Philips Novosonic Valve Radio Restored

By on February 18, 2016
Philips Novosonic Valve Radio Restored

 

 

 

 

 

 

Philips Novosonic Valve Radio Restored

I had got one Philips Novosonic Valve Radio in a very bad condition for a possible restoration from the same place where I had got another Philips Valve Radio a few weeks back. The cabinet was all in bad shape: No back cover, rat had cut many wires underneath including the power cord and dial cord, plywood at top and bottom were exposed and in layers, cone paper of speakers were moth eaten, medium wave coil was cut, but had all the valves in place.

 

First and foremost, as always is the case, I did a thorough cleaning of the inside with blower (watching a lot of paper pieces and other particles normally used by birds for building nest, flying away from underneath and sides), removed the chassis out, and did one more cleaning with blower and various brushes, and made it ‘qualified’ for entry into my service room! All blowing and cleaning should be done without removing the valves. Otherwise the dust will go into the valve base holes and it will be extremely difficult then to clean it.

Philips Novosonic Valve Radio repair

Philips Novosonic Valve Radio repairing

Philips Novosonic Valve Radio schemmatic

Since, I had the circuit diagram of this model with me, I removed all the hanging rat bitten wires by cutting these at the soldered points. The locking springs of the Bass, Treble and Pick Up Push Button Switches were rusted and spoiled. So I removed these wires also completely deciding to disconnect these. Then removed the valves one by one; EM84 (Tuning Indicator), EZ80 (Double Rectifier), EL84 (Power Amp), EBC81 (PreAmp), EF89 (Intermediate Frequency) and ECH81 (Mixer and oscillator).  Cleaned the pins of these valves with metal brush and made it shining. Gently wiped the dust from the valves ensuring that the valve numbers printed on it are not erased. Sprayed WD40 liberally on the valve bases, piano band switches simultaneously pressing the buttons one by one for effecting a self-clean of contact points, volume control, spindle joints of the Gang and its clutch wheels (ensuring that not even one drop goes inside the gang, lest it should affect the capacitance affecting RF frequency range. We should also ensure that it does not enter RF coils) and also the moving wheels of the dial cord. Allowed this to dry off overnight.

Connected a new mains cord and checked for continuity of the primary of the mains transformer. It was OK. Checked the secondary, both HT and 6V for the filaments and dial bulb. It was also OK.  Connected the wires to the mains and checked the AC voltages that should be present at Pin 1 and 7 of EZ80 valve. It was reading 240V each.  Checked ESR of the 50mfd+50mfd Can Capacitor. It was Ok. Switched off mains, inserted EZ80 valve and checked the DC output at pin 3. It was very low, only around 110V. Suspected problem with the Valve. Replaced the valve with a new one from my stock.   Same reading. So, I disconnected all the loads from the B+ and Secondary and checked. It was still low. So, I knew the culprit is the can capacitor, which is shorting when fed with voltage. So, cut the wires from the bottom and connected two 47/450 capacitors at the bottom.

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Connected to mains and checked the DC Voltage at Pin 3 of EZ80, it was showing 300V DC (A good valve, indeed!). Disconnected the mains, discharged the capacitors and checked the continuity at the primary and secondary of the audio output transformer.  It was ok. Checked the resistors in the B+ line. Found a few resistors burnt, value far above and saw one cracked coupling capacitor.   Replaced all these. Checked all other resistors and found these to be ok. Look at all the trouble making components and mess making wires removed:

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Inserted the EBC81 (preamp) and EL84 (Power Amp) valves.  Connected a pair of long wires at the output transformer secondary for connecting to a test speaker.  Switched on, waited, and got the consoling and pleasant audio hum at the speakers.  Touched the hot pin of the Volume Control and got a crackling noise, which means everything is ok in the audio stage.  Switched off and waited for the B+ to get discharged. Checked the primary and secondary of both IFTS. Found the primary of Oscillator IFT was open.  Removed the IFT, opened it, removed the coil and rewound it by hand as I did last time (Please see my earlier article on Philips Valve Radio Repair). Refit the IFT. Switched on and heard bursting and crackling noises, and noticed that ECH81 valve was arcing inside. Switched off immediately. Removed the valve. Switched on and again got the same noise. First I thought it was in some coupling capacitors or on feed back circuit. So isolated these one by one, but with the same result. So, my attention went to the valve base. Switched on and observed the valve base from underneath after switching off the table lamp. I could see visible arcing between pin 7 and 8. Checked voltage at pin 7. See what I saw, the meter was showing 223V DC present at pin 7, which should not be!

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Switched off. Checked continuity between these two pins.  It was infinite. Isolated all connected at pin 7 and checked again. The arcing was still there. So, concluded that the valve base is the culprit. Removed it and see how it looked:

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It was arcing only when the voltage was present though there was no continuity on cold test, because there was the dark burn marks between the two pins. This type of valve bases have layers and are very cheap and prone to develop leaks between pins, mainly due to loose contacts at the valve pins. So, replaced the valve base with a new one from my stock, and fixed it with mounting screws, in place of the rivet holes of the old valve base:

valve base

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Rewired its connections at the bottom as per circuit diagram, restored all connections removed for isolation purpose. Restored the MW antenna coil connections. Switched on. The set was perfect.  Waited for about half an hour to allow the set to warm up. Selected MW on the band switch, manually turned the gang to its fully closed position (all metal leaves inside). Tuned the Detector IFT by feeding 455Khz modulated signal via .1mfd/400V capacitor, at pin two of EF89, first secondary and then primary for a peak output. Then fed the same signal at pin 2 of ECH81 valve and tuned the Oscillator IFT in the same way, secondary first and then the primary, readjusted the detector IFT once again and again the Oscillator IFT and ensured peak output. Sealed the adjusting screws on top of the IFTS with carpenter wax. So IF Tuning was over. Switched off my computer, UPS and the tube lights in my room.  Went to the other rooms and switched off the Tube Lights there also, changing all lights to CFL. Otherwise Radio will pick up 50hz signals from these and we may not be able to tune to any stations. Connected an external aerial, turned the gang manually, and I was very happy to tune to various stations crystal clear in all the bands! There was no need for any RF tuning at all! The output was so amazingly awesome! The funny thing is that both the speakers, with most of the paper missing, gave a very good output! (Anyhow I got the paper patched up later by my friend who is running a speaker repair shop. He pasted a paper on top the old one, without disturbing the spider, and fixed the outer on the round frame)

valve radio repair

Now the next job was to tie the dial cord! This is a challenge to any technician! Luckily the circuit diagram showed the diagram of this too! But the problem was that the first part of the thin wire was cut to several pieces by rat and I could not find a replacement flexible wire in my stock. We cannot use any copper wire, as it will wear out soon and get cut. So I decided to forgo one part of the guiding outer sleeve, which has very narrow hole, and replaced it with a tough sleeve. May be due to my experience, the whole thing worked just fine with the first attempt itself! We need to ensure that when we turn the tuning spindle left, the needle should move to the left, and vice versa, at the same time ensuring that the Gang opens and closes at the places where the frequencies are marked on the dial! The frequency will be low when the gang is fully closed, so the needle should be at the extreme end where the MW frequency is around 455KC/s (about 450 Meter Band). When the gang is fully open, the needle should be around 1600KC/s (Below 200 Meter Band). When the IFT is tuned to 455Khz at the lowest capacitance, the IFT oscillations will be 50Hz lower than the tuned frequency, preventing overlapping of stations, and preventing howling, whistling etc. Those of you who are interested in learning more about RF/IF and alignment, working etc., please visit this website: http://www.vintage-radio.com/repair-restore-information/valve_alignment.html and http://www.vintage-radio.com/repair-restore-information/valve_if-rf-stages.html

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Replaced the front panel dial. Replaced the dial bulb, which I had removed earlier in order not to blow it off during my several on/off attempts. Placed the needle in the appropriate place after tuning to a known station and looking at the dial. Fit the chassis into the cabinet, through the front side. Switched on and the Radio was back in working condition!

philips radio valve repair

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Unfortunately, once again, this customer was also not having the budget for remaking the cabinet and provide a back cover! He said he would fabricate one back cover himself from any cardboard!   So, I had no other go, except to deliver the Radio in this condition! What else once can do? Anyhow, another job well done, though I had to spend several hours and sit for days together to complete this work! At least, I can claim that I spoiled the attempts of a naughty rat to throw the Radio to Electronic Waste Basket!

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:

http://www.jestineyong.com/sonodyne-scr2065-brought-back-to-life/

 

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23 Comments

  1. Mark

    February 18, 2016 at 9:12 am

    Hey Parasuraman,

    Thanks once again for a well written repair. You obviously have a skill for valve circuitry. To be honest, I probably wouldn't know where to start! I guess they were just the forerunners of ICs. Are parts difficult to find and are the testing methods different from what we are doing with semiconductors?

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    • Parasuraman S

      February 19, 2016 at 1:23 am

      Parts are extremely difficult to find, and if found, exorbitantly priced! But I have a lot of collections in stock, including over 200 valves. Testing methods are same, the valves have cathode, anode, grids, in addition to filament for heating up. Like a transistor base, emitter, collector, each of the above are supposed to show certain voltages present if the valve is good. Unlike transistor, you cannot check continuity, diode check or resistance between cathode, anode or grid. But filament can be checked with a multi meter for open. In fact, it is easier to trouble shoot Valve sets than other semi conductors, as we can remove the valve and check each stage without any desoldering!

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  2. Robert Calk

    February 18, 2016 at 10:20 am

    Lol - the rat lost! Nice repair, Parasuraman.
    Thanks for the article. I enjoyed it.

    Likes(1)Dislikes(1)
  3. Kevin Hall

    February 18, 2016 at 11:01 am

    Parasuraman, I wish you were my neighbor, we have lot in common, I have a collection of radios from childhood to now and cant find time to get to them. like you I am a BSEE and a consultant for 40 years. Wish you could contact me. I am in USA. My best wishes.

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    • Parasuraman S

      February 19, 2016 at 1:24 am

      You can always contact me through Jestine Yong, who has my email address.

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  4. Paresh Pai

    February 18, 2016 at 11:50 am

    Congrats for a great repair job! Very nicely executed indeed !
    Also very well presented. Thanks.

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  5. Suranga Electronics

    February 18, 2016 at 2:09 pm

    Thanks Mr- Parasuraman Subramanian,

    Your great repair work is very nice. For your information i can't repair this type of Valve Radio Device.

    Likes(1)Dislikes(0)
  6. Yogesh Panchal

    February 18, 2016 at 3:16 pm

    Sir,

    Enjoyed! Era of Technology,Experience and Passion.
    Thanks for Sharing.

    Likes(1)Dislikes(0)
  7. Albert van Bemmelen

    February 18, 2016 at 5:31 pm

    Thank you Parasuraman, and although I myself do not work with these Valves or old radio's anymore, I really appreciate the way in that you always take the time to repair these old dinosaurs. And thank you for the nice and very new looking schematic of this Philips Novosonic Radio. I still have a set of old valves laying around (given to me free) and one or two valve recievers. Which I keep because it is a shame to throw away something that is working just perfectly fine.

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  8. Gerald

    February 18, 2016 at 6:06 pm

    Wow, another fantastic repair Parasuraman. Congratulations and thank you for bringing me back to my earlier days as an radio-tv repairer apprentice. Btw redoing the dial cord was the job of first year apprentices... some of those were so complicated and sometimes we didn't have the diagram.
    Great memories.
    Cheers,
    Gerald

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  9. Paris Azis

    February 18, 2016 at 8:45 pm

    Good job Parasuraman. Thank you for refreshing my memory!

    Greetings

    Likes(1)Dislikes(0)
  10. Humberto

    February 18, 2016 at 8:54 pm

    Wow! Parasuraman you are a Master. Congratulations for your excellent repair, explanations and good photos. Keep sharing your experiencies with us.

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  11. Randy

    February 19, 2016 at 12:29 am

    I do (and have done) a lot of these old radios, although not the foreign sets like Saba, Telefunken, Phillips, etc. as these can (as you noted here!) be a real PITA with many issues due to cheap construction, poor storage conditions, old resistors changing values, bad coupling and especially E-caps, etc. As these are low value (except for some of the Majestic Art Deco sets from the '30s and the black dial Zeniths from the same time period), I generally stay away from them as no money to be made from those repairs! Still, I do a lot of vacuum tube electronics (Scott & Fisher audio amps, Fender guitar, etc.) and find that since they are valuable pieces, money can be made from them, which as someone with electronics background should be entitled to! So your article brought back many memories, some good, but some bad as I have had similar experiences with these old radios, good job!

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  12. Henrique J. G. Ulbrich

    February 19, 2016 at 9:56 pm

    Congratulation, Mr. Parasuraman! Another nice trip to my old times, when I performed too many repairs on valve radios. Thanks a lot. Just a comment: OK, you've found a bad e-cap, but we must take into account the AGE of this e-cap. It worked years and years and the fact is that ONLY NOW it was found defective. On the other side, the e-caps nowadays produced last a time considerably shorter. What have the chinese to say about?

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  13. Albert Hoekman, Holland

    February 20, 2016 at 1:28 am

    Mr. Parasuraman thanks for sharing this very good and well explained article. Keep on going!

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

    February 23, 2016 at 8:07 am

    I thank each one of you for your encouraging comments! It helps me a lot!

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  15. SAJID RAUF RAJA

    March 1, 2016 at 8:19 am

    Good Morning PARASURAMAN S.
    Frst of all I want to pay you homage with depth of my heart on such a marvellous job you accomplished. It was really extremely informative. This was recalled my RAM during my childhood,when my late Dad was troubleshoot similar such jobs in 50's to 80's. To quinched my desire I had asembed 7 valves 3 band radio receiver a kit bough from CHINA from above Web site. I have some queries 1.how calibrate dial? 2-how to proper alignment of all 3 bands? Shall you please look into tha how could we address above quires in right manner to bring it in best working state (bear in mind that at could tune in couple of statons at SW3 SW2 NONE and MW 2-3 STATIONS. I DO STRONGLY +VELY OPTOMISTIC YOU KINDLY RESOLVE ABOVE QUIRES.
    THANKS,
    KIND REGARDS
    SINCERELY
    MR SAJID RAUF RAJA.

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    • Parasuraman S

      March 7, 2016 at 9:14 am

      First of all thanks to you! From your query, I assume you want to make a dial, and calibrate it properly. For that, you need to have the technical specifications of the coils used in there and preferably that of IFT. IFTs are tuned at 450Ks to 460Ks, depending on the manufacturer and design of the set to get peak output without distortions. From the coils, you need to know what is the minimum and maximum frequency for which the coils are made. Then, keep the band switch in Medium Wave, (disconnect any outside aerial) turn the gang to fully closed condition, feed modulated RF frequency at 455Ks or as the case may be to grid of the Valve and tune the IFTs starting from detector to oscillator as described in the web link I have given. Then keep the needle there, and tune the RF frequencies of the MW RF oscillator coil, for lowest at that point and open the gang fully and tune its trimmers. Do the same for other bands as well. You may have to repeat it a couple of times to get perfection. Then keep tuning the radio by connecting the aerial and mark frequencies of known stations on the dial. You may have to tune to almost all stations if you want to mark it perfectly. This is a laborious and time consuming job! Pl remember that tuning the IFTs to its peak is the secret of getting all stations. All the best!

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    • Parasuraman S

      March 7, 2016 at 1:20 pm

      Forgot to mention that after aligning the RF Oscillator Coils, you may have to tune the Antenna coils. In the same method explained for RF Osc., tune MW Ant coil for peak of any station nearest to the closed gang position, and then open the gang fully and tune for any weak station nearby, then adjust the antenna trimmer for best result. Repeat this a few times, until you get very good signal at both ends. Follow the same method for SW bands as well. You can use RF Generator, if you have, and do the same at both ends feeding the signal as per specifications of the coils used. All the best!

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  16. Beau Friend

    March 4, 2016 at 12:55 am

    Greetings Parasuraman,I really did enjoy your article on restoring the old valve radio - great stuff. I'm currently doing a similar thing on a GEC valve set but don't seem to be able to find good info on valve equivalents - being an American radio design it uses a DH63 (ECC83?) audio preamp and KT66 PA (6v6GCT?) Any ideas where I may find this information? Much appreciated. Beau Friend

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    • Parasuraman S

      March 7, 2016 at 9:17 am

      Just type the valve numbers in Google search, you might find it there. Otherwise, look for my previous article on Valve Radio, where I have given links of certain valve specialists. Look through the data published there or put up a query! (Radio Museum is another site that provides technical info) All the best!

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  17. Graig Wynter

    March 13, 2016 at 8:53 am

    The wavechange switch is a large sliding wafer type which, although OK in this set, looks to be a likely trouble spot due to its flimsiness. This is mechanically linked to the rotary knob on the front of the case.

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  18. Susapta Ghosh

    July 6, 2016 at 3:05 am

    Respected Shri Parasuraman S,
    I am writing you from Kolkata, India. I am in search for a extremely good sounding valve radio (preferably with stereo fm reception} in fully restored condition. Should have strong and very very clear reception capability. Can you help me in this regard ?

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