38-9 Restoration

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The Beginning
Don't Plug it In
10.  2nd Power-On, Success!
The Plan

 1.  Get the Data

 2.  Block Diagram

 3.  Pre-Flight Checks

 4.  What Needs Replacement?

 5.  Ordering Parts

 6.  Install Electrolytics

 7.  First Power-On Checks

 8.  Triage Problems - more trouble!

 9.  Complete Electrical Restoration

10.  2nd Pre-Flight and Power-On, and The Last Problem

Additional Resources

 o  Antenna in the attic

 o  Shortwave Listening Guide

 o  Philco and Radio History

 o  Other Links


100W Bulb Test
Before applying full power, I again inserted the 100W lamp.
To my dismay, it lit!  I yanked the power cord, and pulled out the ohm meter to look for a short.  This was an easy one: the pilot lamp had a frayed wire that was touching the pilot lamp holder.  At this point I rebuilt the pilot lamp holder using the advice from Ron Ramirez's PhilcoRadio website.  Ron has a whole page just for Rewiring Philco Pilot Lamps!

Full Power Test
Now with the 100W bulb out of the circuit, I again applied power and check the chassis voltages.  Much better!  Rather than running low (as before the rebuild), every voltage was at or slightly above the nominal spec.  

The Last Problem
But still this radio was being stubborn.  As before, the Audio noise test was unsuccessful.  I think it was even quieter than before.

At this point I knew I needed expert help.  I still didn't even know if all of the tubes were good. Fortunately, the ladies and gentlemen of the New Jersey Antique Radio Club were holding a repair clinic in Princeton in just a few weeks.  

At the clinic, Aaron was very generous with his time.  First, we checked through all of the vacuum tubes, and they all looked good.  As we looked through the set, Aaron was initially stumped by the lack of hum from the audio section.  He looked more thoroughly than I had at the speaker, and low-and-behold: he spotted the last problem:  The speaker's voice coil wire was broken.  The fact that I had heard something from the speaker mislead me to believe that it was fine.  But I must have heard a ghost effect of the field coil (This is not a modern permanent magnet speaker.  In addition to the voice coil, there is a field coil that is magnetized by a chassis voltage).

Success at last!

After catching a whisker of the remaining speaker wire, the set came on loud and clear!

After celebrating a bit, Steve Goulart (another njarc ace) helped me align the set with his oscillator and scope test gear.  Case Closed!

Listen to a short audio sample from the shortwave band. (mp3)

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Lilian Vernon
Copyright 2004 look4000@verizon.net 
Last modified: November 01, 2008