Rejuvenation Of PHILIPS Tuner Amplifier Model AH719
This Amp was one among the few items that I picked up from second sales done by a Technician, who lost vision and discontinued his shop. I paid him a good amount and never bargained as a help or aid and never bothered to calculate the conditions or value of these things, as he was in dare need of financial support. Well, I felt pity for him. Luckily he was settled to a certain extent and could manage with the family resources and support he got. This was lying in my workshop collecting more dust from 2016!
One of my regular customers, who was always very keen and had craze in adding antique items to his collections, was after me to get this repaired and given to him. After succumbing to his persuasive demands, recently I took it up and cleaned the set thoroughly. The tuner section was in very bad shape with a lot of transistors and diodes either open or short. I found a few such transistors and diodes in the pre-amp section too. The tank capacitor was found leaking. Almost all the fixed capacitors in the Tuner sections were cracked. The coils were open and there was no way I could restore the tuner section, as these parts were never available for replacement. I used 6800uF/80V capacitor instead of the 5000uF/50V can capacitor used in the set.
I added one Speaker protection-cum-power delay circuit using the TA7130P. I assembled the circuit on a strip board and fixed it near the heat zinc where there was enough space to accommodate it comfortably.
Then replaced all the electrolytic capacitors on the board and checked the function, wiring it to the power supply for easy checking.
I also removed one pair of output transistors, picture of which are given below for info.
As you can see from the datasheets, these are Darlington power transistors. The Amp board worked very well and I was very happy to listen to the quality of sound. So, fixed it back.
After checking it for its proper working for several hours, I closed the case and again used it for three days before giving it to the nagging buyer!
Mission accomplished and satisfaction collected as usual! I took only a marginal amount just to cover the cost of the components replaced (Equivalent to around 18-19 US$), because I never felt like making a profit on this sale, especially knowing the background of the person from whom I took it. The buyer was a worker and a deserving one too and was very happy to acquire it though he had to wait for a very, very long time. In fact, let me be very frank, I had put him to such a wait that he started imploring and I feel guilty about it now! He is after a few more sets lying with me and hope I will find time to bring them back to shape.
P.S. The defective components were bought by a technician, another crazy collector, when I published this in my group and I passed this benefit also to the buyer of the Amplifier.
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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