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Here's a general purpose AM alignment procedure that I use on pretty much every radio over the last 50 years; rarely do I use printed procedures. Some will find fault with some of the steps but there are reasons for everything here. There shouldn't be any gross errors but sometimes it's hard to correct one's own writing.
Generic AM Radio Alignment for Pre-War Models
IF ADJUSTMENT
1. Look at the schematic and find the IF frequency. It will be between 130 and 475KHz for most pre-1945 radios.
2. Turn the radio on; set your radio to the low end of the Broadcast Band (usually around 535KHz, it’s not critical). Set volume to maximum.
3. If there is a ground post on the signal generator, connect a wire from it to a secure connection on the radio chassis.
4. Connect your signal generator to the antenna post and ground. This is usually done with coaxial cable but plain wire can be used for this adjustment.
5. Set the signal generator to the IF frequency with modulation (around 70% is best but not critical; that’s usually around 75% rotation of the modulation knob). This IF frequency is critical; measure it with a freq counter and NO modulation. DO NOT RELY ON A SIGNAL GENERATOR DIAL FOR ACCURACY!
6. Adjust the output level of the signal generator so that you can just hear the modulating tone (usually 400 to 1000Hz, not critical).
7. Adjust the IF can(s) for maximum audio while always reducing the signal level to the lowest audible tone. TUBE SHIELDS MUST BE ON. If an adjustment causes a sudden squeal, back off the adjustment as little as possible until the squeal stops. At times there will be high voltage on the adjustment screws so it is wise to wrap tape around your adjustment tool shaft.
8. The If is now completed
RF ADJUSTMENT
1. Connect the signal generator to the antenna post through a 300-400 ohm resistor (not critical) and ground.
2. Set the radio to the Broadcast Band, high end of the dial. Note the highest numbered frequency on the dial (usually around 1600KHz). Now set the radio to the next lower numbered frequency (1500 or 1400KHz usually). If there aren’t many numbered points, choose a frequency that is closest to ½ inch down the dial from the highest mark.
3. Set your signal generator to the freq determined in the above step (1500 or 1400 usually) with modulation control set to about 75% of maximum. (very roughly 70% modulation)
4. Locate the Oscillator trimmer cap; it is often located on top of the tuning cap. If you are not sure which one it is, don’t worry, you will find it easily. It will be the only trimmer to move the dial frequency); as you proceed, you will be correcting any mis-adjustments.
5. Tune the radio in the area of the input signal (1500, 1400); with luck you will hear the signal somewhere near where it should be. If you don’t hear it with an increased signal generator output, you most likely have a problem.
6. If you do hear the injected signal generator tone, notice if it is above or below where it should be. If it is above (1500, 1400), turn the trimmer counter-clockwise; if it is below, turn the trimmer in or clockwise until the dial is accurate at this point.
7. Set the radio and signal generator to 600KHz. With luck they should be very close. If your radio is equipped with a “padder” adjustment cap (usually located on the chassis), adjust it until you hear the tone at 600KHz. If you do not have a “padder”, you can loosen the screws behind the dial and move the dial until you hear the signal at 600KHz. If you do slip the dial, you must go back and repeat steps 5 and 6.
8. Set the radio to the highest marked dial frequency on the Broadcast Band (1600 or 1500 usually). Set your signal generator to the same frequency with the usual modulation.
9. Find the tone by tuning your radio dial; it should be fairly accurate but if it isn’t, there’s probably not a lot you can do to make it perfect. Adjust the BC trimmer for maximum audio with minimum signal generator output level (don’t lower the modulation). If you have a three section tuning cap, you will have two trimmers; the additional trimmer is for “antenna” and is typically a very broad adjustment. At times you will run out of adjustment on the antenna trimmer but don’t worry about it if you do. On the higher-end radios, trimmers are often located in rows on the bottom of the chassis; on these radios the “padder” (600KHz adjustment) is located near the trimmers but located separately.
10. If you have shortwave bands, repeat steps 8 and 9 while in those bands but choosing a marked dial frequency roughly above the 1600/1500 marks on the dial. There are no “Padders” on shortwave bands.
11. Remove the resistor from the antenna post and connect your antenna. Enjoy your radio.
Pete AI2V
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