[R-390] Call for measurements - 100dB carrier reading

[David Wise]

Thanks, Graham, that's an embarrassment of riches!
Correct me if I'm wrong: you are always injecting
signal on J513, and the "RF Deck unplugged" group
was taken with P108 unplugged.  That will change
the IF readings only insofar as the load on B+ and
the AGC line changes.

My comparable reading was

With RF Deck CONNECTED:
Function switch to AGC

100mV, Diode load -10.0, AGC -13.9

With RF deck CONNECTED:
Function switch to MGC

150uV, Diode load -7.0v

My low diode output suggests that I have a flat
6AK6 or other trouble in that vicinity, and it has
led me to set my IF gain higher than yours.  I will
take a new measurement tonight with IF gain set
so my "AGC link open" readings match yours.
Could you do one more reading group along those
lines, but not only with the link open, but with
the downstream terminal grounded, to ensure that
the grid returns are actually at 0V?  I'll take
a reading and measure the grid returns too, with
a nonloading meter. (Fluke 895A or 877A Differential
Voltmeter, or Fluke 8600A DMM on 0.2V or 2V DC ranges.)

But this is a side issue; my low diode output does not
explain why my AGC is more than yours when I run with my
IF gain turned down for optimum S/N.

Here are this morning's readings, but first a correction
to yesterday.  In the 3rd Mixer column, I had "R215 2.33K".
That should be R218.

1st IF
R501 21.9K
R504 670
R505 29.6K
R506 22.9K
R508 2.29K

2nd IF
R507 21.7K
R513 113
R514 73K
R515 24K
R521 2.12K

3rd IF
R516 22.5K
R518+R519 530 (4K for optimum S/N)
R550 77K
R520 27K
R551 2.15K

R514, R515, R550, and R520 require a "guarded" measurement,
where you elevate B+ to match the ohmmeter output so that
the only current is through the resistor being measured.
(Some bench DMMs have provision to do this automatically.)
Everything is more or less within spec except R504, which
is high or low depending on my deck's mod level.

Dave

> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Graham Baxter
> Sent: Friday, August 24, 2007 4:55 AM
> To: r-390 at mailman.qth.net
> Subject: [R-390] Call for measurements - 100dB carrier reading
> 
> 
> It looks like my attempt to format those results as a table has been a
> total disaster.
> 
> I'll try again
> 
> 4kHz IF bandwidth, RF gain control fully clockwise, IF gain 
> set to -7v at 150uV
> 
> With RF deck UNPLUGGED
> Function switch to AGC
> 
> 150uv, Diode load -5.6v, AGC -450mV
> 1 mV, Diode load -6.9v, AGC -3.3v
> 10mV, Diode load -8.5v, AGC -7.5v
> 100mV, Diode load -11.3, AGC -13.6
> 
> 
> With RF deck CONNECTED:
> Function switch to AGC
> 
> 150uv, Diode load -5.6v, AGC -289mV
> 1 mV, Diode load -7.9v, AGC -2.95v
> 10mV, Diode load -9.9, AGC -6.9v
> 100mV, Diode load -13.5, AGC -12.8
> 
> With RF deck CONNECTED:
> Function switch to MGC
> 
> 150uV, Diode load -7.0v
> 1mV , Diode load -44v
> 10mV, Diode load -103v
> 100mV, Diode load -79v, overloaded
> 
> With RF deck CONNECTED:
> Function switch to AGC
> AGC rear panel link open
> 
> 150uV, AGC -1.3v
> 300uV, AGC -14.5v
> 1mV, AGC -29.1v
> 
> Graham
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