Restoring A Sharp JHANKAR Tube Radio 7A57
Make and Model: Sharp Jhankar Tube Radio 7A57
Complaint reported: Dead
Troubleshooting and restoration done: Opened the back cover and cleaned the set thoroughly. Observed that the speaker paper was worn out. Got it repaired by a speaker reconditioning shop.
Applied power and checked for DC presence on the rectifier valve, EZ80. It was low but ok. Turned the volume control to full and touched the signal input pin and got a loud noise indicating that the Amp section is ok, though there was disturbance and noise. Touched on the pin 2 of IF amp valve and did not get any output. So replaced all the coupling capacitors and electrolytic capacitors in the set. Then the signal from aerial input itself was good. Sprayed WD40 on the band switches, volume and tone controls ensuring that these do not get into the coils. Operated the band switches one after the other several times to ensure that the WD40 does the cleaning job. Turned the Volume Control several times to do the self-cleaning. Applied WD40 on the valve bases, then gently removed and inserted the valves several times to ensure self-cleaning.
Put a drop of WD40 in every socket from Aerial to external speaker connections, inserted a dummy pin and removed several times to clean each of the sockets. This type of cleaning will not only ensure that the fungus formations are cleared but also clear the oxidization. The metal will rub on each other to make the surface dirt free and shining. Turned on the set, connected an external aerial and tuned to a known frequency. The set was working well. Removed the Aerial. Set the radio to MW and gang in fully closed condition, fed 455Khz Modulated frequency to pin 2 of RF Oscillator Valve. Aligned the IFs to get maximum gain (First the Intermediate IF and then the Oscillation IF). Repeated this until the output was very good and noise free. Disconnected the Signal Generator and connected the external aerial and tuned into stations. Got very good output with crystal clear voice, bringing the nostalgic memories of the past. Appreciated the wonderful antique technologies with gratitude to those who developed it. Mission accomplished with bulging satisfaction getting added!
Here are a few pictures:
This article was prepared for you by Parasuraman Subramanian from India. He is 70 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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