[R-390] A bit more on my IF deck

[JMILLER1706 at cfl.rr.com]

Let's see.... from pin 2 of V-506 it looks like paths to ground are:
R547 (220K) + R544 (2.7M) to ground thru whatever resistance to ground 
is in the B+ line in the power supply.
In parallel with:
R234 1.5M which is on the AGC line in the RF chassis.
What's the math for those parallel resistors?  I get about 1M, which 
doesn't agree with the 500K you're reading...is there another 
resistance to ground I am missing?  Look all along the AGC line to see 
if there are others in the RF deck...I can't find any others.
Or am I reading this all wrong?


----- Original Message -----
From: "n4buq at knology.net" <n4buq at knology.net>
Date: Tuesday, March 7, 2006 11:46 am
Subject: Re: [R-390] A bit more on my IF deck
To: JMILLER1706 at cfl.rr.com, R-390 at mailman.qth.net

> Oops!!!  In my post below, I wrote Pin 6 of V506.  I meant Pin 2 
> of V506A 
> (the grid of the AGC Time Constant Tube).  Sorry.
> 
> Barry - N4BUQ
> 
> > Isn't V-506B the AM detector?  If I am reading the schematic 
> right, V-
> > 506B doesn't connect to the RF deck,... I htink it connects to 
> the AF 
> > deck (it provides audio to the AF deck).
> > 
> > ----- Original Message -----
> > From: "n4buq at knology.net" <n4buq at knology.net>
> > Date: Tuesday, March 7, 2006 9:12 am
> > Subject: Re: [R-390] A bit more on my IF deck
> > To: R-390 at mailman.qth.net
> > 
> > > Okay, I think I'm carrying on a conversation with myself here, 
> but 
> > > I'll 
> > > continue...
> > > 
> > > When I pull the main connector from the IF deck, the 
> resistance at 
> > > Pin 6 of 
> > > V506 goes very close to 500K (what the book says it should 
> be).  
> > > If I 
> > > reconnect the IF connector and unplug the RF deck connector, 
> the 
> > > same 
> > > thing: 500K.  So, I checked the resistance at pin "E" of the 
> RF 
> > > deck (the 
> > > point where Pin 6 of V506 connects to the RF deck).  I get 
> about 
> > > 1.8M 
> > > here.  Those two resistances in parallel yeild what I'm seeing 
> at 
> > > Pin 6 of 
> > > V506 when everything is connected.
> > > 
> > > I haven't traced it out, but I assume if I'm supposed to be 
> seeing 
> > > 500K at 
> > > Pin 6 of V506, then the resistance at Pin "E" on the RF deck 
> > > should be 
> > > nearly infinite.  Any comments on this?
> > > 
> > > Barry - N4BUQ
> > > 
> > > > I got the resistors replaced and all seems fine.  I need to 
> do a 
> > > full IF
> > > > alignment, but it seems to be behaving just a slight bit 
> better. 
> > > I'm not
> > > > sure, but I think it doesn't take quite as long for the 
> system 
> > > to dump the
> > > > charge from SLOW AGC as it did.  Is that perhaps a function 
> of 
> > > that 2.7M
> > > > resistor?
> > > > 
> > > > I wanted to check the resistances and voltages around where 
> I 
> > > had worked.
> > > > Everything looks pretty good except for pin 2 of V506.  
> > > According to the
> > > > manual, I should have about -0.4V, but I'm getting nothing 
> > > (HP410B used
> > > > here).  Checking the resistance, the manual states I should 
> be 
> > > seeing 500K
> > > > in AGC mode and I'm only seeing 400K here.  There are three 
> > > resistors to 
> > > GND
> > > > from V506, pin 2 and they add up to 500K.  Apparently I have 
> > > something 
> > > else
> > > > parallel to this that's pulling the resistance down a bit.  
> It's 
> > > always> something.  Any guesses why I don't see -0.4V here?
> > > > 
> > > > Thanks,
> > > > 
> > > > Barry - N4BUQ
> > > > 
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