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BX765X & BX665X

Geschreven door PANDU RAJAN op 11. Feb 2004 18:46:13:

1. Recently I have been able to restore the radio sets BX765X (1948) & BX665X (1947) into satisfactory operation. In the set BX765X they have used a Dual volume control but both the volume controls are connected in series i.e. the variable output of the 1st volume control is connected to the top of the 2nd volume control and the variable output of the 2nd volume control goes to the input of the L.F. amplifier ECH21.Now I face a peculiar problem in the set BX765X. For increase in volume control from 0 to Approx. 50% the sound output is less. When it is increased more than 50% then a good sound output is obtained. In the case of a set with single type of volume control as is in BX665X this type of problem is not there. I have checked the Volume control and it is O.K. My question is that “ Is this type of problem there in all the models of BX765X”?

2. Philips have used in many of their sets the valves ECH21 or EF22 as the L.F. audio preamplifier. Can the same be done with ECH81 or EF89 also?

3. In BX765X Philips have used EF22 as the I.F. amplifier where as in BX665X they have used ECH21 as the I.F. amplifier and the triode part of ECH21 has been used as the L.F. audio preamplifier. Can the EF22 of BX765X be replaced with ECH21 and the triode part of the ECH21 be used as additional audio preamplifier to get better sound output at lower volume control positions? What modification can be done? Can anybody suggest?


PANDU RAJAN
pandurajan@rediffmail.com





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