[captainclock1988]

Hello everyone, the other day I bought on fleabay a Heath-Zenith (Heathkit after Zenith Electronics Corporation of Chicago bought out Heathkit in the early 1980s) Frequency Counter Model SM-2420 that I tried out with my Heathkit signal Generator but it doesn't seem to be working, although I'm not sure if I'm using it right or if I even have the right cables for it. 

I bought from Ace Hardware a 75 0hm rated BNC to BNC cable to go between the signal generator and the frequency counter (the frequency counter has the 2 input jacks listed at 50 Ohms and 1M Ohm (1 Meg Ohm?) and I tried hooking to the 50 Ohm connection and it doesn't read anything on the counter display (well it does but not what the signal is set to), and then I tried the jack marked 1M Ohm and that one doesn't seem to do anything either, so I don't know if its the cable I'm using (wrong resistence of cable) or if this frequency counter is malfunctioning.

One thing is that I finished wiring up the modification that was suggested to me on here by 462ron for my Heathkit SG-8 but I'm not sure if I have it done correctly or not (I posted about it complete with pictures of the completed work in the thread I posted about my Heathkit signal generator), and if it wasn't done rignt maybe that's why my frequency counter isn't responding? 


Also I've never seen a 1 Meg Ohm rated coaxial (BNC) Cable before so how on earth would that work for the input that's marked 1M Ohm?

Also does it matter if I use a 50 Ohm or a 75 Ohm BNC Interconnect cables for going between the Signal Generator and the Frequency Counter?

Any help with this would be appreciated, as this is the first time I've used this kind of equipment.

[W8ZV]

Lets see if I can be of some help here.  Look on the rear of your counter and be sure that it's set for internal on the time-base switch.  If that switch is on the external side, you'll get all zero's

Make sure that your mode switch is on the Freq A position.

Make sure that your trigger control is set to preset.

Those settings should put you in a configuration  that will yield a freq reading when you drive that counter with enough input.

This is a good time to have the discussion of the cable impedance you referred to.  You can use 75 ohm coax with a 50 ohm impedance counter.  What it will cause is an variation in sensitivity of the counter input.  But for what you're trying to do, it should work.  Just for fun though, take your ohm meter and check the continuity of the cable.  Shield to shield and inner conductor to inner conductor.  You want to make sure that the cable is good.  NEVER ASSUME ANYTHING.  Assume makes an A** out of U and ME, to quote my electronics instructor.  If the cables are good, you should be able to get plenty of drive out of your SG-8 (I have one here) to drive the counter.  It will take a lot more drive on the low freq range to get a stable reading. 

Set the output on the generator on the high setting and set the RF output adjustment just above the on position.  Connect the generator and counter together on the 5hz to 50 MHz input and slowly turn up the output adjustment, until you have a reading.  Once you've done that and understand what you have to do to get a reading on the counter with the generator, use a AM broadcast receiver to verify your generator and counter.  Zero beat the generator against a broadcast station whose frequency you know, and then run the generator into the freq counter. 

That will allow you to verify the counter for accuracy with your generator.  Be aware that some generators put out a really ugly sine wave and that will sometimes will cause the counter to read wrong, even though the counter is working correctly.  This Heath counter takes a fairly high level to get a stable output reading.

If you haven't done this yet, you need to get a manual for your counter an read it so you know how it works.

[captainclock1988]

OK, thanks, I do have a manual for it, and according to the manual I have to let it warm up for about 20-30 minutes because of it having a crystal oven inside of the unit, which that was one thing I forgot to do with this thing, also I did check the switch on the back and it was switched to the external time-base rather than the internal time-base so I switched it to the internal time-base settung, and I tried both the "A" input and the "B" input and they both didn't give me any sort of reading (but then again it was probably because I didn't wait 20 minutes for it to warm up).
And its good to know I could use a 75 Ohm BNC cable with this unit because that was cheaper than the 50 Ohm one was.

I did do the modification where I took the AF Input jack and wired it straight to the oscillator so it completely bypasses the Attenuator and has a constant full volume signal.

See the quote below.

[Image: https://philcoradio.com/phorum/attachment.php?aid=22108]    Hi Captain, you can do as you said and just connect the RF OUTPUT to the frequency counter and then adjust the generator to your desired frequency, the disconnect it. My experience with my SG-8 is that it’s not very stable, necessitating constant readjustment. My alteration allows constant monitoring of the generator frequency without constantly connecting and disconnecting the counter to the RF output. Up to you. If you want to do the change, disconnect the AF INPUT jack from everything circled in red, add a .001mfd cap to the jack and the other end to the circuit with the green arrow! Now, no matter what setting you use for the attenuators, the counter always gets full signal level. Using BNC jacks makes it easy to connect a modern lead with BNC ends to the input of a modern frequency counter. This is a fairly quick and inexpensive change to your SG-8!

[captainclock1988]

I got the frequency counter to work, using the tips you suggested, the only problem now is that the signal generator won't output a 400 Hz test tone and signal at the setting that the signal generator is set at, all I get is a buzzing noise out of the radio speaker and that's it.

[W8ZV]

We got you working.  The crystal oven takes 1/2 hour to stabilize.  But you would still be able to use the counter immediately, it just won't be accurate.  As for the 400 hertz tone, you need an unmodulated signal to drive the counter anyway.  You can't read the RF signal with the modulation on.  It will be modulating the RF output and the counter will be reading all over the place.  I haven't tried the mod suggested by the other poster, but if you are running across the generator to use the AF input for an output to drive the counter, you may be introducing noise back into the AF section, unless you used shielded cable to wire that connector.  The best way to get direct drive for the counter is to put an output from the cathode of the RF oscillator.  That way, you get the signal, without affecting the RF output and modulated signal.  It's how HP did it with their older tube based generators.  I don't know what would be required to do that in the Heath SG-8.

[W8ZV]

Update to my last reply:  YUP that mod should work.  It is a cathode follower output coupling already in use.  The output from the cathode circuit suggested will do the job.  Don't have enough coffee yet this AM.  So let's ask this question about the SG-8:  Was the 400 hz tone working before you did this mod?  If it was, then you have created an issue in the AF circuit.  You might have to do some shielding make this work.  Did you replace the filter caps and any other paper caps in the generator?  That can cause issues after using the generator for a while.  They quit working and things get noisy.

[captainclock1988]

Yes its already been recapped, it came to me already recapped and yes the 400 hz tone was working before and even after the modification, but for some reason the tone only worked on bands A, C, D and E but not on B. 

So I'm not sure what's going on.

One thing that I do remember is that I did have thw signal generator hooked up to my radio without a capacitor inline with the test leads because when I was reading through the alignment instructions on the service manual (Beitmans) for the Philco 116B the instructions didn't specify the use of a capacitor inline with the signal generator's test leads, although the instructions specified a specific model of signal generator, a Philco Model 088 Signal Generator which is a Battery Operated version of the Model 077 signal generator that is discussed in another thread in this forum, which if it specifically specified the use of a battery operated signal generator that might be why they didn't specify a capacitor on the antenna lead of the signal generator.
Which if the aforementioned above is the case, I may have inadvertently fried my signal generator by not using a capacitor inline with the antenna lead of my signal generator seeing as it was connected to the grid (top pin) of the 77 (1st detector) tube of my Philco 116B radio which may have sent some DC current into the signal generator resulting in the circuitry being fried.

Also How does the Tuned Harmonics work on a signal generator? I'm asking because both of my signal generators make use of "Tuned Harmonics" to achieve higher frequenices, my Radio City Products unit is rated for AM/FM/SW/LW work and is rated for 100 kHz to 25 Mhz between 6 bands (A-F) and then through the used of "Tuned Harmonics" it can go all the way up to 150 Mhz, and my Heathkit SG-8 unit is rated for 150 kHz to 110 Mhz across 5 bands (A-E) and then through the use of "Tuned Harmonics" it can go all the way up to 220 Mhz, but I'm not sure how that works and I can't seem to find any information on how that works in any of the manuals for these 2 signal generators I have, nor can I find any information on it, by just doing a general google search.

I hope this helps you with helping me figure out what's going on with my signal generator.

[W8ZV]

If you look at the schematic for the SG-8, there is a connection in the tank circuit of the RF OSC that has a common connection with the AF mod output tube, 6C4.  I'd be looking for a cold solder joint at that connection, or an error.

[captainclock1988]

Also I think I may have figured out why my signal generator isn't working, I think my Philco 116B may have become "deaf" so to speak because its not picking up any signals whatsoever on any of its band settings using just a simple wire antenna hooked up to it, which I find very strange, its acting almost like maybe a tube or two in the Radio's Front End may have failed (whether it be the one of the Detector tubes or one of the IF tubes) and unfortunately I don't have any of the tubes that are needed for those positions in this radio, I tried swapping the 1st Detector tube with the 1st Audio tube (both are type 77 tubes) and there wasn't a change in the performance of the set. 
So that only means that either the 2nd Detector tube (37 tube) died or one of the IF tubes (78 tubes) must of failed or something is wrong with the RF stage (78 tube). 

Thankfully I do have several 78 tubes in my stash that I could test to see if the IF Stages may have died or see if the RF Stage died.

[captainclock1988]

If you look at the schematic for the SG-8, there is a connection in the tank circuit of the RF OSC that has a common connection with the AF mod output tube, 6C4.  I'd be looking for a cold solder joint at that connection, or an error.

Hey Kim, I think I found the problem, take a look at the picture below and tell me what you think.

   

[W8ZV]

Very often, you'll find that Heath equipment suffers from poor/missing solder connections.  Sometimes, all I have to do is go back and heat up the connections and add a little solder to cure "problems".  Remember too, that this thing is probably 50 years old or older, and even good solder joints will deteriorate over time due to poor, or substandard, solder.  Use a different radio to determine the generators operation, before you use it to troubleshoot another non working radio.  If you don't do that, your test gear can lead you down a rabbit hole.  You can be trying to "fix" an issue that doesn't exist and creating more issues in the process. 

On your Philco 116, before you condemn tubes, check your voltages in the set.  Have you re-capped the radio COMPLETELY??  Check the resistors values.  It's a pain on a set that large, but you save a lot of time troubleshooting.  If the set was working and suddenly stopped, it's unlikely that it's a tube.  Many times, even when tubes are weak, the set will play, but the performance will suffer.  But it still works.  If you need tubes, I can probably help with that.  I have LOTS of them.  It's far more common for things like the Candohm resistor to open on a section, which takes out the plate or screen voltages, and the set quits.  The Zenith 9S262 I currently have on the bench had four of the five sections in it open.  They are made from Ni-chrome wire, and they open up from over-current (leaking bypass caps) or corrosion.  Even some of the resistors that Philco used in their older radios are not immune to this.  It's also possible that a Candohm will SHORT out to ground.  I've seen that create lots of problems on higher tube count sets.  I make it a practice to NEVER re-use a Candohm resistor.  They get replaced with a new network from individual resistors on terminal strips.  Its also possible that one of the IF transformers has opened up on a winding, or one of the antenna coils has done the same.  Corrosion or a poor solder joint will be the cause.  Your ohmmeter is your friend here.  After 50 years of doing this stuff, I check all the resistors as I recap a radio, AND I check all the transformers for continuity as I go.  Saves time down the road.  The solder back in the '30's wasn't good.  That was 80 years ago.

[462ron]

Hi Captain, your concern whether or not you should have used a cap in series with the RF cable is precisely why I added one inside when I changed over to BNC connectors. That way I don’t need to think about it and it’s less cumbersome than adding the cap to the cable. My SG-8 was my dad’s from the late 50s early 60s and the RF level control was burned out. I figured it must have been exposed to some hv at one time when dad used it, thus the reason I added the cap to the BNC. My conversion that I did works perfectly for me, no noise problems and the 400hz audio is fine, I don’t know what would have happened in your case. Oh, and I should have mentioned too that my frequency counter will go crazy if the internal modulation is turned on, only works properly on an unmodulated RF carrier.
   As for your ‘tuned harmonics’ , if you look at the signal coming from your SG-8 on an oscilloscope, you will see it’s not a pure sine wave at all. It has harmonics of the base frequency in it also. So for example, if you set your generator for 1Mhz, the second harmonic is 2 MHz, the third harmonic 3Mhz. If you have a sw radio tuned to 2 MHz, it will hear your generator that is set to 1 MHz. It is hearing the second harmonic. That is how they extend the range of frequencies on some generators. 

Ron

[captainclock1988]

Hi Captain, your concern whether or not you should have used a cap in series with the RF cable is precisely why I added one inside when I changed over to BNC connectors. That way I don’t need to think about it and it’s less cumbersome than adding the cap to the cable. My SG-8 was my dad’s from the late 50s early 60s and the RF level control was burned out. I figured it must have been exposed to some hv at one time when dad used it, thus the reason I added the cap to the BNC. My conversion that I did works perfectly for me, no noise problems and the 400hz audio is fine, I don’t know what would have happened in your case. Oh, and I should have mentioned too that my frequency counter will go crazy if the internal modulation is turned on, only works properly on an unmodulated RF carrier.
   As for your ‘tuned harmonics’ , if you look at the signal coming from your SG-8 on an oscilloscope, you will see it’s not a pure sine wave at all. It has harmonics of the base frequency in it also. So for example, if you set your generator for 1Mhz, the second harmonic is 2 MHz, the third harmonic 3Mhz. If you have a sw radio tuned to 2 MHz, it will hear your generator that is set to 1 MHz. It is hearing the second harmonic. That is how they extend the range of frequencies on some generators. 

Ron

OK that makes sense, so in the case of the Heathkit, I noticed that when I turned the attenuator knob (RF Output knob) I noticed that when I turned it all the way up to the top of the knob the frequencies being put out by the generator on some bands doubled when being read by the frequency counter, which I take it that the Attenuator Knob (RF Output Knob) is how you use the extended harmonics?

Also as for testing the functionality of the signal generator I have an old Fada model 176 I have torn apart currently that I had recapped completely but was having problems with the tuning pointer binding up when I would try to tune in stations because the plastic dial cover was damaged and the dial pointer was catching on the dial cover so I could test it using that (it needs an alignment anyways) but I also have a couple of old hot chassis radios that need some work that I could test it on, like a 1952 vintage Zenith AM/FM Ciock Radio model J733 but that one requires me to hook directly to the grid of the 12AT7 Converter tube which is under the chassis of the radio which is probably not a good idea with it being a hot chassis set (it does say to use a .05 MFD 400 Volt Blocking capacitor inline with the signal generator, but I'm not going to take any chances and risk shocking myself.)  

So I think I'll use my Fada Radio to confirm the signal Generator's functionality which is not a hot chassis radio and does use alignment instructions similar to the Philco (except that the Fada calls out the use of a Capacitor inline with the Generator unlike the Philco.)

[captainclock1988]

Very often, you'll find that Heath equipment suffers from poor/missing solder connections.  Sometimes, all I have to do is go back and heat up the connections and add a little solder to cure "problems".  Remember too, that this thing is probably 50 years old or older, and even good solder joints will deteriorate over time due to poor, or substandard, solder.  Use a different radio to determine the generators operation, before you use it to troubleshoot another non working radio.  If you don't do that, your test gear can lead you down a rabbit hole.  You can be trying to "fix" an issue that doesn't exist and creating more issues in the process. 

On your Philco 116, before you condemn tubes, check your voltages in the set.  Have you re-capped the radio COMPLETELY??  Check the resistors values.  It's a pain on a set that large, but you save a lot of time troubleshooting.  If the set was working and suddenly stopped, it's unlikely that it's a tube.  Many times, even when tubes are weak, the set will play, but the performance will suffer.  But it still works.  If you need tubes, I can probably help with that.  I have LOTS of them.  It's far more common for things like the Candohm resistor to open on a section, which takes out the plate or screen voltages, and the set quits.  The Zenith 9S262 I currently have on the bench had four of the five sections in it open.  They are made from Ni-chrome wire, and they open up from over-current (leaking bypass caps) or corrosion.  Even some of the resistors that Philco used in their older radios are not immune to this.  It's also possible that a Candohm will SHORT out to ground.  I've seen that create lots of problems on higher tube count sets.  I make it a practice to NEVER re-use a Candohm resistor.  They get replaced with a new network from individual resistors on terminal strips.  Its also possible that one of the IF transformers has opened up on a winding, or one of the antenna coils has done the same.  Corrosion or a poor solder joint will be the cause.  Your ohmmeter is your friend here.  After 50 years of doing this stuff, I check all the resistors as I recap a radio, AND I check all the transformers for continuity as I go.  Saves time down the road.  The solder back in the '30's wasn't good.  That was 80 years ago.

Hi Kim, I looked over the signal generator and that was the only bad solder spot I found as the unit was recapped and all out of tolerance resistors were replaced recently within the past several years.

I don't have very many known good working AC transformer tube sets in my collection right now but I do have one that I recently recapped a 1941 Fada 176 that I recently had to remove from its cabinet again because the dial pointer was hanging up on the old plasic dial cover that was falling apart inside the radio cabinet and it is a known working set (its AM and 2 SW Bands.)

As for the Philco I replaced all of the capacitors except the filter caps as they are still functioning yet (no loud 60 Hz Hum coming out the speaker yet) but I do have the capacitors for that though.
I was able to get the signal generator to work with the Philco 116B a couple of times and I got the 400 Hz tone to work with it and everything the only thing that didn't work on it was when I went to try and align the AM Dial pointer, I couldn't get a 400 hz tone to come out of the speaker when I tried to set it to 1500 kHz to align the 1500 kHz position on the dial or the 600 kHz position on the dial, but it worked fine for the 460 kHz IF Alignment, and the alignment for the 2 SW bands and the LW band and the Old Police Band (now SW 1 band) I just couldn't get it to work in the 510-1610 kHz position on the signal generator, but now I can't get it to do anything on the Philco Radio, but like I said I'll check it out on my Fada radio which is a known good radio.

Thanks.

Levi

[462ron]

It’s strange that the frequency your counter is registering changes with the setting of the RF output level control. If your generator was converted the way we discussed, the output level should have no effect on what the counter sees, hmmm! I know my setup stays the same regardless. If you plan on using it to work on any ‘hot chassis’ set, be sure the set only is plugged into an isolation transformer before connecting any test equipment. If I understand correctly, you aren’t sure if your generator is working in the broadcast band. It should show up on your counter. Or if you have a known working radio, you can put  your output lead from the generator near the radio without even connecting to it and you should be able to pick up and tune in the the signal!

Ron