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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You may check on his previous repair article below:
https://jestineyong.com/burst-capacitor-and-bad-strip-wire-found-in-igold-dvd-player/
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Paris Azis
July 8, 2020 at 6:47 pm
Hey Parasuraman
Thank you for refreshing good old memories of mine,from the vacuum tube era!
Parasuraman S
July 8, 2020 at 9:52 pm
Many thanks! It is always a pleasure to work on antique sets!
AdamS
July 8, 2020 at 6:52 pm
Another superb repair, Parasuraman, but I would be careful about using WD40 for cleaning electrical switch contacts and controls. Whilst it frees things up mechanically, it leaves a residue behind which can do more harm than good to electrical parts and can actually damage potentiometer tracks.
It is much safer to use a proper switch cleaner like Servisol Super 10 or Caig Deoxit.
Parasuraman S
July 8, 2020 at 9:54 pm
Many thanks especially for your caution! I have been using WD40 for many years now to clean switches and pots. I have never come across any problems due to that. Anyhow, let me watch for such instances and report if found!
Humberto
July 10, 2020 at 11:17 am
Iñve been using WD-40 for many years with great results. This product has dielectric features.
AdamS
July 21, 2020 at 7:17 pm
That's precisely why it's bad - you don't want a dielectric (insulator) added to your potentiometer tracks!
Andrew F. Ali
July 8, 2020 at 7:58 pm
Thanks got that wonderful adventure. I learnt electronics on valve TVs in '72. Good job.
Parasuraman S
July 8, 2020 at 9:54 pm
Many thanks! Yes, Tube always drives to our Kindergarten of electronics!
New man
July 8, 2020 at 8:17 pm
Very excellent work !
Congratulations !
Parasuraman S
July 8, 2020 at 9:55 pm
Many thanks for your support!
Albert van Bemmelen
July 8, 2020 at 10:32 pm
Unlike most of the commenters I started when tubes got replaced by semiconductors and IC's. But I agree with you guys that the warm sound of those old tube receivers gives radio a special sound. But if I would use tubes today it probably would be for making powerful transmitters. Why those big watercooled mega sized tubes are still used in today's TV and Radio stations.
Parasuraman S
July 9, 2020 at 12:02 am
Vacuum is going to come back as miniature and microscopic tubes to be used in computer, because of its advantages. Many of its advantages were compromised when the world switched over to Discreet components. That's why the Transmitting is still using the Valves. Many professional studios use Tube Preamp, Tube Microphone and many such other devices, because of its quality reproduction. Many thanks for your comments!
Humberto
July 10, 2020 at 11:14 am
Till 80´s vacuum tubes were used in Military Stations, I don´t if they are still used nowadays with Military objectives.
Randy
July 9, 2020 at 12:20 am
Not sure if that was a question, but from what I was told is that the reason for tube finals in transmitters is that they can withstand lightning strikes better than transistor finals. This is particularly true in the American Southwest, not sure about other areas of the world. FWIW
Parasuraman S
July 9, 2020 at 3:19 pm
In almost everywhere Tube is still used.
Albert van Bemmelen
July 21, 2020 at 9:57 pm
Those mini radiotubes you spoke of Parasuraman, existed already in the sixties of the previous century.
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