01-03-2022, 08:56 PM
The FM module has been mounted to the front wall of the chassis. All connections have been made, I used small shielded cable for the audio.
[Image: https://live.staticflickr.com/65535/5179...b60d_c.jpg]Adding FM to a Philco 118 by Steve Davis, on Flickr
The module requires 6.3 to 16 volts AC or DC with one side grounded to the chassis. The Philco 118 uses 6.3 volt tubes but, the 6.3 volt winding has a grounded center tap. This is a problem. One half of the winding could be used with a voltage doubler circuit. I looked all through my "someday kit" and could not find a suitable capacitor to make the doubler. But, I did find about a half a dozen of these nice little 12 volt, 150ma transformers, so I decided to go with one of them.
[Image: https://live.staticflickr.com/65535/5179...a7f8_c.jpg]Adding FM to a Philco 118 by Steve Davis, on Flickr
The open circuit voltage of the transformer is 16 volts, right at the high limit of the module. With a 150ma transformer and only a 24ma draw from the module, my fear is, the voltage might not come down much from the 16 volts. I decided to remove a few turns from the secondary winding. I disassembled the transformer and unwound 80 turns then reassembled the transformer. The OC came down to 10 volts, good enough.
[Image: https://live.staticflickr.com/65535/5179...77f8_c.jpg]Adding FM to a Philco 118 by Steve Davis, on Flickr
[Image: https://live.staticflickr.com/65535/5179...b60d_c.jpg]Adding FM to a Philco 118 by Steve Davis, on Flickr
The module requires 6.3 to 16 volts AC or DC with one side grounded to the chassis. The Philco 118 uses 6.3 volt tubes but, the 6.3 volt winding has a grounded center tap. This is a problem. One half of the winding could be used with a voltage doubler circuit. I looked all through my "someday kit" and could not find a suitable capacitor to make the doubler. But, I did find about a half a dozen of these nice little 12 volt, 150ma transformers, so I decided to go with one of them.
[Image: https://live.staticflickr.com/65535/5179...a7f8_c.jpg]Adding FM to a Philco 118 by Steve Davis, on Flickr
The open circuit voltage of the transformer is 16 volts, right at the high limit of the module. With a 150ma transformer and only a 24ma draw from the module, my fear is, the voltage might not come down much from the 16 volts. I decided to remove a few turns from the secondary winding. I disassembled the transformer and unwound 80 turns then reassembled the transformer. The OC came down to 10 volts, good enough.
[Image: https://live.staticflickr.com/65535/5179...77f8_c.jpg]Adding FM to a Philco 118 by Steve Davis, on Flickr
M R Radios C M Tubes
