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Servicing Kreft Valve Radio
This valve radio was brought to me on 6th January, 2018 with the complaint that it was not picking up any stations, the band switch knob was broken and the dial chord had broken loose. As per my records, this set was brought to me on 20th June, 2014, with the complaint that Audio was weak. Then I had replaced around 20 components and aligned the IFT properly and gave it back in perfect working condition.
It did its revisit on 8th August, 2015 with multiple complaints. The main transformer was heating up and got rewound. EBF89 Valve was replaced. The Oscillator IFT was rewound. ECL82 Valve was replaced as I found it to be weak. So, this was making the revisit after a gap of around two and a half years!
After opening and cleaning it, I investigated the reasons for the failure. Noticed that B+ voltages were ok and the amplifier part was working. I gave signal to the aerial input socket and noticed that nothing was coming out. Gave the signal to the output IFT and got the signal. So, the defective stage was in the RF section. Checked the voltages at the pins of ECH81 Valve and found it to be ok. Replaced the valve with a working one. The set started working. But when I tried to retune the IFT feeding 455KHz signal, the ferrite core of one of the IFTs was not turning and the holding screw at the top was just going up and down, indicating that the ferrite core has come off it. So, removed the IFT, and opened it up. Fixed the core to its holding screw using less than one drop each of Fevibond and Superglue, after Fevibond dried. Allowed it to bond properly and put this back in its place. Re-fixed the IFT and retuned the Radio for proper peak signal. The Radio started working perfectly well. Tied the dial chord. Provided new knobs. Now here are the pictures of the Radio, along with the measurement of the ferrite core using Vernier caliper.
I took the measurement of the ferrite core for future reference to fetch it as a replacement, in case it gets broken. Sharing it for those of you who might require.
From the pictures, you can see the inside of the set very clearly. You can also see how the construction of the IFT was done those days. This is a very delicate thing to handle. You can also see the dial chord tied properly in its place. The magic Valve, which is a peak tuning indicator, is always an attraction in Valve Radios. The valve number generally used is EM84. In fact I like the flower type! In this Radio, ECH81 (Oscillator and mixer), EBF89 (inter IF amplifier), ECL82 (Audio pre-amp and power output together) are used. Originally it might have had EZ80 or 81 as rectifier. But that has been replaced with IN4007 diodes, as you can see from the bottom side of the set. This is a lovely set. Here, take a look at it after I replaced all the knobs. You can also see the defective valve and broken dial chord.
A job completed and added to my satisfaction bag!
(For more detailed explanation of RF and IF tuning and other Valve Radio related topics, kindly refer to my earlier articles.)
This article was prepared for you by Parasuraman Subramanian from India. He is 69 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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