17-05-2017, 09:47 AM
Reference to the attached circuit diagram of the output stage of the VHF64.
It's possible that the components R40 and C70 form a hum cancelling circuit. A small amount of 100Hz ripple is fed back to the cathode of the EL84. Because of the presence of the cathode bypass capacitor and the values of the feedback resistor and capacitor the amount of feedback will be very small. The reactance of the cathode bypass capacitor C69 at 100Hz is 31ohms and the 0.2mfd feedback capacitor C70 is 8000ohms.
Geordie McBoyne.
It's possible that the components R40 and C70 form a hum cancelling circuit. A small amount of 100Hz ripple is fed back to the cathode of the EL84. Because of the presence of the cathode bypass capacitor and the values of the feedback resistor and capacitor the amount of feedback will be very small. The reactance of the cathode bypass capacitor C69 at 100Hz is 31ohms and the 0.2mfd feedback capacitor C70 is 8000ohms.
Geordie McBoyne.
