01-29-2014, 09:31 AM
If you aren't receiving anything on the low end of the band it could be something that keeps the oscillator from working below a certain frequency. As long as you get stations (or the sig gen tone) at the upper part of the band, we know that your IF and audio sections are working. They should not be affected by the dial setting.
There is an easy way to test the oscillator, using a second radio. Set a known good radio near your 40-155, a foot or so apart. Set the 40-155 at a station you know you can receive, as low a frequency as possible. Then set the "known good" radio dial to 455 KHz above the frequency of the 40-155 and tune around there up and down a bit, slowly and carefully.
You should hear the good radio howl when the two radios are 455 KHz apart. This shows your local oscillator is working at this frequency. You might have to turn the volume down on the 40-155 and up on the good radio to hear better.
If your good radio is digital, just set it 450 above the station frequency and tune the 40-155 around a bit. It doesn't have to be on the station for this test to work, as long as your oscillator is working and the radios are 455 KHz apart.
Now, do the same thing at a frequency below where your 40-155 can receive stations (or sig gen tone), and maybe several other places low on the dial. If you hear the howl, then your oscillator is working and we go back to scratching our heads. If you don't hear the howl, then your oscillator isn't working at those frequencies, and we can try to figure out why.
If you have a spare mixer tube (detector/oscillator) try swapping them out and see what happens. If nothing changes, we have to try something else.
There is an easy way to test the oscillator, using a second radio. Set a known good radio near your 40-155, a foot or so apart. Set the 40-155 at a station you know you can receive, as low a frequency as possible. Then set the "known good" radio dial to 455 KHz above the frequency of the 40-155 and tune around there up and down a bit, slowly and carefully.
You should hear the good radio howl when the two radios are 455 KHz apart. This shows your local oscillator is working at this frequency. You might have to turn the volume down on the 40-155 and up on the good radio to hear better.
If your good radio is digital, just set it 450 above the station frequency and tune the 40-155 around a bit. It doesn't have to be on the station for this test to work, as long as your oscillator is working and the radios are 455 KHz apart.
Now, do the same thing at a frequency below where your 40-155 can receive stations (or sig gen tone), and maybe several other places low on the dial. If you hear the howl, then your oscillator is working and we go back to scratching our heads. If you don't hear the howl, then your oscillator isn't working at those frequencies, and we can try to figure out why.
If you have a spare mixer tube (detector/oscillator) try swapping them out and see what happens. If nothing changes, we have to try something else.
John Honeycutt
