[R-390] Low IF gain problem

[DCrespy@aol.com]

Phil and gang,

The Lankford mod does make the AGC more "aggressive".  That is it takes less 
signal to get the same AGC action.  Very strong signals are reduced more than 
they were before the mod.  Dallas noted this in one of his HSN articles.  It 
is a fairly obvious side effect.

I have done three radios with the mod, and have not experienced the problem 
you describe, however.  The S-meter readings did not change significantly, so 
I do not think it is the mod.  Unless...  My mods have always been done with 
1N4148 switching diodes.  I suspect that rectifier diodes and some older 
general purpose diodes may be a problem.  I have run into this on similar AGC 
mods on the R-388.   Something to check?

73
Harry  KG5LO:


> Subject: [R-390] Low IF gain problem
> 
> Hello All.
> Yesterday I mentioned that I thought the R-390A I'm working on seemed to
> have low gain, though it was hearing weak ones ok (It "hears" my sig
> generator, AM modulated 50% at it's lowest setting of -127dBM just fine).
> However I mentioned I thought the IF gain seemed low as indicated on the
> S meter, so I checked it by inserting 150uV at 455kHz into J513 and tried
> setting the gain control for -7VDC at the diode load jack (per the
> manual).  The highest I can set this for is 5.0VDC and with gain about
> halfway (where I set previous receivers) it reads 2.9VDC in ALL bandwidth
> settings.
> 
> Question.  Does the Lankford AGC mod affect gain any in this IF strip,
> perhaps by loading it down (2 diodes across a couple resistors)?  I've
> tried subbing tubes. 
> 
> 



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