy work, but with successful results from the only one picture that I remembered to click finally! Let me share with you, the result was better than the original!
Thus the avaricious ‘satisfaction list’ swallowed one more!
This article was prepared for you by Parasuraman Subramanian from India. He is 69 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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