Heathkit SG-8 Signal Generator

[Notimetolooz]

Originally Posted by vortalexfan

I'm assuming with a transistor radio you don't need a capacitor inline with the test leads like you do an AC powered set.

Also I got tons of line interference through the signal generator similar to the line interference I said I had been getting on my radios.

Do you have a copy of the manual?
http://pdf.textfiles.com/manuals/SCA...thkit-SG-8.pdf
You should have a manual for all your equipment.

If you look at the schematic you will see that the RF output does not have any DC blocking capacitor, therefore if you connect it directly to the a point in the radio that has any DC voltage on it that point will be connected to ground through the resistors in the generator output circuit. When in doubt use a external capacitor.
Also the two capacitors in the generator that are connected to the power cord and ground can put a 60 Hz signal on the case. With a battery powered radio the ground connector of the RF cable needs to connected to the radio. A small capacitor in the signal line to the radio will block the 60 Hz but pass the RF. If you use a coupling loop on the generator output you don't need the capacitor.
Another thing, I added a 0.01 uf capacitor in the generator between the wiper of the output pot and the output switch pin 7. There is a DC current running through the output pot from pin 3 (cathode) of the 12AU7. This can cause a DC voltage on the output.

[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.

[vortalexfan]

Originally Posted by Notimetolooz

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.

Well the problem is, the hum went away as soon as I disconnected the signal generator and reattached the 1st Detector Tube's Grid Cap and ran the radio like normal.

Also I figured out why the Philco Signal Generator Specified in the service manual to align my Philco 116B radio doesn't need a capacitor inline with the positive lead of the signal generator, its because its a battery operated unit so it doen't have to worry about DC current on its parts like an AC powered unit would, so DC Current leakage from an AC powered Radio isn't going to affect its circuitry since its a purely DC Circuit design to begin with.

Hope that helps.

[dieseljeep]

Originally Posted by vortalexfan

That's what I thought. The guy on the Philco Phorum basically said the same thing. But the thing is, I'm just repairing old tube radios and stereo receivers so lab quality gear like the Hewlett-Packard units are not what I need.

I just need something to get me close enough to make the radios work again as intended, it's not like I'm designing new radio circuits where you would need something like a lab grade unit for.

Most of the units I'm repairing are units that are already working circuits but just need to be touched up, so a regular bench grade unit is more than enough for the work I'm doing.

When I was acquiring test equipment in the early 60's, I bought Allied Knight Kit equipment because they had a store in Milwaukee and I didn't have wait for mail order. Most of my test equipment was kit form. I was in my early teens at the time. It was good enough for simple alignment procedures.
Later on, I was able source a GI unit that was more impressive and stable.
I am really amazed at some of the test equipment that is available today.

[vortalexfan]

Originally Posted by dieseljeep

When I was acquiring test equipment in the early 60's, I bought Allied Knight Kit equipment because they had a store in Milwaukee and I didn't have wait for mail order. Most of my test equipment was kit form. I was in my early teens at the time. It was good enough for simple alignment procedures.
Later on, I was able source a GI unit that was more impressive and stable.
I am really amazed at some of the test equipment that is available today.

I had a friend I went to church with who built an old Allied Knight Kit Stereo System that he built a solid walnut Console Cabinet for when he was in High School back in the 1960s (he's probably about the same age as you are), and it had a push-pull 6BQ5 Amplifier, a Stereophonic AM/FM Tuner with a Magic Tuning Eye Tube for the tuning meter, and a Warwick Built/Sourced 4 Speed Record Changer, and a set of Knight 3 way Coaxial Speakers all built into the solid walnut console cabinet that he had built for it in shop class when he was in High School.

Unfortunately by the time he gave me the unit the amplifier's power transformer was blown, so I salvaged the tubes out of the unit and installed an old Kenwood amplifier into the cabinet to continue using the tuner and turntable and speakers but then the tuner died as well and so I ended up saving the tubes out of the tuner and scrapped the rest of the unit out and sold the Kenwood amplifier and just used the cabinet for my LCD Projector Video system since.

[Notimetolooz]

Besides a loop of wire mounted on a little stand I also have a couple of capacitors, 0.01 uf and 0.1uf, each one with a small alligator clip on one lead, to use with my generator.
The voltage rating can be fairly low, NEVER connect to generator to the plate side of a tube. If the instructions call for a cap, or I think I need one, I clip the hot lead from the generator to one cap lead and use the clip on the cap other lead to connect to the radio.
Here is a link to the Antique Radio Forums Archives. They scanned in a book from 1947, "Elements of Radio Servicing". Of course equipment like frequency counters, dual channel oscilloscopes, etc. were uncommon or non-existent in 1947.
https://antiqueradios.com/archive.shtml
No clubs are meeting now because of the virus, but generally they are a good resource. There is a fellow in the club I'm in who presents quite a few technical talks. Sometimes the text is kept online. I don't know if he was a teacher or something. Here is one by Mike McCarty about aligning radios.
http://vrps.org/documents/Alignment.html

[vortalexfan]

Originally Posted by Notimetolooz

Besides a loop of wire mounted on a little stand I also have a couple of capacitors, 0.01 uf and 0.1uf, each one with a small alligator clip on one lead, to use with my generator.
The voltage rating can be fairly low, NEVER connect to generator to the plate side of a tube. If the instructions call for a cap, or I think I need one, I clip the hot lead from the generator to one cap lead and use the clip on the cap other lead to connect to the radio.
Here is a link to the Antique Radio Forums Archives. They scanned in a book from 1947, "Elements of Radio Servicing". Of course equipment like frequency counters, dual channel oscilloscopes, etc. were uncommon or non-existent in 1947.
https://antiqueradios.com/archive.shtml
No clubs are meeting now because of the virus, but generally they are a good resource. There is a fellow in the club I'm in who presents quite a few technical talks. Sometimes the text is kept online. I don't know if he was a teacher or something. Here is one by Mike McCarty about aligning radios.
http://vrps.org/documents/Alignment.html

Ok, thanks, I'll keep that in mind. I do have a .1 MFD and a .01 MFD capacitor in my stash I think so I'll just rig them up to alligator clips.

[vortalexfan]

...

[vortalexfan]

OK, I have a question about my Heathkit Signal Generator,
Band 1 works fine and produces a the 400 Hz test tone for the IF Alignment like I need it to, but when I go to use Band 2 which is the 550-1600 kHz band used for aligning the AM tuning band on the radio dial it doesn't produce any sound, but it does on Bands C-F which are for SW and Long Wave and FM Alignment work.

Is it possible that there's something wrong with the circuitry inside the signal Generator that's causing it not to produce the 400 Hz test tone on Band 2 of the signal generator, like a bad tube or a bad coil?

Any help with this issue would be great.

By the way I am using a blocking capacitor inline with the test leads on this signal generator.

Also I just got my new (to me anyways) Frequency counter and I need to get a Male BNC to Male BNC cable so I can hook my signal generator to my Frequency Counter, and I see a 50 Ohm version and a 75 Ohm version, does it matter which verion I use or do I need to use the 50 Ohm version for proper function of the frequency counter?

Thanks for your input on this matter.

[vortalexfan]

OK So a little update on this Signal Generator:

My SG-8 is having some problems that may or may not be related to a modification I did to it to it so that I could have continuous Monitoring of the signal generator with a frequency counter, apparently the first 2 bands on the signal generator (Bands A and B) put out a 400 Hz test signal but its not very loud, and then Bands C-E don't put out any 400 Hz test signal at all just a loud humming noise that is somewhat affected by the RF Output Knob.

Any Ideas as to what could be causing this issue?

What say you Notimetolooz?

[Notimetolooz]

The standard output impedance for a RF generator would be 50 ohms, so that would be the best coax type. However low cost generators like the SG-8 don't bother with exact impedance. An attenuator that is marked in db will not be correct if the connecting impedance is wrong, but otherwise it doesn't matter unless the coax is very long. 75 ohms is used for a few things like TV RF and video signals.

The same modulation is used on all bands in the SG-8. The modulation puts a audio sinewave on the output tube grid along with the RF. This is not the best way to modulate the RF, but it works OK. It is possible that the audio is changing the tube bias somehow and effecting the operation.
The frequency counter will only function correctly without modulation. You need to use a working radio or an oscilloscope to check fo modulation.
I don't know exactly what you did and I don't know how you did it, so I can't know what the problem might be.