Radio Receiver Valves “REMA 2072” From The 50’S Past Century
About a month ago a friend and client of mine came to my workshop with an old REMA 2072 valve, German stereo and manufactured by 10 valves, EZ81, 2xEL84, 2xECC83, 2xEM84, EAF801, ECH81 and ECC85. Already on the bench for the first test, only the filaments remained warm, but no sound. The 30-year-old equipment stopped in a corner of the house was so dusty that it did not recognize the components on the board.
Receiver seen from behind
I proceeded with the cleaning work, verifying that some tracks of the printed circuit of the amplification section and the intermediate frequency were spent and interrupted. I plugged in again and continued speechless. I noticed that the voltage of approximately 350VDC at the “cathode” output of the EZ81 rectifier valve was present.
The cause was the R159 divider/reducer resistor of 250Ω, 1Watt, next to the main 50mF filter capacitor that was open and responsible for supplying the 230 Volts, 45mA voltage to the auxiliary grids and plates of all valves except the of the EL84 that receive slightly higher voltage.
Once these defects have been corrected and the R119 of 1M polarization of the g1 (control grid) of the ECC83 driver and the 270Ω R136 in parallel with the C151 of 100mF of the cathode of the right channel EL84 output valve, responsible for audio response curve, the amplifier returned to work, but no radio signals.
With the correction done in the printed circuit and the exchange of some components in the steps of F.I., I made the realignment of this with the RF Generator calibrated in 10.7 Mhz and 460 Khz, modulated at 1,000 Hz, respectively.
In post-F.I. is 455 Khz.
With this procedure the F.I. worked and the signals on the two channel speakers were satisfactory. The signal level was evaluated through the “magic eye” of the EM84 valve, in addition to an analog multimeter connected in parallel with one of the loudspeakers.
I captured some stations in SW and MW, after having also corrected the interruption in the coils of the resonant circuits of the antenna input with the completion of the readjustment of the pre-tuning capacitors.
Finally, I installed a new quadrant wire for the Short Wave bands because the former was fragmented.
I added a 0.047mF / 400 Volt polyester capacitor in parallel with the main power switch in order to reduce the “tic-tac” noise caused by opening and closing it.
I added two more polyester capacitors, one of 2,200 pF and another of 4,700pF, both of 400 VAC in parallel with the filter network of the rectifier valve EZ81 for the decoupling of unwanted signals such as noise and other interferences that may arise from abroad.
The “magic eye” signal indication on the left side of the receiver to work capturing an FM station
And so I finished this technical task that came to my workshop on May 26 and came out on June 11 of the current.
This article was prepared for you by Manuel Loto, native of the city of Praia, capital of the Cape Verde Islands, West Africa. Electronics Technician with more than 30 years of experience. Worked with FM and AM transmitters, communications equipment and air navigation. Specializing in Digital Electronics and he also restore old, vintage, transistorized radios, valve radios and power amplifiers.
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Note: You can check out his previous repair article below:
https://jestineyong.com/sony-receiver-sq-r-6650-repair/
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Andrew F. ali
June 25, 2018 at 10:59 pm
Very good work. Impressive. I have stopped working on valve equipment as I cannot source Thermionic valves any more. I like to read about work with valves as I reminisce the good old days where voltage was everything.
Parasuraman
June 25, 2018 at 11:17 pm
Very glad to see an article on valve radio servicing, which is my most favorite line! Very useful info shared too! You know the heart of this set, it's very clear!
Mihai
June 26, 2018 at 12:43 am
Good job Manuel ! Thank's for sharing your experience.
Albert
June 26, 2018 at 10:13 am
These old machines will work for many more years to come if handled with care by the right
experienced engineer. A master at work! And I never read about a quadrant wire before.
Robert Calk Jr.
June 26, 2018 at 11:46 am
Good job, Manuel. Thanks for sharing the repair.
Henrique Jorge Guimarães Ulbrich
June 28, 2018 at 6:13 am
Very good, Manuel. Since 1965 I have maintained a lot of valve radios, so your work pleased me a lot. Two doubts: 1) I´ve never heard about quadrant wire. What is this? 2) In the title you say it´s an old 50´s radio from the past century. However, in the first paragraph you say it´s a 30 year old radio. What is the actual age of the radio receiver? Anyhow, obrigado por compartilhar (thanks for sharing)
James
June 28, 2018 at 5:27 pm
Amazing'' 🙂
Rui Marreiros
October 22, 2018 at 12:44 am
Hello Manuel,
Your article is great.
I am currently repairing two radio valves: grundig 5399 and grundig 300. I will make some improvements, put bluetooth and external connection.
I'm thinking of getting a 2072 rook, which is also broken. has broken glass.
I am passionate about this type of radio and I have some knowledge of electronics, although little experience in FM and AM. If I need anything, can I contact you?
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Olá Manuel,
o seu artigo é excelente.
Estou neste momento a reparar dois radio a válvulas: grundig 5399 e grundig 300. Irei fazer algumas melhorias, colocar bluetooth e ligação externa.
Estou a pensar adquirir um rema 2072, que também está avariado. tem o vidro partido.
Sou apaixonado por este tipo de radio e tenho alguns conhecimentos de electrónica, embora pouca experiência em FM e AM. Se precisar de alguma coisa posso contacta-lo?
sam
November 19, 2018 at 11:48 pm
good work