Heathkit SG-8 Signal Generator
 

Hello everone I just bought on fleabay a Heathkit SG-8 Signal Generator that I intend to use to help me realign the radio that I restore, the unit itseld is in near mint condition, but the unit doesn't have its original probes with it anymore and it doesn't have its manuals anymore either.

I was wondering how hard it would be to source some probes for this unit or to make some, and if I could get a manual for this thing online somewhere?
Would also like to know how to use one of these with radio alignment.

Any help would be appreciated.

There is a little thing called "Google". You ought to try it sometime.
http://pdf.textfiles.com/manuals/SCA...thkit-SG-8.pdf

The connector used on that unit are what was known as microphone connectors. The end that goes onto the cable end can be found but a better solution is to replace the connectors on the generator with BNC jacks. There are even pre-made cables with BNC plugs made. I believe that the stock cables were coax with alligator clips on the other end.
There are a number of sources for general instructions on AM radio alignment. Usually the service data for each radio gives further details.
Most of the time you can connect the generator cable clips to a small coil of wire (4-6 inch diameter) with something like 8-10 turns. This coil sends a signal to the radios antenna loop. Some radios don't have antenna loops and the coupling is done another way. Sometimes the signal is injected into the radios IF circuits various ways.
I recommend a book like this one.
https://www.amazon.com/Old-Time-Radi...s=books&sr=1-1

This is the type of BNC jack you could replace the microphone connectors with.
https://www.mouser.com/ProductDetail...zdb4bk0FGlA%3D

Yeah, I ended up finding the manual after someone on the Philco Phorum told me about it, (I wrote this thread before I saw the reply on the Philco Phorum).

Anyways I also bought a Radio City Products Model 705A Signal Generator that also needs test leads and a manual.

Although I'm kind of regretting asking about those signal generators on the Philco Phorum because the person who replied to my thread on there is trying to make me feel bad about my purchases by telling me that they are going to be crappy and telling me that I should of instead bought a Hewlett-Packard one instead (even though I could never afford to buy one).

Well the Heathkit doesn't have a very nice sine wave output but it usually does not matter. The SG-8 like many generators used for radio-tv repair are what is known as "service grade" as opposed to "lab grade". A sinewave that doesn't have the right shape has harmonic distortion. That means that a 1Mhz output also could contain 2MHz, 3MHz, 4MHz, 5MHz, etc. Many times just the odd harmonics. However the tuned circuits in a radio-tv reject the harmonics for the most part, so they don't really matter in practice.
Also the service grade generators do not keep the signal amplitude the same as you change the frequency. However you can monitor the amplitude if you need to and adjust the amplitude as you change frequency. Maybe not as convenient, but you can make it work. Most of the time you don't change the frequency that much anyway.
The frequency dials on service grade generators are not as accurate so if you must have the frequency exact a frequency counter is a good addition to the set-up.

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.

I've gotten working 70s HP gear for under $10 before. It is all a matter of being in the right place at the right time.

Some many service generators are inaccurate enough on frequency that if you don't have a frequency counter to check them they can sometimes mess up alignment. Some frequency counters will get confused if the carrier is not sinusoidal enough. My old lab grade generators lack modulation capability (which is important for some alignment work) so I calibrate my service grade generator by dialing the lab gen to the right frequency on the counter, connecting the lab gen to my scope, counting the time divisions with 1-3 cycles on screen, then connecting the service gen and dialing it for the same number of time divisions.
If you haunt enough big ham radio swapmeets you'll eventually have enough decent budget equipment.

Well the problem is, there are no swap meets near me, and trust me, I've already checked, the closest ones to me are in Indianapolis, and Chicago, and I don't want to drive to those areas because they are horrible to drive around.

The cheapest Hewlett-Packard signal generators on eBay are $150 and $50 shipping, there's no way I can afford that on my meager budget.

Fort Wayne?

http://fortwaynehamfest.com

jr

That's another city I'd rather not drive around in because traffic is terrible there and my mom doesn't want me to drive around there unless someone is with me for the reasons I mentioned.

Plus activities like that are canceled until further notice because of the corona virus.

It is great that HP equipment is more affordable now. I have some myself and I don't usually spend a whole lot on things. That being said, you have to keep in mind that a piece of HP test equipment built in the 1950's will require re-capping just as a radio or TV from that era. HP used very high quality parts so they hold up better than others, but there are limits on how well anything lasts. Solid state test equipment made more recently are less likely to need restoration before they can be used. Repair shops in the 40's through the 70's seldom had HP equipment.
There are brands that fall between HP and say Heathkit in precision. Heathkit items are very easy to work on since they were intended for assembly from scratch. There are service grade brands with better performance that are factory built but are simpler than HP. B&K, RCA, EICO, Sencor, Leader and Tektronix, etc.
Here is my modified SG-8. My B&K 2005A RF generator and HP 5382A frequency counter. Also my Leader LAG-27 audio generator, a home-built 455KHz generator and my RF coupling loop. I think I found the SG-8 locally on Craig's list. The others were very carefully selected form ebay. The B&K RF generator had some broken front panel pieces (poor packing) that I was able to glue back together. Except for the SG-8 the equipment shown is solid state, but I think I replaced the electrolytics in all of them.

OK, thanks for the info.
I'm just curious, how do you hook up a frequency counter to a signal generator if I got one?

Good question. That points out a bit of a problem normally. The output of a typical RF generator is very small. It only takes something like 10 uV ( 10 one millionth of a volt) of signal at the radio antenna for the radio to receive it. The problem is many frequency counters need something like at least 100 mV for them to work. One thing to do is turn the generator output up to max to read the frequency and then turn the output down before connecting to the radio. Another thing that sometimes works is to modify the generator and bring out the signal before it goes into the output attenuator to a separate connector. The B&K 2005A has this already done. It has the normal output connector that the amplitude can be varied and a frequency monitoring output connector. Some people have bought small frequency counter modules and install them in the generator if there is room. I don't think the modules have a very precise timebase oscillator in them however.

It the counter is microcontroller based and has a crystal osc it can be very precise.

Depends on how good the crystal oscillator is more than anything. You get what you pay for.