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Restoring Antique Valve Amplifier Ahuja TM-50

By on February 11, 2020
antiques amplifier repair

 

 

 

 

 

 

 

 

 

 

 

 

 

This Ahuja Valve Amp was gifted to me by one of my friends, looking at my interest in collecting antique pieces. It was lying in one corner for many years without even opening. Though many customers asked whether I could restore it and give it, I was turning them away. However, having reached almost 70 years, and as there is none in my house who will take over or continue this work, I decided to do some ‘load-shedding!’

how to fix and repair antiques amplifier

So, when one of my regular customers, who has bought a few items in the past, was repeatedly asking for it, I decided to open it and see the condition. I cleaned the set thoroughly. In all such restorations, it is mandatory to check and replace the Tank Capacitor, which I did and ensured that the power supply was safe enough to switch on. Found a couple of Valves missing. Mains On/Off switch was defective. Replaced the switch and looking at the bottom circuit, assumed what could be the valve number and placed two EL84 Valves. Switched on and it was showing life. But another ECC83 had a crack on it.

Replaced that also and I got a hopeful output now. So, combed the bottom of the Amp for defective components. Replaced rest of the electrolytic capacitors, one open resistor and one potentiometer which was found defective. Provided a missing knob, and a new mains cord in place of a half cut. The set had a nice lay-out and arrangement of components. The (-) points of Electrolytic Capacitors were all uniformly arranged on one side! The trouble shooting was very, very easy! This shows the class of the Manufacturer and how principled they were! Cleaned and lubricated all the controls and valve bases.

antique amplifier repair

Switched on the set and it was working with superb output! Though I also replaced input of Mic-3 with the latest RC socket, I forgot to click when all work was finished! So excited was I! (In mono sets, whenever I provide a new input, I give one each for Left and Right channel, interconnecting these with a 0.1/400V polyester cap.) In fact, I was a bit reluctant to part with the set, but forced myself to give it off, as a part of my commitment and maintaining credibility!

how to fix antiques amplifier

This job was more than ready to jump into the satisfaction bag, and I gladly let it do!

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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You may check on his previous repair article below:

https://jestineyong.com/escaped-from-a-potential-fire-hazard-in-lg-crt-tv/

 

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21 Comments

  1. Albert van Bemmelen

    February 11, 2020 at 3:48 pm

    It is always a good feeling having saved a device that was made with care in those days. Although I haven't done much with those valves or units with radio tubes from the past, I am familiar with the famous EL-84 amplifier end stage valves. Being just over 60 I once found a very old defect AM receiver that didn't even have real permanent magnets in the very old loudspeaker. Instead it used an electromagnet being the coil that was attached to the rimple surpressor in the rectified DC power supply of the unit. Although probably those old devices are the only ones that will survive an EMP burst from a nuclear explosion (hope they will never happen ever!) it is nice that our computers are no longer build with those ancient large much energy consuming components. And our worldfamous firm ASML in Eindhoven will make incredible smaller revolutionary new miniature circuits possible. Sadly the USA is not allowing them selling that state of the art technology to countries like China.

    Likes(3)Dislikes(0)
    • Parasuraman S

      February 11, 2020 at 6:48 pm

      Many thanks for a detailed response! Good to refresh the history of events connected with! Nice to know these!

      Likes(4)Dislikes(0)
  2. Mark

    February 12, 2020 at 6:16 am

    Hey Parasuraman,
    Yet another fantastic repair.
    I haven't had much to do with valve circuitry, but am always interested in learning new things - even if they are old!
    Keep up the good work and sharing so that we can all learn from one another 🙂

    Likes(3)Dislikes(0)
    • Parasuraman S

      February 12, 2020 at 11:08 pm

      Many thanks for your encouraging comments, always serving as a fuel to proper forward!

      Likes(0)Dislikes(0)
  3. Yogesh Panchal

    February 12, 2020 at 4:49 pm

    Salute! Antique Specialist.

    Likes(1)Dislikes(0)
    • Parasuraman S

      February 13, 2020 at 8:49 pm

      Many thanks, Panchal!

      Likes(0)Dislikes(0)
  4. Imoudu Onwumah

    February 13, 2020 at 5:11 am

    Sir,

    I come across one of your articles on crt tv repair and how you use universal power module on the board. You said you have explained the use of it before. I am new to Jestine blog.So,can you link me to
    that article so as to learn from it? Please help.

    Likes(1)Dislikes(0)
    • Parasuraman S

      February 13, 2020 at 8:48 pm

      If you are using a three pin module, it will have red, black and green wires. Just ignore the green wire and tie it safe, with a tape so that it does not make accidental contact. Remove the STR, PWM IC and Mosfet etc. from the primary switching side. Connect the Red wire to the return of B+ that comes out from the primary side of SMPS Transformer. Connect the black to the hot ground (Primary side). There is a pot in the module. adjust it to the minimum. Remove the jumper or low ohm resistor that goes to primary of LOT (FBT) and connect a 100W Bulb as load there. Switch on and adjust the pot in the module to get the desired voltage. Do it slowly and very carefully as you are in the high voltage, high current primary of the SMPS. Please take all precaution necessary in handling high voltage areas of SMPS. If you are not familiar, just ignore this, as any mistake there might give a lethal shock. So, please take adequate precautions.

      Likes(2)Dislikes(0)
  5. Robert Calk Jr.

    February 13, 2020 at 8:27 am

    Good job, Parasuraman!

    Likes(1)Dislikes(0)
    • Parasuraman S

      February 13, 2020 at 8:41 pm

      Many thanks!

      Likes(0)Dislikes(0)
  6. Waleed Rishmawi

    February 13, 2020 at 6:02 pm

    a job well done my friend. I enjoyed your articles and your professional repair and replacing component and the result was superb. keep up the good work and have a blessed day

    Likes(1)Dislikes(1)
    • Parasuraman S

      February 13, 2020 at 8:40 pm

      Many thanks for your encouraging words! It gives a boost!

      Likes(0)Dislikes(0)
  7. Humberto.

    February 15, 2020 at 3:40 pm

    Well-done, Parasuraman.

    Likes(1)Dislikes(0)
    • Parasuraman S

      February 17, 2020 at 6:07 pm

      Many thanks, Humberto!

      Likes(0)Dislikes(0)
  8. jai

    February 16, 2020 at 10:51 am

    Good job Parasuraman

    Likes(1)Dislikes(0)
    • Parasuraman S

      February 17, 2020 at 6:07 pm

      Many thanks, Jai

      Likes(0)Dislikes(0)
  9. Reuben Sylvester

    March 5, 2020 at 1:15 pm

    Hello Sir, i am a regular follower of your repair adventures. I recently got this very same amplifier and would like to fix it. My father had an amplifier circuits book featuring amplifier circuits of all the old-time Indian PA amplifiers but that book is long lost. I am on the look out for the circuit diagram of this amplifier (output is 4 x EL84). Can you guide me on where I can obtain the circuit schematic from? Thanks and regards, Reuben

    Likes(1)Dislikes(0)
    • Parasuraman S

      April 6, 2020 at 8:27 am

      I have no idea where you are located. I suggest you comb the web and you will find many circuit diagrams in antique reworking shops, especially in UK and Australia.

      Likes(0)Dislikes(0)
      • Reuben Sylvester

        May 2, 2020 at 10:08 pm

        I am located in Trivandrum, Kerala. Any guidance in relation to the circuit of this amp, would be really helpful. Thanks and Regards.

        Likes(0)Dislikes(0)
  10. New man

    June 7, 2020 at 1:23 am

    Respected sir ,
    Your hard working,and success are
    Excellent !
    Congratulations !

    Likes(1)Dislikes(0)
    • Parasuraman S

      June 13, 2020 at 11:41 pm

      Many thanks for your support!

      Likes(0)Dislikes(0)

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