[R-390] RE: Antenna Trimmer

[Roy Morgan]

At 07:28 AM 7/15/2004 -0500, Laird Tom N wrote:
 >... the insulating bushing and thrust washer for the shaft

Are there to insulate the rotor of the capacitor from ground.  The antenna 
trim cap is connected across whichever RF input transformer is selected by 
the band switch.  The RF Transformer secondary winding carries the AGC 
voltage to the grid of the first RF Amplifier tube.

Note:
That shaft is then a convenient place to test the AGC voltage that is 
getting to the 1st RF stage in trouble-shooting the AGC system. Use a VTVM 
of the old style with a 1-meg-ohm resistor in the probe to avoid detuning 
the stage.  The 11 or so megohms of most DMM's or VTVM's may not affect the 
DC values much, but be alert for that happening to some degree.  Test point 
E-208 is tied to the first RF Grid through a 470K resistor and is meant for 
just this purpose.  It would help you confirm an open RF Transformer, or 
bad contacts on the transformer plug pins or the band switch.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
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