01-24-2013, 08:07 PM
OK, allow me to clarify things a bit.
The dial lamp is attached to a movable bracket which slides left or right on top of the dial scale. It is brought into position above one of the eight scales, depending upon the position of the band switch.
These photos may help to illustrate:
[Image: http://www.philcoradio.com/images/phorum..._00001.jpg]
Band switch in AM (Broadcast) position
[Image: http://www.philcoradio.com/images/phorum..._00002.jpg]
Band switch in band 5 position (25 meters)
The lamp must be a miniature size lamp due to the limitations of space. A C7 candelabra will not physically fit.
Now, about the Candohm. It is a two section resistor, 28 ohms (I erroneously stated 22 ohms earlier, I have since corrected that post) and 1020 ohms. The 28 ohm section serves as a dropping resistor for the filament string. The "hot" side of the AC line connects to the junction of the 28 and 1020 ohm sections. At the other end of the 1020 ohm section, originally, was the 14 volt dial lamp; the other side of which connected to the "neutral" side of the AC line. In other words, the 1020 ohm section was in series with the dial lamp.
One section of the Candohm is open, so it will be removed altogether.
The filament string adds up to 105 volts. Adding a 28 ohm resistor in series dropped 8.4 volts, which added to 105 equals 113.4 volts. Not enough of a drop on today's 125+ volt AC lines. A 68 ohm resistor will drop 20.4 volts, which when added to 105 equals 125.4 volts - perfect.
The other section of the Candohm dropped the AC line to allow the 14 volt pilot lamp to operate properly. But I think using a dropping resistor in this fashion is a very inefficient way to provide for a dial lamp. The 1020 ohm section wasted over 10 watts of power just to provide the proper voltage for the dial lamp.
Since the Candohm must be replaced anyway, I wanted to do away with the 1020 ohm section entirely and use a 120 volt lamp if at all possible.
LED lamps are made, with miniature bayonet bases, which can operate at 120 volts AC. An LED of this type is looking more like a good answer to this problem.
I was just thinking that I had seen somewhere how someone used an LED night light in a Philco table model which originally used one of those 4 watt 117 volt incandescent night light bulbs, and it worked out OK.
The dial lamp is attached to a movable bracket which slides left or right on top of the dial scale. It is brought into position above one of the eight scales, depending upon the position of the band switch.
These photos may help to illustrate:
[Image: http://www.philcoradio.com/images/phorum..._00001.jpg]
Band switch in AM (Broadcast) position
[Image: http://www.philcoradio.com/images/phorum..._00002.jpg]
Band switch in band 5 position (25 meters)
The lamp must be a miniature size lamp due to the limitations of space. A C7 candelabra will not physically fit.
Now, about the Candohm. It is a two section resistor, 28 ohms (I erroneously stated 22 ohms earlier, I have since corrected that post) and 1020 ohms. The 28 ohm section serves as a dropping resistor for the filament string. The "hot" side of the AC line connects to the junction of the 28 and 1020 ohm sections. At the other end of the 1020 ohm section, originally, was the 14 volt dial lamp; the other side of which connected to the "neutral" side of the AC line. In other words, the 1020 ohm section was in series with the dial lamp.
One section of the Candohm is open, so it will be removed altogether.
The filament string adds up to 105 volts. Adding a 28 ohm resistor in series dropped 8.4 volts, which added to 105 equals 113.4 volts. Not enough of a drop on today's 125+ volt AC lines. A 68 ohm resistor will drop 20.4 volts, which when added to 105 equals 125.4 volts - perfect.
The other section of the Candohm dropped the AC line to allow the 14 volt pilot lamp to operate properly. But I think using a dropping resistor in this fashion is a very inefficient way to provide for a dial lamp. The 1020 ohm section wasted over 10 watts of power just to provide the proper voltage for the dial lamp.
Since the Candohm must be replaced anyway, I wanted to do away with the 1020 ohm section entirely and use a 120 volt lamp if at all possible.
LED lamps are made, with miniature bayonet bases, which can operate at 120 volts AC. An LED of this type is looking more like a good answer to this problem.
I was just thinking that I had seen somewhere how someone used an LED night light in a Philco table model which originally used one of those 4 watt 117 volt incandescent night light bulbs, and it worked out OK.
--
Ron Ramirez
Ferdinand IN
