Several requests have been made to put pictures of the internals of the 20C online - and I've sent the occasional picture or description in email.  Now it's time to actually put pictures of what one looks like on this page.

Keep in mind that this is for the 7570 - and your model may look a bit different.  It is also likely that even for the same model number, slight changes in layout/construction/components were made, so your mileage may vary!
 
 
 

Click on any picture to get a larger version.

The Model 20C, removed from its case. Note the brass tube socket collars typical of the 7570.	A close-up view of the 1st RF stage. The antenna connections are on either side of the tube socket.
The 2nd RF stage (right of center) and the detector (left edge.)  The 250 pf capacitor is under the coil, on the back of the tuning capacitor.	Right-to-left, the detector, 1st and 2nd RF stages.
Underneath the 1st and 2nd RF stages.  Note the 600 ohms wire- wound resistors on the back of the tuning capacitors.	Top view of the AF and detector stages.
Underneath the Detector and AF stages.  The white cylinder on the right edge is the "2-4 Meg" grid-leak resistor.  The 0.002 uf capacitor is to the left of this resistor.	A top view looking down upon the 2nd RF tube socket.  The 0.3uf bypass capacitor is the gray box in front of the socket, between the 2nd and 3rd stage tuning capacitors.
A closeup of the "Antenna Tap" switch.	A view from above the AF/Detector strip showing the audio transformers and the power switch.  The open-frame transformer (which was on the radio when I got it) is a vintage replacement: It's a "DeForest" brand!
Close-up view of the power switch.	Close-up view of the 600ohm resistor on the back of the 2nd tuning capacitor

A few comments:

• The grid-leak resistor is a component that often fails.  If this resistor measures between 1 and 5 megohms, it is probably just fine.  This resistor may take on several forms from a small ceramic tube (like the one shown) to a glass-encapsulated device that looks something like a fuse.  It is also possible for this resistor to have the proper value, but become very noisy.
• On the 7570, it is fairly common to have the 1st AF transformer fail.  On this unit, that apparently happened early on in its life and the "DeForest" transformer was installed as a replacement.  The problem is apparently some sort of galvanic corrosion where the transformer windings were connected to the external leads.
• It is common for the coil windings to break loose.  For the internal windings, a drop or two of plain white glue will work (don't go overboard.)  For the exterior windings, a drop of shellac or diluted white glue may be used.

Click here for a redrawn schematic of this radio.
 

An AC-Operated power supply for the Atwater Kent Model 20 Compact Receiver.

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Any comments or questions?  Send an email!