BX798X-02 (Algemeen)

door Pandu Rajan , 15.04.2009, 15:56 (5704 dagen geleden)

Dear Forum Members.

I am in the process of restoration of the above 1949 radio set. The restoration of the chasis is nearly complete. The audio part was in a mess and after restoration it is working O.K. But I have certain doubts. The schematic is nearly identical to BX806X. The preamplifier is EF40 and the phase inverter is ECC40. The output valve is 2 X EL41. ECC40 has been used as a cathode follower. As per the service manual the voltage at the two anodes of the valve ECC40 should be around 98 Volts. But in the above radio set the voltage comes to 145 Volt on pin no 2 and 150 volt at pin no 5 of ECC40. The voltage tap of the incoming voltage is at 220 Volt. The voltage at the grid pin no 3 is 71 Volt and pin no 6 is 91 volt. As per the service manual the cathode voltage should be 83 volt but I am getting 94 volt. the voltage between cathode and the two grids is aprrox. -1.73 volt each. I am unable to understand why I am unable to get the correct anode voltages? Why the anode voltage is high? I have checked the following components and they are O.K.
1.R64 and R65 - 100K Ohm
2.R63-1.2M Ohm
3.R60- 68K Ohm.
4.R62 0.18M Ohm
5.C97 - 0.1uf
6.R58- 1M ohm
7.R59-47K Ohm
The audio portion is working O.K.

Can someone guide me?

Regards

P.Rajan