Heathkit SG-8 Signal Generator

[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.

[vortalexfan]

Originally Posted by Notimetolooz

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.

Well the radio only has a ferrite bar antenna and that's it inside it so I was trying to just do a loose coupling by just dangling the test probe next to the ferrite bar antenna to see if I could get a response out of the radio (like I said I I don't have the service manual for this radio because I don't want to pay $25 for it over at Sams and I don't know if they covered it at beitmans or riders because of it being a transistor radio and it was a little after those companies went out of business.)


Also I tried using it to realign my old Philco 116B using the alignment instructions given in Riders and it actually ended up making it worse, and the instructions in the riders called for the IF Alignment to be done by having the positive lead (red lead) of the signal generator hooked up to the grid cap of the 1st detector tube with the grid cap connector out of the circuit (removed from the tube) and then the ground lead connected to the ground connection on the chassis (antenna ground lead).

Which when I did that I was able to peak up the IF really nicely but then when I went to the alignment of the individual tuning bands thats when I had problems on some of the tuning bands I couldn't get the signal to come through, it was completely deaf it wouldn't make any noise but the tuning meter moved though.

The only bands I got response from were the AM Band, the Police Band and the Long Wave Band, the two Shortwave Bands I couldn't get any response from, and once I finished the alignment and I went to test the radio's responsiveness with an antenna, I couldn't get anything in, it was completely deaf.

Is there something I did wrong?

The Philco 116B Manual is posted below.

[Notimetolooz]

Sounds puzzling alright.
What you did with the transistor radio was OK. I don't quite know what to think of the results.

On the Philco, I don't know if the generator they specified has a capacitor isolated output or if it is at DC ground. That would effect the grid bias of the first detector tube, I don't know if that would make a difference to the alignment though. Was the radio working before? The tuning meter moving would mean that something was getting through the IF circuits, it usually works off the AGC generated at the 2nd detector, but maybe this radio is different.
Unless you have that frequency counter or another working radio that can pick up the short wave bands, you really don't know what the SG-8 is putting out.

[vortalexfan]

Originally Posted by Notimetolooz

Sounds puzzling alright.
What you did with the transistor radio was OK. I don't quite know what to think of the results.

On the Philco, I don't know if the generator they specified has a capacitor isolated output or if it is at DC ground. That would effect the grid bias of the first detector tube, I don't know if that would make a difference to the alignment though. Was the radio working before? The tuning meter moving would mean that something was getting through the IF circuits, it usually works off the AGC generated at the 2nd detector, but maybe this radio is different.
Unless you have that frequency counter or another working radio that can pick up the short wave bands, you really don't know what the SG-8 is putting out.

Yes the philco was working before but not very well, it had a lot of issues with not picking up very many stations/not very good sensitivity.

And I could try a capacitor inline with my tester on the philco.
Another thing is that when I had my signal generator hooked up to my philco radio it had a nasty ground loop hum coming through the speaker the entire time.

[Notimetolooz]

Originally Posted by vortalexfan

Another thing is that when I had my signal generator hooked up to my philco radio it had a nasty ground loop hum coming through the speaker the entire time.

If you come across a problem like that hum, you should solve that problem before charging ahead and possibly wasting your time and effort. One thing that you could try to get rid of the hum is reversing the power plug on the radio. Has that radio been recapped? There are caps from the power lines to the chassis in that radio as well as in the SG-8.
When you get a new piece of test equipment the first thing you need to do before using it is to confirm that it is working right.
Do you have a well working AM radio that you can use to see if the generator puts out a signal that you can pick up at the right place on the radio dial? That would test the generator frequency and modulation at least on that one band.
The frequency counter will not be able to test for modulation very well.