38-9 Restoration

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The Beginning
Don't Plug it In
2.  Understand the Block Diagram
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


Basic Block Diagram

There are far more detailed tutorials available elsewhere (see references), but understanding this simple block diagram is helpful in determining where problems lie.  I'll refer to this block diagram in the following sections as well.

So here's my attempt at a 30 second tutorial on how a radio operates:

  1. The power supply converts input power to usable voltages.  Input power is typically AC wall power (though battery operated (DC) and combination AC/DC sets are common as well).

    The power supply contains a rectifier tube that converts AC to DC, and electrolytic capacitors that smooth the resulting voltage.  These are the caps that are always trouble with age.

    DC power is supplied to the Receiver and Audio Amplifier sections.

  2. The receiver pulls in radio signals from the antenna and converts them to audio signals, albeit at very low strength.  The IF oscillator, Detector, and IF Amplifier are within this stage.

  3. The Audio Amplifier takes the very weak audio signal from the Receiver, and amplifies it, driving the speaker.  Volume and tone controls are also within this stage.


If you can identify these three main areas of your schematic, then you'll be in great shape to isolate issues and determine the health of each stage.

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