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.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
P.S-If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!
You may check on his previous article on ATX SMPS Repair