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Heathkit IG-42 Laboratory Generator – Initial Checkout


Heathkit IG-42 Laboratory Generator – Initial Checkout

I hooked up the Heathkit IG-42 Signal Generator to the variac on the bench and brought the voltage up slowly, watching for signs of overheating or failed components.  There was a slight hum coming from the unit for the first couple of minutes, then it got better.  I suspect that the electrolytic capacitors were recovering after having not been in use for some time.

The IG-42 is rated for 100,000 uv output, with a 50 ohm output impedance.  To check this against a known good source, I set up my HP 8640B signal generator for 0.1 volt output into the 50 ohm terminated input of my scope.  0.1 volt = 100,000 uv.

8640B Check Scope Calibration

As the photo shows, I have about 0.28 vpp showing on the scope.  To get the rms value from the vpp value, you first divide by 2, then multiply by 0.707

0.28 / 2 = 0.14
0.14 x 0.707 = 0.09898  or approximately 0.1 vrms

8640B Output at 100,000 uv RMS

So, I know that if I can get a similar 0.28vpp waveform from the Heathkit, it is meeting the output level specifications.

I set the IG-42 frequency to near mid scale (about 1.6 Mhz, in this case), and set the Microvolts control to x10K.  So when the meter is at 10, then the output should be close to 100,000 uv, or 0.1 volt rms into the 50 ohm load.

IG-42 at 100,000 uv output on meter

When I looked on the scope, there was no output shown…

IG-42 No Output

After tapping on various parts of the case, and wriggling the output cable, I found that if I held the output cable up at an angle, I could get an output.  So it appears that the first issue is a poor connection on the connector that plugs into the IG-42.  The waveform is not a great sine wave, but is typical of what I have seen from other Heathkit signal generators of this vintage.

IG-42 at 100,000 uv

On each of the 5 bands, I was able to obtain 100,000 uv output with the meter approximately at the full scale “10” value.

Band A – 100 Kc – 290 Kc

Band Selector

167 Khz Output

Band B – 280 Kc – 1000 Kc

488 Khz Output

Band C – 0.95 Mc – 3.1 Mc

1.6 Mhz Output

Band D – 2.9 Mc – 9.5 Mc

5 Mhz Output

Band E – 9.0 Mc – 31 Mc

15 Mhz Output

So, what next?
I think I will begin replacement of all of the paper capacitors, along with the electrolytics.  I will replace the two caps across the line input with X1Y2 rated safety capacitors.  I still need to decide on whether to replace the power cord or not.  Since it is across the transformer primary, and isolated from ground, it really doesn’t matter which line is on hot or neutral. Particularly with the swap to the safety caps across the line, from the original disc ceramic non-safety rated caps.  But I might still convince myself to do it.

The RG-58 cable that connects to the output will need to be repaired or replaced.

Finally, a cleanup of the cabinet and maybe knocking the dent out might be in order.

Stay tuned for updates…



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