[R-390] AGC problems - need help interpreting IF resistance readings

[Dennis Wade]

Thank you everyone for your responses.

The 8 Kc filter had a high resistance (~120K) short to ground.

When I opened up the filter box, I discovered why the 16 kc filter was
out of the circuit..it has about 5K from ground to either terminal. 
And, one side was still wired into the common side of the filters! 
That helped me  discover the hard way that I needed to isolate BOTH
terminals (duh) since one side is all wired in common in order to find
the second suspect filter.  I also discovered that the tabs on the
trimmers will only flex so many times before breaking.  One got flexed
one too many times...luckily it was the one for the 8kc filter.  So, I
put shrink tubing on the exposed wires and hooked up the remaining
working ones and fired her up.  Sure enough, no more distortion on
strong signals, and overall an improvement in audio quality.

Well, if I had to loose 2 filters, I guess those would be the two to
loose (for my listening anyway.)

I don't feel a need to replace those filters right away.  I happen to
have an 8 and 16 kc Clevite ceramic filters, and a 4 kc as well.  I'm
also wondering as I type this if there may be other filter options
which would give me more flexibility.  (note that this particular
'390A has the "factory" SSB mods done on it).  Comments are welcome.

          Thank you all again for your help.

                      Dennis



On 9/5/05, John Kolb <jlkolb at jlkolb.cts.com> wrote:
> At 02:48 PM 9/5/2005, Dennis Wade wrote:
> >Well, I think I've isolated the problem to the output side of the
> >mechanical filter group, so its  either a filter, a mica cap
> >(unlikely, since the filter would have to be leaking to ground too),
> >or the switch itself.
> 
> snip
> 
> >There is no DC path from input to output of a mechanical filter, correct?
> 
> Correct, the input coil will measure somewhere around 50-60 ohms, as
> will the output coil, but infinite between the pair. Also, should be infinite
> between either coil and filter case (out of circuit)
> 
> John
> http://www.jlkolb.cts.com
> 
> 


-- 
Dennis L. Wade
KG6ZI
Carmichael, CA