Resurrection of a Philips Prestige Valve Radio

By on January 8, 2016
Resurrection of a Philips Prestige Valve Radio

 

 

 

 

 

 

 

 

 

I keep getting antique pieces such as Valve Radios, Valve Amplifiers, Valve Spool Tape Recorders etc. For servicing. In fact, this is what I like the most, being my favourite! I got one Philips Prestige Valve Radio 15RB/505/00Z. This belonged to a Public Library at a place around 20KM away, and was abandoned in their attic for many years, as there was none who could service it, until they came to know of me. The cabinet was in a bad condition.

The back cover was missing. The needle was missing. As, usual, my first job was blowing out loose dust, dismantling the unit from inside and do a thorough cleaning with my various brushes. We should never remove the valves from its basis, while cleaning this way, as the dust will get into the base holes. Then I brought it onto my work table for a detailed study. Removed the valves in order to tilt the chassis for bottom view. Did some more minute cleaning and wiping with cloths. The Valve numbers you see below are EZ80 (Dual Rectifier), ECL82 (PreAmp+Amp together), EBF89 (IF amp), ECH81 (Osc and Mixer) and EM84 (Tuning Indicator).

Resurrection of a Philips Prestige Valve Radio

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Observed that the Mains Transformer had burn marks and the thermal fuse inserted into the coil is open.

transformer coil open

Removed it and gave it for rewinding to my friend, as the primary was short. On doing cold test on the components, noticed that in the B+ rail, 1.5K 5W dropping resistor mounted on the output transformer was cracked and open. Similarly one 18K resistor at the secondary B+ was reading more than 24K.

multimeter

ESR of the 32+32mfd/450V Capacitor was perfect! One coupling capacitor was found cracked. So, I replaced these three components. Checked the IF transformers for continuity. Noticed that the primary of oscillator IFT (intermediate frequency transformer) was open. The secondary was showing around 7 ohms. In the second IFT (Detector side),  both were showing the correct ohms reading,around 7 Ohms. But on the secondary side, the ferrite core was loose. It slid in when I tried turning it. So removed both these IFTS. This is a tough job. The soldering iron cannot be inserted into the area, as there are several criss-cross wiring. So I noted down the wire connections in a slip of paper and cut the wires and removed both IFTs.

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The first one you see is a UNIVERSAL IFT released by Philips as a general replacement of all their IFTs. The second one is its original IFT. This indicated that some mechanic had replaced the first IFT. See below to know what is inside the Large IFT. Also side views and the tech details of Universal IFT:

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Since I had the circuit diagram of this model, it was easy in tracing the circuit for checking its various stages. I have repaired several Philips Valve Radios with the same circuit diagram.

valve schematic radio

I dismantled the small IFT and removed its ferrite cores to view the coils.

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Removed both the coils one by one and removed the primary and secondary, noting down its length on my table. In this, the primary coil has one primary winding and one secondary winding, with only a few turns. The second coil has only one winding. The length of the second coil wire is slightly more than that of the first coil. Took the coil to a coil winding shop run by my friend, who checked and found it was 44 SWG. He had only 45 SWG. So I took it, came back home and hand wound the wire on its tiny former.

tiny coil

Did the same for the other. Fit the coils back on its place. Soldered the leads to the terminals. Since the wire has enamel coating, first we need to flash a lighted match stick at the terminal, clean it and then apply flux and touch with solder. Otherwise, it will not get soldered properly.Did a dry solder patch on the bottom of the IFT, inserted its cans with its side protection sleeves (to prevent contact of the terminals with the can), and soldered the cans at the bottom. Since the core of the large IFT had lost its grip, I replaced it with a Universal IFT from my antique salvage stock. Both IFTs were soldered with pieces of wire on all the terminals so that I can connect it at the bottom easily. Restored all the connections as per circuit diagram. Got back the mains transformer after rewinding. It has one primary and two secondaries. One secondary will have 240-0-240 winding (for B+ that goes to the Rectifier valve) and the other 0-6V winding (for valve filaments and dial bulbs). The primary is 0-230V.  This is a 1 A transformer. Fit the transformer in its place and restored its connections, providing a 2A fuse at the primary in place of the thermal fuse. Rechecked all connections, inserted all valves in its place. Switched it on, and got crackling noise at the speaker, indicating all was well.   Injected 455KC/s modulated signal to pin 2 of EBF89 and tuned the corresponding detector IFT for peak output(First secondary and then the primary). Sounded well. Injected the signal to pin2 of ECH81, then tuned that IFT also to the peak. Re-touched the detector IFT and Oscillator IFT, first secondary and then the secondary, to arrive at a perfect peak signal without any distortions.   While aligning like this, we have to keep the gang fully closed in MW position. Then connected an aerial and looked for any station. It was giving an excellent performance!

All the bands MW, Short Wave 1, 2 and 3 worked very well! There was no need for any RF alignment! All the valves were working very well!   The voltages were also perfect as per the circuit diagram! So, replaced the dial bulbs. (Caution: While checking the Valve Radios, always remove the dial bulbs, as we need to switch it on and off several times, which will blow the bulbs!) Fabricated a needle from a copper wire, by fixing, putting the chassis in, removing for readjusting the length, width, position etc. several times until it was a perfect fit and moved to both sides smoothly.

With the dial plate placed, I readjusted the needle so that it indicated the correct frequency marked on the dial. For this, we need to tune to a known station, and readjust the needle to the frequency marked on the dial. The pictures below are of the fabricated needle and checking its movement position.

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Fixed the dial plate and fixed the chassis in the cabinet. Switched on the set, and tuned to a nearby station, and listened to lovely songs!

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Since the library has only limited budget for servicing this radio, I could not replace all the capacitors in the radio and rebuild the cabinet to its original condition. Very unfortunate! Anyhow, job well done satisfactorily!
Those of you who are interested in antique valve radios, please visit these sites:

parasuraman

This article was prepared for you by Parasuraman Subramanian from India. He is 66 years old and has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company.

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You may check on his previous repair article below:

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27 Comments

  1. Paresh Pai

    January 8, 2016 at 4:30 pm

    Congratulations to you Sir !
    Great job done and very well presented indeed !

    Cheers.

    Likes(3)Dislikes(0)
  2. Albert van Bemmelen

    January 8, 2016 at 4:33 pm

    Super repair Parasuraman Subramanian! Not many engineers do have the skills you have. I do own several original Valve operated AM/FM Radios but it is not my field of expertease. Or to repair these in the way you are more than qualified!! Although my Radios still operate perfectly and do not require any repair yet. I read some things about the ancient Transformers they years ago used that had also an extra wire connection for operating in the Tropics to keep the galvanic potential of the core intact. Or something like that. I probably have the article(s) about this as pdf file or still as very old magazine somewhere?

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  3. Mark

    January 8, 2016 at 5:44 pm

    Hey Parasuraman,

    Congratulations on an amazing job - as usual! Honestly, I wouldn't know where to start. You have years of experience that I admire. Please keep on sharing you articles and experience.
    I have started a multimeter collection and am trying to gain some vintage ones to create a full spectrum. Technology has come so far, but we do need to retain our electronic heritage.
    Thanks again.

    Likes(2)Dislikes(0)
  4. Robert Calk

    January 8, 2016 at 6:29 pm

    Nice job, Parasuraman. Would be better if so many photos were not so blurry.

    Likes(2)Dislikes(1)
    • Parasuraman S

      January 8, 2016 at 8:41 pm

      I would have loved to post very clear and sharp photographs. But I do not have a good camera with me. I use my Moto-E mobile camera. It is not good enough. The snaps you see a little blurred do not have any mild detail that would be useful to the readers, if they were clearer. Anyhow, let me find the budget to go for a good digital camera with zoom in it to overcome this perennial problem!

      Likes(1)Dislikes(0)
      • Robert Calk

        January 9, 2016 at 7:25 pm

        Hi Parasuraman,
        I use my digital microscope camera for most close-up photos. You can probably find one pretty cheap. Mine was less than $100US. I have a really good FujiFilm camera, but it isn't very good for close-ups. The microscope camera is much better at taking larger photos like a small component or PCB than I thought it would be before I bought it. I thought it would only be good for tiny things.

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      • Henrique J. G. Ulbrich

        January 9, 2016 at 10:26 pm

        Parasuraman, very good. Concerning the camera, what is important is that you must choose a camera with the Macro function (many cameras have it). The Macro function assures high focus even at too short distances.

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        • Parasuraman S

          January 21, 2016 at 11:32 pm

          I have solved the close focus problem in my mobile camera by using a watch repairers x3.5 and x10 lens, which I had with me. I keep it on top of the camera lens and adjust the focal length to get a better and clear photograph. You will find the difference in my later articles that would appear. You can notice a prominent difference. Anyhow thanks for your concern!

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  5. George Greenfield

    January 8, 2016 at 7:08 pm

    Started my career @ 17 working on a variety of Electronic devices. Hated working on tube (valve) devices then. Hot, heat damage, limited diagrams, obsolete parts. Have now come full circle. Now I like to work on tube equipment and not so much modern "junk".
    There is nothing like the glow of a tuning dial and the glow of the electron tubes.
    Great repair article.
    Thanks

    Likes(4)Dislikes(0)
  6. Henrique J. G. Ulbrich

    January 8, 2016 at 9:20 pm

    Nice, Sir. Many, many years ago I've worked so much in these type of radios. I've also made some needles as you described. I've also calibrated a lot of IF channels and so on. Your report makes me feel nostalgic. Good times! Concerning this model (Prestige), I don't remember of it. Perhaps this model was not distributed by Philips here in Brazil at that time.

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  7. Humberto

    January 8, 2016 at 11:05 pm

    Hi Parasuraman, you are a real Master. Congrats. and keep up.

    Likes(1)Dislikes(0)
  8. Merlin Marquardt

    January 8, 2016 at 11:54 pm

    Wonderful repair and article with links to other sites of interest in valve radios.

    Likes(1)Dislikes(0)
  9. Jayachandran Durganathan

    January 9, 2016 at 12:22 am

    Hello Parasuraman Subramanian,

    your presentation is superb, I have lot of valve radios that I like to restore,
    my father was one of the few radio Service engineers in our town of his time.

    I recently discovered 4 valve radios all are RF Tuned, from the attic, will contact you for your help, as my dad is no more...

    Regards
    Jayachandran Durganathan.

    Likes(1)Dislikes(1)
    • Parasuraman S

      January 9, 2016 at 8:08 am

      Dear Jayachandran: Thank you! I will only love to help anyone in repairing work, especially if it is of antique in nature. You can write to Jestine Yong to get my email address, as publishing it here might attract a lot of spams!

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  10. Albert Hoekman, Holland

    January 9, 2016 at 12:30 am

    Very nice and time eating job! In my younger days, about 55 years ago, I did also repair these bulb radio's and massive taperecorders starting with pieces from the hole family. Replace bulbs, the big black capacitors and resistors, adjusting cords (I still have a roll of this non stretchable cord), and the so called dialing bulbs. Cleaning with air and lubricating the ball bearings of the variable tuning capacitor. And so on. A very thankfull job as you know. The price of repairing one radio was 10 liters of fuel for my moped...

    Thanks for sharing this article.

    Likes(1)Dislikes(0)
  11. Parasuraman S

    January 9, 2016 at 8:10 am

    I thank all of you for your encouraging comments!

    Likes(0)Dislikes(0)
  12. Gerald

    January 9, 2016 at 9:16 am

    Hi Parasuraman,

    Wonderful, your article brings me back to when I started my electronics career, repairing valve radios and TVs. ECH81, ECL82 etc... sound like music to my ears. So many years ago but it feels so close.
    Your repair is just fascinating, so much patience and dedication.
    Congratulations and thank you for sharing.
    Cheers,Gerald

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  13. beh

    January 9, 2016 at 12:50 pm

    HI PARASURAMAN
    thanks for article .i want just to tell you this kind of old y radios if works are subject to Antique and are very expensive In my country much much more than new ones.
    regards
    beh

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  14. S Ramachandran

    January 11, 2016 at 12:39 am

    Dear Parasuraman ,

    Greetings to you sir, you have taken me to the yeaster years of repairs and still having the old universal IFts for philips value radios.

    good job done and now a days nobody likes to give a try ..

    you might have procured those spares from the very old radio spares distributers in ernakulam.. please share your repair articals and this can motivate the younger generations to save the products going to junk.

    with regards,
    S Raamachandran.

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  15. Gopal Sharma

    January 11, 2016 at 2:17 pm

    Congratulations sir. It is nicely presented also. I have very little knowledge about valves. But sound quality of valve radios are very sweet and memorable.

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  16. Parasuraman S

    January 11, 2016 at 4:40 pm

    Once again thank all of you, for your encouraging comments! This alone will keep me batting, not out!

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  17. Gerald Millward

    January 11, 2016 at 5:51 pm

    Parasuraman - A fascinating report. I am old enough to have built and repaired valve equipment (my first electronic effort was a crystal set in 1954). I had forgotten the spaghetti-like wiring under the chassis in valve equipment! I have to admit I find modern printed circuit boards and SMD componerts nicer to work on. But it takes dedicated technicians like you to ensure that these memorable examples of historical technology are not lost.

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  18. tana

    January 24, 2016 at 11:55 pm

    S Parasuraman, it is indeed a tough job. You are a wonder . You can do such tough job. I used to do valve radios and amplifiers in the 60s and 70s.
    Now all forgotten . Thanks for refreshening them . Good luck to you .

    tana.

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  19. Venkat

    August 31, 2016 at 1:46 am

    How many turns of primary n secondary winding in ift.

    Likes(1)Dislikes(0)
    • Parasuraman S

      March 27, 2017 at 1:27 pm

      I normally take out the old carefully, spread it out and take new wire of the same gauge and length. The number of turns actually is not an accurate way of doing rewinding, as the diameter of each round varies as we progress in rewind. If the winding is not tight enough, you will run short of the required length or vice versa.

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  20. Manoharan

    December 20, 2016 at 9:20 pm

    That B+rail resistor is 1.2k 5w. EBF89 is 2nd if amplifier and detector.Some bakelite cabinet sets (valiant ll) has 6"×4" oval speaker. This model has 6"round speaker. Good efforts ! I too seviced many sets with same circuit.

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  21. Vikram

    March 11, 2017 at 7:01 pm

    Thanks learned a lot from this

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