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<DIV>Hi</DIV>
<DIV> </DIV>
<DIV></DIV>
<DIV>You need to do some measurements around the AGC and IF amplifiers to see
what is happening at various signal levels. The AGC line should measure as
a high resistance with the AGC switched on, the SB300 switched off and cold.
Then switch on, connect an aerial and start with the AGC detector
output at the anode of CR1.</DIV>
<DIV> </DIV>
<DIV>The AGC line should go more negative with increasing signal strength which
will cause the controlled IF stages to reduce their anode current and the
voltage drop across the cathode resistors to reduce. The change in cathode
current in valve V7 is used to drive the S meter.</DIV>
<DIV> </DIV>
<DIV>It has been noted on the Heathkit forums that there have been some leaky
6AU6 valves which cause the AGC line to become positive and therefore not work
correctly.</DIV></DIV>
<DIV> </DIV>
<DIV><FONT lang=0 size=2 face=Arial FAMILY="SANSSERIF"
PTSIZE="10">73<BR></FONT><FONT lang=0 color=#0000ff size=4 face=Arial
FAMILY="SANSSERIF" PTSIZE="14"><I><BR>Bob</FONT><FONT lang=0 color=#000000
size=2 face=Arial FAMILY="SANSSERIF" PTSIZE="10"></I><BR>Bob F Burns G3OOU<BR>C
Eng, FIET, MSE<BR>G-QRP 6907<BR>Secretary of Crystal Palace Radio &
Electronics Club: www.g3oou.co.uk<BR>Technical web site:
www.qsl.net/g3oou<BR>@BobFBurns on Twitter:
http://twitter.com/BobFBurns</FONT></DIV></FONT></BODY></HTML>