[R-390] R-390 Digest, Vol 60, Issue 14
SHELLY199 at aol.com
SHELLY199 at aol.com
Mon Apr 13 14:56:33 EDT 2009
Tony,
The no signal AGC voltages you see are OK. If you have the Langford mod
you'll see it get quieter when going from MGC to AGC. If you turn on the
calibrator and measure AGC you should see approx.-5 to -6 Vdc The Diode Load
voltage should be -3 Vdc with the calibrator on. I just measured a deck
with the Langford mod.:
diode load AGC meter
no signal in MGC -.48 0.0
no signal in AGC -.46 -0.22
Cal on -3.27 -5.8 52
db
If you have the capability to put 150 uv @ 455 KHz into J513 on the IF deck
and adjust the Gain pot for -7 Vdc on there diode load you should see the
above.
Rich
wd2q
n a message dated 4/13/2009 12:01:23 P.M. Eastern Daylight Time,
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Today's Topics:
1. R-390a AGC Issue/Observation (Tony Casorso)
2. Re: FS Items (Dan Arney)
----------------------------------------------------------------------
Message: 1
Date: Sun, 12 Apr 2009 16:39:13 -0600
From: "Tony Casorso" <canthony15 at msn.com>
Subject: [R-390] R-390a AGC Issue/Observation
To: <R-390 at mailman.qth.net>
Message-ID: <BLU0-SMTP159B79311A76ABDAE414EEC97E0 at phx.gbl>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
I have been annoyed for quite a while with the fact that I get a big drop
in
gain when I switch from MGC to AGC, even when tuned to just background
noise.I checked the AGC bus voltage and found that it was about -.9 volts
in
AGC and 0 volts in MGC. I wasn't sure if -.9 was reasonable for the AGC
with
no signal but I suspected that it was not becasue of the big drop in gain
and the fact that this radio is supposed to have delayed AGC.
I first checked the resistors on the IF deck (R544, R545, and R546 if I
remember correctly). They were fine. I also disconnected my 2 diode AGC
mode
(the Lankford mod). That made no difference. I could see a postive voltage
on the plate of the AGC rectifier but negative on the AGC bus. When I
pulled
the AGC time constant tube (V506 which also doubles as the detector), the
AGC bus went to +1.2. That surprised me since it is only the grid of V506a
that is connected to the AGC bus. But we are trying to pull the grid
positive so maybe it makes some sense. Anyway, I swapped the tube with
another 5814a. It was a little better but not much. Still about -.7 volts.
I
stuck in a 12au7a and got about -.3 volts. Finally, I put in a 12ax7a and
the AGC bus stayed near +1.2 volts with no signal. With the 12ax7a in
there,
there radio acts like I expect. On weak signals, switching from AGC to MGC
makes little difference. The radio seems livelier too. I'll have to try it
this way for a while, but I think I like it.
If anybody else is so inclined, I would like to hear what your AGC bus
goes
to with no signal. You can measure it on the back panel so you don't even
need to open it up. Also, I would like to know if you hear a substantial
drop in the background noise when you switch from AGC to MGC with no
signal
present.
My radio is a 1967 EAC with all EAC modules.
Thanks,
Tony
------------------------------
Message: 2
Date: Mon, 13 Apr 2009 10:20:58 -0500
From: Dan Arney <hankarn at pacbell.net>
Subject: Re: [R-390] FS Items
To: milsurplus <milsurplus at mailman.qth.net>, baswaplist at foothill.net,
Old Tube Radios <boatanchors at theporch.com>, R-390 List
<r-390 at mailman.qth.net>
Message-ID: <49E3585A.7090606 at pacbell.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
The following units are to heavy to ship at a reasonable rate so they
are for pickup only in McKinney or delivered to Belton, or Dayton.
The price is net to me certified funds, cash, Paypal or bank wire
transfer to my account PREPAID.
1. Collins 30-S1 Mars version, SN 17XX original manual. This unit looks
like it just came from the factory and it worked fine when removed from
service. Will not be DOA. $3000.00.
2. Ambassador solid walnut operating console on casters.
The panel is cut out for Collins S line for a 75S1, 312B4 and a KWM2 or 2A.
Asking $3000.00 OBRO.
3. Rohde & Schwarze EK-07/D2 strapped for 115V AC checked out clean with
English copy of the manual, 2 wire power plug. Audio plug for speaker,
Coax connector to BNC.
Pick up saves $100.000 crating and packing charge and 200 plus pounds
freight charge.
$2000.00 each I have 5 working units and one condition unknown.
4. R-390-A no meters, with RF deck cover sold as-is no power applied due
to blocking cap for filters not replaced. $450.00 each I have 30 units.
5. R-390-A with original meters details same as above. $525.00. each I
have 15 units
6. R-390-A with meters all EAC modules, CNC Engraved panel, recapped,
frame disassembled and gold alodined, 3 wire power cord, all covers
checked and aligned with 3TF7. $1800.00.
Units are sold on a first come first money.
PICTURES AVAILABLE FOR FOR SERIOUS BUYERS.
Thanks for reading,
Hank
KN6DI
------------------------------
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End of R-390 Digest, Vol 60, Issue 14
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