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I made several modifications to my SG-8 to see if I could improve the modulation, etc., including adding a tube. I won't go into all I did, it was mostly experimentation and probably not worth it. |
#2
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About that 2420 counter, since it is capable of high accuracy there are a few things you should understand about frequency counters.
The oven crystal oscillator is very stable, however there is an adjustment, a calibration, that is critical so that the display is as accurate as it can be. The oscillator is capable of staying on frequency within better than 1 ppm (one part per million) that is 0.0001 %, much better than any voltage, current or resistance meter measurement. You need that much accuracy if all 8 digits of the display will mean anything. However if the crystal oscillation is only calibrated to an accuracy of, say, 0.1% then the display will be off that much. So the calibration needs to be checked from time to time against a frequency source of even more accuracy. One way is by using super accurate frequency radio broadcasts from stations like WWV and WWVH. More modern methods use GPS managed frequency standards. Last edited by Notimetolooz; 04-23-2020 at 12:06 PM. |
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Last edited by vortalexfan; 04-23-2020 at 04:24 PM. |
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I got the selenium rectifier replaced with a 1N4007 Diode in the Heathkit signal generator.
Picture of the repair is shown below. |
Audiokarma |
#6
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Looks to me like the diode is in backwards....
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You were right it was in wrong, just shortly after I read your comment and I was trying to test it out on an old Zenith Transistor radio I have and I heard a "Pop" noise and I checked it out and sure enough the filter cap that was attached to the diode had vented, thankfully i had a 22 MFD 160 VDC electrolytic in my stash that I was able to replace the vented cap with and now its fine, although I found out that apparently my Zenith radio was way out of adjustment because the 455 kHz IF tone couldn't be heard until around 600 kHz on the radio dial rather than at the end of the dial.
Last edited by vortalexfan; 04-24-2020 at 07:12 PM. |
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The second thing is that the 455KHz from the generator probably is so strong that it will get through the front section of the radio circuit so you should hear it regardless of the dial setting. You should probably not use a direct connection unless the alignment instructions indicate doing it that way. I would use a loop unless the radio isn't working at all. In that case you would be using a type of signal tracing. |
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One way is to tune in WWV at 10MHz using a receiver with an S-meter and zero beating with the crystal oscillator output. Anyway that would be something for another thread. |
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Audiokarma |
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