Heathkit SG-8 Signal Generator

[Electronic M]

It's not a bad idea to replace the original selenium rectifier in it with a modern 1N4007 or similar as preventive maintenance or you can be a Daredevil and run it with the original till it smokes.... I've taken both approaches.

[vortalexfan]

Originally Posted by Electronic M

It's not a bad idea to replace the original selenium rectifier in it with a modern 1N4007 or similar as preventive maintenance or you can be a Daredevil and run it with the original till it smokes.... I've taken both approaches.

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

[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....

[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?