Restored A Tampered And Spoiled KREFT Valve Radio
Those of you who have missed by earlier article published on 7th June, 2018 may please visit this link: Servicing Kreft Valve Radio | Electronics Repair And Technology News (jestineyong.com)
This radio was brought to me with the complaint that some bizarre sound was heard and radio was not working. This was reportedly lying unused due to a renovation in the house. I removed the back cover and did a general cleaning and powered it up. I was shocked to see that one valve was lighting up like a bulb, which I have never seen in my life time. I switched off the set immediately.
I removed the valve and when I looked at the bottom of the set, I knew immediately that someone had tampered with the set. There was no Rectifier valve in this Radio, as can be seen from my previous article as two diodes were used in its place due to some modifications done by previous technicians.
But someone had inserted a defective EBF89 valve when the Radio was not found working, assuming it could be the reason. I also saw that the dial cord was missing along with its spring and a tape recorder belt was placed between the tuning knob and drum of the gang! I observed that the rubber bushes holding the gang were also melted and shrunk, upsetting the position of the gang, as a result of which the dial cord could have got slipped out. The diodes were found to be partially leaky and the B+ was dropping heating up the mains transformer. I replaced the diodes with RL207. Also replaced a couple of resistors a few burnt resistors. Fixed the Gang with new bushes. Tied the cord for needle movement, for which I had to really struggle a bit.
I lubricated the band switch and also the volume/tone control potentiometers. Powered the set for a few minutes and checked that the audio was ok, by touching the input of volume control. Lubricated the valve bases and inserted the valve in and out for cleaning up of any fungus collections and to clean the contacts.
Then switched on the set and adjusted the padder capacitor of MW while turning the gang to get peak output of the local station. The radio was found working very well. We all know how difficult it is to service a set when it is tampered and spoiled by unskilled hands. My first job was to find out whether any alterations were made! Luckily there were none. Anyhow, I tested the Radio for several hours and did not find anything wrong. Mission accomplished and satisfaction generated got collected to its heritage!
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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You may check on his previous article on ATX SMPS Repair
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Jeffrey
August 27, 2021 at 1:52 pm
Amazing it still works and that you were able to find replacement valves to make it work again, I saw this vacuum tubes on TV sets when I was in high school but seldom in radios. The oldest I experienced repairing was a national radio using germanium transistor but this one is a grand daddy of radios
Parasuraman S
August 27, 2021 at 10:26 pm
Many thanks for your comments!
Yogesh Panchal
August 27, 2021 at 3:25 pm
Reviving antique Equipment like this is really thrilling job.
this is the only possible task by antique professionals like you.
Parasuraman S
August 27, 2021 at 10:27 pm
Many thanks for your comments, Yogesh!
Waleed Rishmawi
August 27, 2021 at 3:50 pm
I really commend you on such repair. I do not have your patients to work on such old devices. a job well done and have a blessed day
Parasuraman S
August 27, 2021 at 10:27 pm
Many thanks for your comments, my dear friend!
Albert van Bemmelen
August 27, 2021 at 6:06 pm
I guess that even if all coils and trimmers were tampered with you still do have the right measuring transmitter with about 455 KHz frequency to calibrate the AM (MW band) receiver (and possibly also 10.7 MHz for FM) back to its original settings.
Parasuraman S
August 27, 2021 at 10:28 pm
I do have an AM Signal Generator which I use for aligning the Radios. Many thanks for your comments!
Peter van Beveren
August 28, 2021 at 8:21 am
Nice repair. I remember using the once common tube testing machines located in various stores back in the day to fix TV's and tube radios. Many times pulling all the tubes out and checking them in the tester machines was enough to repair a faulty TV or radio.
Parasuraman Subramanian
August 28, 2021 at 3:50 pm
Many thanks for the comments!
Carlos Bielli
September 5, 2021 at 1:36 am
Some years ago I had a tube B&W TV with two silicon diodes for the main rectifier. One night, when viewing the TV the diodes burnt and shortcircuited the secondary of the power transformer, burning it and producing a lot of toxic smoke. After disconecting the TV and evacuating the smoke, I disasembly the power transformer, rewing it and installed new diodes with a fuse in series with each one.
Carlos Bielli
September 5, 2021 at 1:38 am
NOTE: This was in Argentina.7