12-06-2008, 09:34 PM
All,
I am ready to align my Philco 70. I am getting nearby stations pretty good, but I want to properly align the receiver.
I have abbreviated the alignment instructions I got from the Riders manual below:
1) Disconnect the grid clip to the 1st detector. Connect RF signal generator clip to grid of 1st detector and the ground clip to the chassis. Adjust RF signal generator to 260 kc, and dial position on radio to 55. Adjust trimmers 1, 2 and 3, in order, to achieve maximum output signal.
2) Reconnect grid clip on 1st detector. Connect RF signal generator clip to ANT and the ground clip to chassis. Adjust generator to 1400 kc, and dial position to 140. Adjust trimmer 4 to achieve maximum output signal. There are similar instructions for trimmers 5, 6, 7, then 4 again, but that is not the issue right now.
Here's what I've done so far:
- I have an RF signal generator, and I've checked it against a digital receiver (from 530 to 1710 on the AM dial) and I am clearly getting the 400 Hz
internal tone. As I adjust the frequency on the generator, I get the maximum volume from the receiver when pointer is right on the desired frequency (at several points in the AM range), so the generator is working properly and appears to be accurate and graduated correctly.
- To measure output signal, I will hookup my DMM in parallel with the output transformer secondaries and measure VAC. That way, I can hear the speaker and see the voltage.
Here's the problem:
When I do step 1 above, I get nothing from the radio speaker at all (except static). Because the radio works, I am reluctant to give trimmer 1 too many turns ... thus far, I've been careful to keep track of the original settings. Since I cannot tune my digital receiver down to 260 kc, I can only presume that the RF signal generator is working at that frequency; however, it is on a different frequency band. The other frequency bands are working.
When I try step 2 above, I get the generator tone near 140 on the dial ... I should be able to adjust trimmers 4 - 7 without too much trouble.
Here are my questions:
a) Is there a way to ensure that the signal generator is working at 260 kHz, without a frequency counter.
b) If we assume that the signal generator is working properly, I assume that I would adjust trimmer 1 until I hear the generator tone from the speaker. How much adjustment might the trimmers need? I'm not sure if I should be seeing something within a half-turn either direction ... just not sure what to expect. Will the trimmer stop at the end of its travel?
Thanks,
M100C
I am ready to align my Philco 70. I am getting nearby stations pretty good, but I want to properly align the receiver.
I have abbreviated the alignment instructions I got from the Riders manual below:
1) Disconnect the grid clip to the 1st detector. Connect RF signal generator clip to grid of 1st detector and the ground clip to the chassis. Adjust RF signal generator to 260 kc, and dial position on radio to 55. Adjust trimmers 1, 2 and 3, in order, to achieve maximum output signal.
2) Reconnect grid clip on 1st detector. Connect RF signal generator clip to ANT and the ground clip to chassis. Adjust generator to 1400 kc, and dial position to 140. Adjust trimmer 4 to achieve maximum output signal. There are similar instructions for trimmers 5, 6, 7, then 4 again, but that is not the issue right now.
Here's what I've done so far:
- I have an RF signal generator, and I've checked it against a digital receiver (from 530 to 1710 on the AM dial) and I am clearly getting the 400 Hz
internal tone. As I adjust the frequency on the generator, I get the maximum volume from the receiver when pointer is right on the desired frequency (at several points in the AM range), so the generator is working properly and appears to be accurate and graduated correctly.
- To measure output signal, I will hookup my DMM in parallel with the output transformer secondaries and measure VAC. That way, I can hear the speaker and see the voltage.
Here's the problem:
When I do step 1 above, I get nothing from the radio speaker at all (except static). Because the radio works, I am reluctant to give trimmer 1 too many turns ... thus far, I've been careful to keep track of the original settings. Since I cannot tune my digital receiver down to 260 kc, I can only presume that the RF signal generator is working at that frequency; however, it is on a different frequency band. The other frequency bands are working.
When I try step 2 above, I get the generator tone near 140 on the dial ... I should be able to adjust trimmers 4 - 7 without too much trouble.
Here are my questions:
a) Is there a way to ensure that the signal generator is working at 260 kHz, without a frequency counter.
b) If we assume that the signal generator is working properly, I assume that I would adjust trimmer 1 until I hear the generator tone from the speaker. How much adjustment might the trimmers need? I'm not sure if I should be seeing something within a half-turn either direction ... just not sure what to expect. Will the trimmer stop at the end of its travel?
Thanks,
M100C
