[R-390] Z503 Replacement

[Flowertime01 at wmconnect.com]

Don,

Your analysis is text book exact. I accept it as you stated it.
How ever I am not sure I want the AGC response to be as wide as the IF 
response.
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You wrote,

You want the bandwidth of the IF at the AGC detector to be determined 
by the main IF chain, NOT by the AGC IF amplifier, so you want Z503 
to be at least as broadband as the widest IF filter (16 kHz), and 
preferably just a little wider, so that signals at the edge of the IF 
passband are not ignored by the AGC.
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If I am listening with a 16KHZ response it is because I have an AM signal 
that wide. I would like my AGC to follow the fading of that signal. I think 
the AGC should capture the carrier of that signal and provide an audio level 
around that signal. I hate when my AGC goes chasing other signals mixed into 
the band pass and putting more variation on the target signal. Maybe an AGC 
stage filtered narrower than the IF is not a bad thing. A lot of 
assumptions were made to get these receivers into production. Certainly most have 
proven to have been very good over the long haul.

AGC operation has been a topic for a long time. Changing the bandwidth of 
Z503 may not be a wrong idea. It may not cure anything. But some 
experimentation, testing and comparisons could be in order.

I agree that Z503 was made up the way it was is because it was like other 
parts. Same fabrication process, materiel, and test methods. W.W.II 
construction, procurement processes have no relation to the way we manufacture things 
today (Thank God). 

The part needed an isolation cover can. It needed a selected design Q. It 
needed to look like other parts and use as many other similar parts as 
possible. Same bolts same terminals same can cover same core tube blank same wire 
same coil winding machine. 

In early production the hole in the can cover was considered a point for 
contamination to get in. Possible destabilizing factor to tuning. Over time it 
was realized that hole was over kill and left over W.W.II ridged mentality. 
If you have a deck with on hole in the IF cans, you just have early 
production parts. You also likely do not have the trimmer caps under and over the 
mechanical filters.

I am not sure we need to keep Z503 exact as built.

Roger</HTML>