1. Restoration of a Hallicrafters S-76 communications receiver

  2. General coverage 560 Kc to 32 Mc

  3. AM, CW, and SSB if you carefully tune the BFO

  4. built from 1951-1954

  5. full of wax and paper capacitors

  6. The following additional information is provided:

  7. summary of restoration

  8. service manual

  9. e-mail thread on antique radios.com

  10. Summary of the restoration:

  11. I plugged it in and turned it on.  All panel lights came on except no audio was coming out of the speaker.  After some time the 10 uF wax capacitor C2 started to boil over.  Testing C2 revealed that it was shorted.  I replaced it and was able to get noise out of the speaker but could not tune-in any stations.

  12. I connected an HP606A signal generator dialed in to 10 Mc.  I attempted to tune-in the receiver to this carrier, but no success.  Tracing the signal through the receive chain I discovered that the front-end mixer tube V2 was not producing any IF output.  This prompted me to submit a posting to antiqueradios.com asking about how this type of tube mixer works and what might be the problem.  Here is the conversation thread.

  13. I discovered that the resistors can increase in value as they age.  I found this out by following the suggestions from the replies to my posting.  In the S-76 there are voltage charts that indicate what the DC voltage should be at each pin of each tube.  You must measure these with a proper impedance volt meter, in this case a Simpson 260 with 20k/volt input impedance.  I found that the mixer was not working because the resistors R17 and R18 had increased in value causing V2 into cut-off.  The IF output was strong from V2  once R17 and R18 were replaced.

  14. Tracing the signal throughout the radio I found that R39 and R39 on IF amplifier tube V6 had to be replaced for the same reasons.

  15. After this work a receiver alignment was conducted following the directions in the service manual.

  16. After all of this the S-76 is now working perfectly to its original specifications.  I use it to listen to shortwave and ham band activity.  I thank everyone who helped me on Antiqueradios.com for their support!

Engineering Notes

  1. Service manual

  2. Message thread on antiqueradios.com

  3. Briefings (slide shows)

  4. G. L. Charvat, “Repair and Restoration of Antique Radio Equipment,” MIT Haystack Observatory, October 21, 2009.

  5. The author is not responsible for any injury or death that may occur due to working on antique radio equipment.  Antique radios are dangerous because of the high voltages inside of the radio equipment.  Do not work on antique radios unless you have proper training or experience.  Serious injury or death can occur.  These briefings are for reference only.

  6. Repair and Restoration of Antique Radio Equipment (.pdf)

Restoration of a Hallicrafters S-76 Communications Receiver

Photos of hardware:

April 2009