03-03-2023, 11:42 AM
Last night the broken CCH35 valve was replaced, the wiring around the mains transformer checked. Surprisingly, the single pole on-off switch is OK, contact resistance 0.3ohms.
Connect up to the variac, supply the chassis with 100volts. After several minutes a loud hum coming from the 'speaker, 'scope connected to the reservoir capacitor. All too evident the smoothing capacitor is useless. Original is 16 + 32mfd, found a good 32 + 32mfd capacitor which should be OK to use in this receiver. The Mullard Maintenance Manual tells us that the CY31 rectifier's HT reservoir capacitor can be 32mfd when used with a 150ohm series anode resistor, which it is.
The attachment shows the waveform across the reservoir capacitor.
Geordie McBoyne.
Connect up to the variac, supply the chassis with 100volts. After several minutes a loud hum coming from the 'speaker, 'scope connected to the reservoir capacitor. All too evident the smoothing capacitor is useless. Original is 16 + 32mfd, found a good 32 + 32mfd capacitor which should be OK to use in this receiver. The Mullard Maintenance Manual tells us that the CY31 rectifier's HT reservoir capacitor can be 32mfd when used with a 150ohm series anode resistor, which it is.
The attachment shows the waveform across the reservoir capacitor.
Geordie McBoyne.
