Restoration Of Antique Philips Valve Radio Model 15RB525/11Z
This antique valve radio was lying in a shop and my two wheeler mechanic located it by chance. He picked it up along with another one, Model ARC. Both of them were just bare without the cabinets. This Philips Radio had no front dial glass even. The ARC had a dial glass, but was with a lot of missing parts including valves. So, the customer requested me to try restoring the Philips. You can see the remnant mud of white ants that ate up the entire wooden cabinet! My immediate job was to do a blower cleaning without using any hard brushes, as the coil wires might get damaged. I also cleaned and lubricated the valve bases.
When I powered it on, all the filaments were working! But there was no sound output. The B+ was good with the old electrolytic can capacitor itself. Looked for any open resistors and found a couple of them. As I had the schematic of this Radio, trouble shooting was easy. Replaced it and found the audio side working:
Then I traced fault in one of the IF transformers. I removed it and opened it up. Found the condensor defective (shorting). Replaced it with a 100pf.
The Gang condensor was shaking as its base was melted. So, removed it and placed new rubber bushes.
After refitting everything, I aligned the Radio feeding 455Khz Modulated Signal and tuned the IFTs very well for a peak output. Afterwards, when I tried, the Radio was working very well in all bands except one. In that the coils were found shorted and nothing could be done to restore it, as these were housed inside small cans and we cannot even attempt to remove it from the hardened wax.
The customer came and picked up the set for giving it to a carpenter friend, to do the cabinet making. After several months, it was delivered back to me for final adjustment and tuning, as was planned. This was lying in one corner as I had a lot and lot of sets, especially TVs coming in and I gave only last priority for this. Recently, when I took it up, because of the pressure from my mechanic friend, I was shocked to see that the ECL82 was broken and one pin was stuck inside the base.
The Mains Transformer had suffered damage as some sharp instrument scorched the windings. There were damages to the coils too! I informed the customer immediately, who requested me to do what best I can to bring it back to working condition. When I applied power, the B+ was dropping and the transformer got extremely hot and burning smell came out. I switched it off immediately, waited for it to cool down and removed the transformer for giving it for rewinding.
Though one of my techie friends dismantled the transformer and took count of the turns, he could not complete it as getting 39swg coil during this pandemic period was almost impossible. But another of my techie friends accepted the job, as he had the coil in stock. So, I collected the dismantled transformer and gave the winding details and provided it to the latter. He did a neat work and returned it after a couple of weeks. He could not fix the frames properly as he was not having bench vice. I used C clamps and held the sides tightly and fixed the frames. Then reconnected the transformer and replaced the ECL82 from my stock. Switched on and found the Radio had life left in it.
The radio worked well, though the meddling with the coils caused some disturbances and tuning problems. I tried my best to restore the Medium Wave bands. Retuned and made the best that could be possible given the circumstances and limitations. As the speaker was not able to deliver the load properly, I replaced it later.
I fixed the back cover with screws. Also fixed the bottom cover which had an opening for troubleshooting. The dial reflector along with the two bulbs were given to the customer, who came to collect the Radio.
He has to get it fixed outside with a suitable glass. I have no idea what all further damages that await this set! Anyhow, from my side the work was over and that was enough for satisfaction to jump into its collection bag!
This article was prepared for you by Parasuraman Subramanian from India. He is 72 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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