06-26-2013, 07:49 AM
Hello BrendaAnnD,
The first step of the allignment is to pull the grid cap lead off one of the tubes and inject the IF frequency from the test generator into the top of the tube. Then the IF cap is adjusted for peak. Would you be interested in trying one of yours at 460 KHZ then again at 230KHZ and see what you get? I did get a peak at 460 but is was very weak compared to what I got at 230. What let to this entire quandry is that I swept the tank circuits before I powered it up. I injected a signal across the LC tank through a 10k resistor. The freq counter was on the signal generator side of the resistor and the o-scope was on the tank side. This is the classic way to measure resonance of a tank circuit. As I swept through resonance the amplitude of the signal on the o-scope would peak. With the 10k resistor the peak is unmistakable. With the trimmer cap all the way open (minimum value/maximum frequency) the resonant frequenct was only about 300 khz. About the mid range of the cap adjustment is 230khz. The cap appears to be fine and failing in a way that increases capacity puzzles me.
So, the components I tested seem fine, the dial is spot on, it works great, and the IF is tuned to 230 KHZ when the documentation says 460 khz. An IF frequency of 230 khz is not out of line for the period. It is possible to allign the radio with the signal generator set at 460 as the tank has a weak peak at the second harmonic. While I am fairly confident in my technical ability and testing methods, I am not past missing the obvious.
keithw
The first step of the allignment is to pull the grid cap lead off one of the tubes and inject the IF frequency from the test generator into the top of the tube. Then the IF cap is adjusted for peak. Would you be interested in trying one of yours at 460 KHZ then again at 230KHZ and see what you get? I did get a peak at 460 but is was very weak compared to what I got at 230. What let to this entire quandry is that I swept the tank circuits before I powered it up. I injected a signal across the LC tank through a 10k resistor. The freq counter was on the signal generator side of the resistor and the o-scope was on the tank side. This is the classic way to measure resonance of a tank circuit. As I swept through resonance the amplitude of the signal on the o-scope would peak. With the 10k resistor the peak is unmistakable. With the trimmer cap all the way open (minimum value/maximum frequency) the resonant frequenct was only about 300 khz. About the mid range of the cap adjustment is 230khz. The cap appears to be fine and failing in a way that increases capacity puzzles me.
So, the components I tested seem fine, the dial is spot on, it works great, and the IF is tuned to 230 KHZ when the documentation says 460 khz. An IF frequency of 230 khz is not out of line for the period. It is possible to allign the radio with the signal generator set at 460 as the tank has a weak peak at the second harmonic. While I am fairly confident in my technical ability and testing methods, I am not past missing the obvious.
keithw
