Heathkit SG-8 Signal Generator

[Notimetolooz]

Originally Posted by vortalexfan

What size of resistor should I use if I were to replace the old selenium with a 1n4007 diode?

Since there is a 3.3K resistor in the filter circuit, which suggests there isn't much current draw, I ended up not adding a resistor.
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.

[vortalexfan]

Originally Posted by Notimetolooz

Since there is a 3.3K resistor in the filter circuit, which suggests there isn't much current draw, I ended up not adding a resistor.
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.

OK, so then I can just take out that Rectifier and just replace it with a 1N4007 and be done with it.

[Notimetolooz]

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.

[vortalexfan]

Originally Posted by Notimetolooz

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.

So basically the atomic clock stations in Fort Collins, Colorado and Kekaha, Kauai, Hawaii?

[vortalexfan]

I got the selenium rectifier replaced with a 1N4007 Diode in the Heathkit signal generator.

Picture of the repair is shown below.

[N2IXK]

Originally Posted by vortalexfan

I got the selenium rectifier replaced with a 1N4007 Diode in the Heathkit signal generator.

Picture of the repair is shown below.

Looks to me like the diode is in backwards....

[vortalexfan]

Originally Posted by N2IXK

Looks to me like the diode is in backwards....

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.

[Notimetolooz]

Originally Posted by vortalexfan

, 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.

There is something else wrong. First of all 455KHz is out of range of the AM radio dial, it usually doesn't go below 540KHz.
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.

[Notimetolooz]

Originally Posted by vortalexfan

So basically the atomic clock stations in Fort Collins, Colorado and Kekaha, Kauai, Hawaii?

Right. Probably more than you really need. Just wanted to let you know how involved things get when you deal with things at high accuracy levels.
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.

[vortalexfan]

Originally Posted by Notimetolooz

Right. Probably more than you really need. Just wanted to let you know how involved things get when you deal with things at high accuracy levels.
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.

Couldn't I just tune it in on one of my old shortwave radios? Also what's an S-meter and wh as t do you mean by zero beating with the crystal oscillator output?