28-01-2014, 10:54 AM
Typical current draw for the UCL11 (output section) = 36 ma at a Vg of - 6 volts.
The current draw of the loudspeaker field coil will be around 15 ma so the overall current draw of the receiver should be somewhere around 60/65 ma.
Bias for the output valve is developed across the tapped 100 ohm resistor so if receiver current draw is 60 ma then voltage drop across that resistor will be 6v which is correct for the output valve bias voltage.
If fitting a silicon rectifier to replace the original selenium then as a ball park figure assume that the selenium rectifier had a forward voltage drop of around 30 volts, if that was the case then that would suggest that the series resistor for the silicon rectifier needs to be somewhere around 500 ohms.
If you want to run the receiver at 240 volts ac the I would suggest increasing the value of the rectifier series resistor and also fit a series resistor in the heater chain to drop 20 volts at 100 ma.
Lawrence.
The current draw of the loudspeaker field coil will be around 15 ma so the overall current draw of the receiver should be somewhere around 60/65 ma.
Bias for the output valve is developed across the tapped 100 ohm resistor so if receiver current draw is 60 ma then voltage drop across that resistor will be 6v which is correct for the output valve bias voltage.
If fitting a silicon rectifier to replace the original selenium then as a ball park figure assume that the selenium rectifier had a forward voltage drop of around 30 volts, if that was the case then that would suggest that the series resistor for the silicon rectifier needs to be somewhere around 500 ohms.
If you want to run the receiver at 240 volts ac the I would suggest increasing the value of the rectifier series resistor and also fit a series resistor in the heater chain to drop 20 volts at 100 ma.
Lawrence.
