[R-390] Re: Image Problem

[Tony Casorso]

I'm losing track now :). I'm no longer positive where the sig gen was. I 
tried it so many ways. I have checked the AGC before against the curve in 
the manual and it is pretty close. You could pick off -4.2 volts on the 
curve and have some idea what I was applying at that time.

Tony

----- Original Message ----- 
From: <SHELLY199 at aol.com>
To: <r-390 at mailman.qth.net>
Sent: Sunday, October 21, 2007 2:58 PM
Subject: [R-390] Re: Image Problem


>
> Tony,
>
> When you measured the  voltages below what was the gen input voltage?
>
> Voltages are
>
> With  no AGC applied:
> Plate 201v
> screen 178v
> cathode 2.1v
> grid  -.5v
>
> With AGC applied:
> Plate 215v
> screen 201v
> cathode  .22v
> grid -4.2v
>
>
> The agc, with the Langford mod, should be  about:
>
> 10 Uv rf input = -4.36 Vdc
> 100Uv rf input = 6.66
> 1000 Uv rf  input = 8.53
>
> I don't know if this will help, but you are talking some  very big rf 
> input
> voltages (20mv).
>
> I also had a problem with the Ist rf  amp not responding to the AGC 
> voltage
> once.   Tube tested good and the  agc voltage was there.  Was fixed with
> another rf amp tube.  That took  a lot of work.
>
> By the way, if you use In914 or In4148 diodes in that  Langford mod I've
> found that one of the diodes will fail.  I use  1n5060.  I think it's 
> breakdown
> when the AGC switch is turned from slow to  medium. This has happened in 
> at
> least 5 IF decks.
>
> Rich WD2Q
>
>
>
>
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