It is not because CR769 doesn't do its job but voltage never goes below 10V so that it can conduct. In your web page WF4 shows CR769 cathode doesn't go below 65V. Just to make sure: Are +120V UNREG and +30V UNREG OK (I am using 606 schematic, not 606A in case names are different)? Is there a 606A service manual? Once you fix the DC restorer you can correct the voltages. You can try turning down the -5500V supply to see if it gives you longer time to work on the HV supply. Your DC restorer could be the cause, may be the tube is drawing too much current. It is quite possible that HV supply is working harder than expected because of some fault/load in high voltage side.
bad/heating transformer: I think you eliminated it by heating/cooling the transformer. Pin3 is connected to voltage divider of R734A and R734B, without -5500V pin 3 voltage range you see looks reasonable. R736 provides +15V to +10.99 depending on its position (ignore the loading of R734A. The OpAmp removed, the circuit does NOT oscillate Without opamp there is no base drive to start the oscillations.Īnd the voltage at pin 3 is between 11 and 15V, dependent on R736.When the circuit is not oscillating there is no -5500V to pull R734B to -5500V. Voltage coming from R730 and -5500V should balance each other to ~ zero volts by the ratio of R734A and R734B. At nominal output voltage of -0.5V, pin 3 voltage would be at -0.05V. For all practical purposes you can assume U740 is trying to drive pin 3 to close to zero volt because of this large gain from pin3 to output. WithAmplification factor is (100k+12k)/12k = 9.33 based on the schematic on your web page. It'sĬonfigured as a non-inverting amplifier with a 1.83 amplification factor. I don't quite understand how U740 (LM741 OpAmp) works here. What would be the best way to remove the HV feedback loop from the circuit (asĪ test)?Feedback loop is needed for proper base bias of Q714.
I don't have a good theory but I can help explaining the HV loop. First of all very nice description of the problems in your web page, very useful for others to understand what is happening.
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