Another Thrilling Antique Valve (TUBE) Radio Service – AIRVOICE 2612
This set was brought to me by a recently added customer with the complaint that the Radio was not picking up any stations now and only some ‘drrrrr……..’ sound coming out. When I switched on the Radio in front of him, the complaint reported was found accurate. As he knew that I always try my best to bring the set back to its original working condition, he requested me to do anything that is found essential. Well, this is what we need from a customer as a support to go ahead with our service. So, the kick start was good and I removed the chassis out and subjected it to a thorough cleaning. Afterwards, I marked the valve numbers on the chassis at appropriate places in order not to mix up while replacing. Then removed the valves one by one, remembering to write the Valve number with a permanent marker on the valves.
This is very important as while handling the valves, the original print would get obliterated and we would end up with a misfit. Though the Valves are E series and pins 4 and 5 are common filament pins, other pins like grids, cathodes etc. might vary. In this Valve Radio, EZ80 was used as Rectifier, EL84 as output, EBC81 as preamp, EB89 as inter IF, ECH81 as the oscillator-mixer, and EM84 as the tuning indicator. Perhaps following circuit that I still preserve from my learning lessons when I was studying for Diploma in Radio Electronics way back in the 1970s, would help us all to refresh:
You will not find the connection of EM84 in this, but will find a lot of scribblings by me!
My first step in servicing such old sets was to look for strained components and tampering. This radio had undergone service before, as I found fresh wires connected to the mains isolation transformer. The customer confirmed that it was rewound and handled by another technician in a faraway place (known to me too very well!) I did a cold test of each and every resistor, fixed capacitor and electrolytic capacitor and found around 90% of them out and some resistances showed even double the value! AS these would certainly affect proper performance of the set, I replaced all such components. The initial collection of the defective components was like this, though a few more got added later:
After doing this exercise, I cleaned the pins of the valves thoroughly using a metal brush and made it shine, removing the fungi formations. Then sprayed the sockets with CRC2-26 and pushed/pulled the valves in/out gently to clean the contacts thoroughly. This has to be handled very carefully and gently, lest the pins or valve itself should break. After satisfying with the work done and rechecking for any overlapping or touching open wires, I applied power and checked the voltages at the Valve pin bases. These were found very accurate now. This step also is very important to isolate the stage of trouble. Checked the continuity of the IF transformers too. Now let us have a look at the inside of the set after the work and a few other relevant snaps: (Please use cntrl+up/down arrow to zoom in/out)
As the radio signals were not coming out in spite of all these efforts, I suspected a weak or defective valve. First I replaced the ECH81 valve and then the signals were picked up, though weak. When I tried to re-align the IFTs, it was not reaching the peak. So, I removed both IFTs and replaced the 100pf Caps and put these back. The IFTs were made by Universal, Japan. I used Philips IFT tuning kit for re-aligning the IFTS.
I fed a 455Kcycles modulated signal and once again tuned the IFTs for a peak output. The method is to move out the core to the outer side to the maximum, apply signal through a 0.1uF cap to pin two of EF89 and start turning the screw of the inter IFT secondary first and reach a peak. Then turn the primary to reach a peak. Then apply the signal to pin 2 of ECH81 valve, turn the secondary to reach a peak sound and then adjust the primary. Then retouch all the four screws starting from the first to last until a satisfactory peak sound is heard. Those of you who are interested in learning IF tuning may please visit these very useful sites: https://antiqueradios.org/gazette/align.htm and http://vrps.org/documents/Alignment.html [The second one covers almost all stages of valve radios]. Though I used a Signal Generator and oscilloscope to align, I forgot to click the snaps. Then the outputs of Radio Signals were very good. As there were a lot of interferences, I fixed a 0.001uF/1000V DC paper capacitor at the input of 230V, across the two terminals, behind the AC on/off switch + Volume control potentiometer. I noticed that the previous technician had overlooked the wiring of AC input to the rectifier valve which was located at the other side of the Chassis.
The AC wires were very close to the RF coils which would definitely create interferences. So, I rewired it through the top, provided a thick sleeve, and added caps and a coil like that we normally find in the AC in area of SMPS circuits of LED TVs. That was an improvisation experiment and it was found very useful. I used X type caps and a sturdy coil. The fuse we normally find at the AC In was missing and I provided an Automobile B+ high amp fuse holder, housing one 1.5A fuse. Now let us look at some more pictures as a help to understand the descriptions better:
With these modifications, the disturbances got reduced drastically and when a good outdoor antenna wire was connected, the tuning of radio stations was too good. I also provided a rubber bush to the AC wire where it entered into the chassis to avoid its direct contact to the metal. This was also missing! Then I took two RC jacks, shorted the inputs and soldered two wires with crocodile clips to provide an Aerial and Earth to the set.
The Radio was tested for several hours before giving delivery to the customer. He was so happy that he shared a video of its playing with crystal clear sound output. He was so happy that he shared the video of Radio performance before coming to me and after my refurbishing efforts with his friends.
Now, I have a lot more enquiries for such restoration works. A satisfied customer can bring in hundreds of other customers, like chain marketing! Mission accomplished very well and great satisfaction got gathered as usual!
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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