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

[n4buq at knology.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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> 
>