[R-390] FW: Today's Local & Line experiments

[Craig Heaton]

Testing is done for the day. Checking the grid leak bias goes as follows:

E209 = -7.5VDC
E210 = -6.22VDC
E211 = -3.74VDC
E402 = -0.22VDC

Might add the signal generator had to be connected and was set @ -60dBM
-6.38VDC for these readings. Checked at several input levels and not much
change. Only item out of spec was E402. Don't think the audio issue is here.

BUT:

I ran through the AGC resistance check again with a twist. So with the
function switch in AGC, line unplugged. Terminal #4 to ground on TB102,
resistance is 1.8M ohms. Now with P112 unplugged (goes to IF) resistance
stays the same. Put P112 back on and remove P208 (think that's correct)
which goes to the RF section and carries the AGC line. Result is the
resistance goes to infinity. 

There seems to be a string of 5000pf 1KV caps on that line to ground.

What say??

Craig,
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-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Craig Heaton
Sent: Tuesday, December 31, 2013 12:22 PM
To: r-390 at mailman.qth.net
Subject: [R-390] Today's Local & Line experiments

With quartz55's (Dave) e-mail today, I'll follow his lead and my numbers. 

One micro-volts resulted in or about -0.58VDC on TB102, 3&4

-110dBm = -0.58VDC TB102, 3&4 = 0 on the carrier meter
-100 = -.961 = 10
-90  = -2.29 = 20
-80 = -3.75 = 35
-70 = -5.12 = 45
-60 = -6.38 = 52
-50 = -7.74 = 62
-40 = -9.21 = 70
-30 = -10.66 = 80
-20 = -12.05 = 90
-10 = -13.29 = 95
0 = =14.77 = 100

Measurement were made with a HP 8640B & Fluke 27/FM. No fancy stickers
traceable to NIST

With the jumper disconnected on TB102 3&4, the resistance to ground at 3 was
534K ohms, 4 was 1.82M ohms. Measurement made with Fluke 27.

Then for grins & giggles, the AGC voltage test on the grids of tubes
connected to said line follows.

I used and old ratshack dual FET analog meter to monitor TB102 3&4 with the
jumper in place. The Fluke 27 was used for the grid measurement.

The IF section; V501 thru V503 was consistent. The meter on 3&4 was at
-6.3VDC using the above -60dBM setting. All the tubes in the IF section read
at or very near -6.3VDC using a tube extender and checking the voltage at
the grid with the Fluke 27.

The RF section might be the dirty fly in the ointment??? Once again the
ratshack meter on 3&4 with the HP 8640B cranked up for a reading of about
-6.3VDC. The Fluke was used to measure the grids. NOTE: both meters dipped
to about the  same voltage.  

V201 E208  -3.47VDC
V202 E209  -5.68VDC
V203 E210  -2.6VDC
V204 E211  -2.6VDC

I need to check the above once again with the Function switch in Standby and
check grid leak voltages: per Y2K section 5 pg 5-12.

Happy New Year
Craig

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