[R-390] If alignment and low signal

[n4buq at knology.net]

On Wed, 30 May 2007 09:26:22 -0400, "FISCH, MICHAEL" <mfisch at kent.edu> 
wrote :

> Hi:
>  
> I am finally getting close to completing my R-390a fix up.  Last night I 
was aligning the IF.  I would think when I put 455 kHz into the module (per 
wisdom, etc.) that the voltage on the diode load should be approximately 
independent of bandwidth for 2-16 kHz (thats as far as I am) 16 and 8 kHz 
are close, 4 Hz is about a factor of 4 smaller and 2 kHz an other factor of 
2-4 smaller.  The tunable caps seem to have minimal effect on these last 2 
filters; however, the width of the filters seem about right.  My guess is 
the silver mica caps need to be changed.  Is that the correct diagnosis?  
Also will 500V capacitors work? 
> Thanks
> Mike

While I haven't had to replace those caps, I think that's the general 
recommendation.  You should see two peaks with the trimmers and if you 
don't, the SM caps are either bad or need a different value to make the 
trimmers peak in their ranges.

Good luck with it,

Barry - N4BUQ