How to Add an Aux Input to a Tube Radio
By Simon Foden
Tube technology was superseded by transistor technology in the 1950s. Transistors are more reliable for most applications. But many people prefer the sound of tube amplification. If you've got a vintage tube radio for this reason, you may enjoy the warm and bright tone of the tubes. If your tube radio is not fitted with an auxiliary input, you can add one yourself in order to feed high-tech audio through the tubes.
Unplug and dismantle your radio. Unscrew the back panel to expose the wiring and circuit assembly.
Clean the tip of your soldering iron with a wet sponge. Dry with a dry, cotton cloth. Turn the iron on so that it is ready for use.
Locate the tubes in the signal chain. "Signal chain" is a term that describes the sequence of components in an audio device. Start at the power supply and follow the sequence of components until you reach the tubes. The tubes are the glass cylinders plugged into the inside of the amplifier. Put an a pair of latex gloves and remove all of the vacuum tubes. It's a good idea to remove the tubes while you are performing modifications, because they can shatter if accidentally banged or jolted.
Break the connection between the antenna input and the circuit board. If this is a wire connection, snip the wire in the middle. If it is a solder joint, melt the joint with a clean soldering iron. Press the soldering iron tip gently over the solder joint until smoke rises from it and gently pull the antenna input connector away from the board.
Take the auxiliary socket assembly from the pack. Strip the end of the ground wire (black wire) connected to the auxiliary socket so that wire is exposed. Disconnect the radio ground wire and strip the end. Solder that metal end of the ground wire to the ground wire running from the power supply of the radio. Dip the soldering iron tip in solder and gently press against the wire and onto the circuit board. If you have a particularly old tube radio, the circuit may be mounted on a brass heat-spreader board. If it is, twist the exposed wires around each other and solder them onto the heat-spreader board.
Strip the end of the power wire (red) connected to the auxiliary socket. Solder it to the power supply output terminal located on the side of the power supply, below the female socket, facing toward the circuit board.
Strip the end of the auxiliary socket emote wire (yellow) and solder it to the first tube socket along, after the power transformer. The tube socket is the plastic housing that you removed the tube from. It is typically screwed into the chassis of the radio. This sends the aux signal through the radio's amplification circuit.
Drill a hole in the front of the radio chassis, large enough for the aux input socket to poke through. Use a standard electric drill and 0.0984-inch drill bit. Remove the jack-mounting plate and screws from the pack. Screw the jack-mounting hardware onto the inside of the chassis and mount the jack. The mounting hardware enables you to fasten the jack to the inside of the radio.
Simon Foden has been a freelance writer and editor since 1999. He began his writing career after graduating with a Bachelors of Arts degree in music from Salford University. He has contributed to and written for various magazines including "K9 Magazine" and "Pet Friendly Magazine." He has also written for Dogmagazine.net.