09-10-2009, 03:29 PM
If the 39-25 buttons work the same as the 40-150, then this is how it works.
Inside the chassis, there should be a mechanical switch assembly block that is actuated by the push buttons, maybe 4 or 5 inches long and an inch or so wide, pretty much in the middle of the chassis. Bolted to the back of the chassis is a second assembly that holds coils and compensators. The two assemblies are connected by fabric covered wires and braid.
For normal dial tuning, the tuning condenser has two separate sets of plates that move together in a gang. One is for tuning the oscillator frequency, and the other is for tuning the frequency of the antenna circuit. When you select the "Dial" button, the gang condenser (and associated coil) is in the circuit and you tune with the tuning knob.
If you select any of the other buttons, you cut the gang condenser and coil(s) out of the circuit and substitute a manual tuning coil with a movable slug for the oscillator and a manual compensator (adjustable mica cap) for the antenna. Each push button selects a different pair of these. For tuning the push buttons, you access the coils and compensators from the back of the chassis.
In addition to these adjustable components, there are some fixed mica condensers that are used because they are stable with temperature. As long as they are in spec, and they usually are, you don't need to worry about them.
Each push button coil and compensator has a limited tuning range. The ones on the right as you face the back of the chassis are for the lower part of the AM band. The frequency range of each push button is probably etched on the back of the chassis, but it will certainly be part of the service data.
For tuning, you push in a button (except the "Dial" button), and then find the corresponding coil and compensator. Try moving the coil slug first. Usually, you zero in on a station with the coil, and then adjust the antenna compensator for greatest volume. Then you go back and forth a few times to make sure you have both adjusted optimally.
Good luck.
Inside the chassis, there should be a mechanical switch assembly block that is actuated by the push buttons, maybe 4 or 5 inches long and an inch or so wide, pretty much in the middle of the chassis. Bolted to the back of the chassis is a second assembly that holds coils and compensators. The two assemblies are connected by fabric covered wires and braid.
For normal dial tuning, the tuning condenser has two separate sets of plates that move together in a gang. One is for tuning the oscillator frequency, and the other is for tuning the frequency of the antenna circuit. When you select the "Dial" button, the gang condenser (and associated coil) is in the circuit and you tune with the tuning knob.
If you select any of the other buttons, you cut the gang condenser and coil(s) out of the circuit and substitute a manual tuning coil with a movable slug for the oscillator and a manual compensator (adjustable mica cap) for the antenna. Each push button selects a different pair of these. For tuning the push buttons, you access the coils and compensators from the back of the chassis.
In addition to these adjustable components, there are some fixed mica condensers that are used because they are stable with temperature. As long as they are in spec, and they usually are, you don't need to worry about them.
Each push button coil and compensator has a limited tuning range. The ones on the right as you face the back of the chassis are for the lower part of the AM band. The frequency range of each push button is probably etched on the back of the chassis, but it will certainly be part of the service data.
For tuning, you push in a button (except the "Dial" button), and then find the corresponding coil and compensator. Try moving the coil slug first. Usually, you zero in on a station with the coil, and then adjust the antenna compensator for greatest volume. Then you go back and forth a few times to make sure you have both adjusted optimally.
Good luck.
John Honeycutt
