Replaced IFT With Imported In PHILIPS Valve (TUBE) Radio Model MAJOR
A referred customer brought this Radio to me from a faraway distance. He was after me for a few months as my bedroom-converted-workshop was not having enough space to accommodate this large Radio. This customer was yet another who was fond of antique collections. This Radio belonged to his dad and he got the damaged cabinet redone in Teak Wood. So, the Radio was indeed very heavy, but not as heavy as a CRT TV. The complaint was low output and Radio stopped working. I also learnt that the radio was given to one of my techie friends for restoration long ago. It was lying with me for many months, as I was not getting time to pay an exclusive attention to this Radio. Then, under mild pressure from the customer, I took it up and opened the back and bottom cover. This is the advantage with Valve Radios of the yester years. We can just open the bottom cover to work on the circuits.
The set was coming on with low sound, but no radio pick up. I checked the continuity of the two IFTs and found one with open primary. In the other, the internal resistance of the coil was too high. The normal reading should be around 5 to 7 ohms. The peaking capacitor was also showing out of range values. The normal value should be around 195Pf to around 210Pf. Let us have closer look at the bottom connections of the two IFTs and its internals and measurement values:
The first two readings are that of the coil and the other two are that of the capacitors inside the IFT. One was showing 0.074nF instead of 195pF which is an indication of shorting. As you might perhaps notice in the last picture of the first row above, the IFT has two coils in each, with peaking caps connected across. The ferrite core is inside the tube (former of the coil) which is fixed to a metal screw on the top. For IF alignment we need to adjust the screws (turn it in or out) to get a proper output waveform of 452Khz at the output. These IFTs are normally fixed with carpenter wax and any attempt to open or adjust will in all probability detach the ferrite core from the metal screw, making it impossible to do any more alignment. Then we need to desolder the coil and capacitor from its legs and carefully dewax and take the former out to insert a needle to take out the detached ferrite core, the thickness of which might be similar to a hair of the elephant tail.
The best solution is replacement. But these IFTs are no longer available. Any attempt to rewind the coil which is like a human hair, is extremely difficult and an intricate, time consuming job, with no surety of success. I have done such cumbersome work before. But with age catching up, I was not confident of undertaking such a job again. So, I made another attempt to locate equivalent IFTs across the globe. One of my friends in the US came to my rescue and helped me get 16 IFTs which can definitely be used in place of these antique IFTs. I am giving below the pictures of the IFT imported:
The internal circuits of the IFT, how to modify and connect this to the Valves and suggested test are given below:
I connected one 101/2KV Cap from the first IFT to the second IFT. Both the IFTs have 200pF caps in its primary for peaking the tuning. As you will notice from the first diagram, one end of both the primary & secondary coils are shorted and B+ is applied to that point. The output is connected to the primary of the second IFT coupled with a 100pF Cap.
Both coils of the second IFT are also interconnected in the same way and connection for AGC taken out. I took a piece of PCB , drilled appropriate holes in it. I pressed bottom of the IFT on a piece of paper piercing holes and kept that paper on the PCB for drilling the holes in correct positions. Now, let us have a look at the finished product:
The red wire is for providing B+, Orange is the return end to the Anode of the input valve, the Green wire is for AGC and Blue wire is the output to be connected to the control grid of the output Valve. Then checked the connections in my Oscilloscope, applying 452KHz signal with modulation. I am providing the output wave forms both with modulation and cutting it. The wave form you see at the bottom (yellow) is that of the input and the one on the top is the output:
I am sure you all would have noticed the gain even without the amplification of the valve. Then wired the IFTs keeping them in the vacant slots of the old IFTs and used double sided stickers to fix it firmly.
Then powered the Radio, and applied 452KHz signal to pin 2 of the EF89 valve. Then tuned the IFT to its peak. Then did the same on the other IFT also. I did not use the oscilloscope to check the wave form and relied on my hearing as usual. After tuning the second IFT also to its peak, repeated the alignment on both the IFTs for proper peak output.
While doing so, we need to select Medium Wave Band and ensure that the gang was fully open (The needle on the dial is on its extreme end, at lowest frequency). Then when I looked for pickup of stations by slowly turning the tuning knob, AIR Thrissur Station was heard with crystal clear voice! It was a very pleasant experience and success of an effortful job!
As major restoration work was already done by my techie-friend, and all caps and resistors were also found ok, with appropriate voltages at the pins of the valves, there was nothing more to be done on the Radio. Here, you can have a look at the finished Radio with its light and magic lamp on:
Mission accomplished with antique satisfaction getting added to its collection!
This article was prepared for you by Parasuraman Subramanian from India. He is 74 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 Surprised Finding Haier TV Model LE32B7000 Working Well With A Bulged Cap Inside!
(44)Dislikes
(0)
15 Comments
Leave a Reply
Kevin Davison
October 5, 2024 at 5:54 pm
Absolutely brilliant once again, friend. This is a repair the likes of which I would have been unable to achieve and I enjoyed reading of your success. I thoroughly enjoy your detailed sharing of your repairs and this did not disappoint. Congratulations on another job very well done.
Parasuraman S
October 5, 2024 at 7:27 pm
Many thanks for your detailed comments and appreciation, dear Kevin!
Albert van Bemmelen
October 5, 2024 at 7:08 pm
As usual a very detailed explanation of all the hard work that needed to be done to get this old tube receiver fixed. With funny sidemarks as mentioning " the thickness of which might be similar to a hair of the elephant tail".
I therefore won't be able to exactly grasp the right thickness of the part you mentioned with descriptions like such. Please know that elephants in my country are very rare! (LOL).
Parasuraman S
October 5, 2024 at 7:31 pm
I request you to visit a nearest zoo, if they have an elephant or go to any circus tent if any, where an elephant is usually an artist. Then try pulling its tail to check how thick the hair is! (LOL) Anyhow, jokes apart, the hair of the elephant tail would be like a black tag that we can see used for tying the mains cord or other cords when bought new. Hope you will now get an idea. Many thanks for your keen study and expert comments, dear Albert!
Ajay Kumar, Puducherry
October 5, 2024 at 7:11 pm
Great job Sir
Parasuraman S
October 5, 2024 at 7:31 pm
Thanks, dear Ajay!
Yogesh Panchal
October 5, 2024 at 11:01 pm
Such an inspiring work,thorough technicians will know how the booster coil (you) works in the circuit (our community).
Parasuraman S
October 6, 2024 at 5:33 pm
Vow! A pleasant comment with deeper meanings! Many thanks, Yogesh Bai!
Mark J
October 6, 2024 at 3:34 am
Parasuraman thank you for sharing this great article. Well done.
Parasuraman S
October 6, 2024 at 5:33 pm
Many thanks, dear Mark!
Henrique J. G. Ulbrich
October 6, 2024 at 10:10 pm
Great, Parasuraman. Thanks for sharing and for remembering me the beautiful old times servicing antique tube radios.
You said the IF frequency is 452 kHz, but in general is 455 kHz. Is it correct?
Another thing is related to the IFT part “double” circuit. Generally there is no coupling capacitor, as the coupling itself is performed only inductively. Looks like two IFTs are used between the two valves, coupled with a 100 pF capacitor (I suppose the first valve is the mixer). For me, this is not so a common circuitry.
You tuned the IFTs just by hearing, not with the oscilloscope or another measuring instrument. I used to do the same way, and the results were always good.
Jayakumar.P.
October 6, 2024 at 10:23 pm
Sir,
Great work.Your style of writing needs special appreciation.Keep writing.
Thanks
PHILIP
October 7, 2024 at 5:34 am
I cant thank you enough, Parasuraman. In our country artisans and technicians are called liars because they dont mostly keep their promise to work on clients items, so cients dont always believe what they say. Parasuraman, I do repair small radios once in a while but the set up of the antique radio and the explanation of how the repair was carried out left me mostly overstretching my imagination so as to grasp some little techniques. Hard as I tried to be on the same page with you I only half understood the artical. Not even zooming the photos helped me gain much. Well, understandably, I have never stepped in an elecronics classroom. But if I may ask, how could all the two transformers call it a day and why must they be two? No mention of their output voltage, you never know I may soon be in need of one of the 16, especially if its adjustable.
Waleed Rishmawi
October 7, 2024 at 1:40 pm
that is an intensive surgery process you have just shared with us. I congratulate you on such repair and success. thanks for sharing and have a blessed day my dear friend.
Natarajan
October 15, 2024 at 9:37 pm
Dear Sri Parasuraman
Thanks for sharing a IFT replacement/fixing a problematic one.
I used to recollect when I was learning through Sri Govindaswamy of Chennai
Gemini Institute.
Time and again I insist there should be an Institute in India like
Novatech. Hope Mr.Jestine will take some efforts.