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Heathkit IG-42 Signal Generator Restoration – Part 1

 

Heathkit IG-42 Signal Generator Restoration – Part 1

Filed in Heathkit IG-42 on Apr.02, 2018

The first fix applied to the IG-42 Signal Generator was the replacement of the 0B2 regulator tube. With the new old stock replacement, the B+ voltage dropped from 131 vdc to about 107vdc. The 0B2 is a 108 volt regulator, so that should be about right.

The new tube voltage chart is displayed below. I have not replaced any resistors or capacitors at this stage, so these readings may change again in the future, but they are much closer to specifications, now.

TUBE Pin1 Spec Pin1 Actual Pin2 Spec Pin2 Actual Pin3 Spec Pin3 Actual Pin4 Spec Pin4 Actual Pin5 Spec Pin5 Actual
6AF4 65 71.9 10 - 30 Neg. -11 0 0 5 - 7 AC 5.9 0 0
6AV5 0 0 5 - 7 AC 5.9 12 12 0 0 100 112
12AU7 60 70.2 1.0 Neg. -1.2 2 1.86 5 - 7 AC 5.9 5 - 7 AC 5.9
OB2 100 106.8 0 0 0 0 0 0 100 106.8
                     
TUBE Pin6 Spec Pin6 Actual Pin7 Spec Pin7 Actual Pin8 Spec Pin8 Actual Pin9 Spec Pin9 Actual    
6AF4 10 - 30 Neg. -11 65 71.6            
6AV5 0 0 0 0 100 106.7        
12AU7 100 112.3 30 34 33 35.7 0 0    
OB2 0 0 0 0    
 
   

After replacement of the OB2 regulator tube, I continued the work of replacing all of the old paper capacitors.  Here is a photo of the modulator/power supply chassis prior to their replacement.

 
Audio and Regulator Tube compartment

And here is a photo after replacement of the caps in that section.

 
Paper Capacitors replaced in the modulator/power supply section.

The red capacitors in the photo above are all 0.05 uf polypropylene caps. The yellow ones are metalized polyester film caps.

I also replaced the 68K resistor that was on pin 2 of the 12AU7 tube with a 47K resistor, as specified in the manual.

Next we will pull the metal cap tri-section capacitor and attempt to re-stuff it with modern electrolytic capacitors. Check out my next post for details…

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