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 Post subject: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 4:19 am 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Hello all
Does anybody know of a newer schematic for this heathkit IG-102. This one has definitely been modified in the past. Looks nothing like the original sch.
Mine doesn't have any attenuation at all.. The pot and switch for high and low do nothing. I was looking to try and fix it but it's nothing like the schematic.

Would the best thin be to tear it apart and start over or see if there is a modification schematic somewhere? Thanks for any ideas

Dick


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 5:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18307
Location: Albuquerque, NM 87123
The output circuit of the IG-102 is really basic; just a control and a three position switch with a few resistors and a capacitor. The resistor network approximates 50 ohms impedance.

Is the three position switch still there or missing? That part would be the hardest to find.


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 6:02 am 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
The switch is there but according to the schematic it should have 2 680 ohm resistors and 2 47ohm resistors on it. Mine has 6 resistors on it, 3- 47ohm---2- 88 ohm and 1-380 ohm. And they are not at all attached like the schematic. Plus it has a shielded wire running from the on off switch to a terminal board by the V2 tube .

The switch and pot for fine attenuation is there but they don't function at all.
I see your attachments now. Yea that's exactly the way the schematic and assembly manual show the switch. I'll get a pic of mine in a few minutes.
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Attachment:
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IMG_20190211_001412131.jpg [ 57.4 KiB | Viewed 287 times ]

Thanks

Dick


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 12:21 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 3461
Location: Sunbury, Ohio 43074
It looks like perhaps someone did a home brew mod to .... ???? maybe change the output impedance, or output ranges, to match what they wanted to use the generator for? Perhaps if you can sketch out what was actually done, and is in your generator now, we can figure out what the intent was. If the output attenuator does not do anything, that might indicate that the modification was not done properly in the first place.

It looks like it would be simple enough to restore it to the original wiring, assuming that the ceramic switch has the same contact and wiper arrangement as the original Heathkit switch. You can check that by drawing it out as well, and comparing it to the Heath schematic.

I suppose it is also possible that Heath did change their production line at one point. But if so, it should at least function.

When you are measuring the output and exercising the attenuator, do you have a load hooked up at the same time? If not, try one. A resistor will do.

And lastly, or perhaps firstly, when you note that the attenuator "does not function at all" ... I assume that there IS signal out and you just cannot vary it??? Or is there no signal. If the latter, the generator may be not generating.

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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 2:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18307
Location: Albuquerque, NM 87123
That control and switch are not Heath. Those resistors look like 510 ohm and 56 ohm; is the switch 4 position? Is there any RF coming out at all? The original RF control was 3K; not a common value so they used 2500.

If you have a scope I would check for RF at the control. Also, there is some type of diode or transistor at a terminal near the 6AN8; this is not original. May be other things different also.


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 7:17 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
Looks like it may have been changed from a three position to a four position attenuator.

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 8:38 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
You guys are right --- it is a 4position attenuator and yes I get an RF tone but there is no adjustment. It is ear splitting when trying to align a radio and the volume has to be full. If I can keep the volume down on the radio it's alright and I can locate some problems with it but I would like to have the needed adjustment.

I think I'm just going to take all the mods out and restore it to the original schematic. Sound like a good plan?


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 8:53 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 3461
Location: Sunbury, Ohio 43074
restoring it to original should work, but also if you draw out what is there and post it here we can probably tell if it shoujld work the way it is.

I'm not sure what you mean by "RF TONE" .... RF is out of the range of hearing. I assume you are injecting an RF signal somewhere into the radio and that is making it scream?

You may be doing it wrong. Describe exactly what you're doing, at what point you are injecting the RF into the radio, and I'm sure one of the radio guru's here can steer you from there.

Do you have an oscilloscope? If so, put it across the generator output while it's hooked up to the radio, and see if the attenuator varies the level any.

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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 9:19 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
I'm sorry I misspoke. I put a modulated signal into different parts of the radio to make sure everything was working. I'm fine with that because I can regulate the volume on the radio. But when trying to align with this sig gen I have no attenuation so I can't adjust to the quietest signal.

I don't have a oscilloscope and wouldn't know how to use it if I did. I'm one of these semi-noobies that is still wallowing around in the mud.
I'll see if I can find a schematic to post and post the changes that are on this gen.
file:///C:/Users/Admin/AppData/Local/Packages/Microsoft.MicrosoftEdge_8wekyb3d8bbwe/TempState/Downloads/heathkit_ig-102_rf_signal_generator%20(1).pdf
Thanks for everything I hope that works

Dick


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 10:45 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18307
Location: Albuquerque, NM 87123
The IG-102 has fixed audio modulation (around 30%). On some RF generators you can adjust modulation level but not on this one.
With that control and attenuation switch you should be able to adjust RF output level; you would only be able to see it change with a scope. On a radio, especially one with AVC, you would not hear a difference until the RF level dropped below a usable amplitude. Note: when doing alignments it is usually best to have the generator at the lowest signal that gives a clearly readable level.

The IG-102 manual has instruction on use.

The audio in your generator may have been modified.


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Mon 11, 2019 10:53 pm 
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Joined: May Wed 18, 2011 2:40 am
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Location: Littleton, MA
The modifications look to be quite well done. The extra shielding is a nice touch, as is the ceramic rotary switch. I wouldn't undo them without digging deeper into why the attenuator isn't working. Have you measured the resistors in the attenuator? Do the values match the color codes?

Did the previous owner add a high-level output for a frequency counter?

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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Tue 12, 2019 4:54 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 1376
Location: Dallas, TX
Yes, I would suggest you evaluate how you are using the generator before you change the generator.
Most RF generators put out far more signal than what would be required at the antenna input. Microvolts
of signal is all that is needed there. How are you coupling the generator to the radio? You can just use a coil
of a couple of turns of wire connected to the generator output. If you use something more direct you could be
maxing out the input at the smallest generator output and the higher output can't make the sound any louder.
Unless something is shorting an attenuator circuit should be changing the output. If you had an RF meter or o'scope that worked at the RF frequency you should see a difference in output.

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Tue 12, 2019 8:48 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18307
Location: Albuquerque, NM 87123
This is the schematic for your new attenuator circuit; it should work. It is shown in High position, where your switch is shown in the picture. C28 looks like it got twisted around a bit--it may be bad. That is the .01uf disc cap that connects to the output connector.


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 Post subject: Re: Heathkit IG-102 mods
PostPosted: Feb Tue 12, 2019 6:59 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Thanks Tim I think I figured out something. Yesterday I sprayed contact cleaner in the Fine Atten. pot and cleaned the switch even though they looked clean. I just hooked it up to this American Bosch 515 and on the RFout jack hooked up to 1st IF tube 6D6 I can now adjust the tone with the Fine Atten knob and the coarse knob. The Fine pot is still scratchy so I'm going to do some more cleaning. Thank You for your considerate help.

Also Johnny Thanks for the schematic. I'm going to check that cap after cleaning the Fine pot again.

Thanks to you both


Dick


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