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

[Barry]

Paydirt.  I think I have some weak/gassy/whatever, tubes.  I swapped V506
with another 5814 in the RF deck and I got about -0.1V at pin 2.  I then
swapped it with one of the other 5814's in the IF deck.  This tube yields
about -0.5V on pin 2.  I seem to recall that gassy tubes can cause low grid
voltages, but not sure about that.  Also, it seems that the radio is a bit
"hotter" with this tube arrangement.

I know Roger created a writeup on swapping tubes for maximum performance.
Maybe I'll give that a look-see.  I didn't put these tubes on the tester
before firing this thing up.  Maybe that will reveal something about them
too (yes, I know the *best* tube tester is the circuit itself, but I want to
see if the Hickock will tell me anything obvious).

Oh well, this has been a fun exercise.

Barry - N4BUQ

----- Original Message -----
From: <n4buq at knology.net>
To: <JMILLER1706 at cfl.rr.com>; <R-390 at mailman.qth.net>
Sent: Tuesday, March 07, 2006 10:44 AM
Subject: Re: [R-390] A bit more on my IF deck


> 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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