[R-390] No receive below 8 Mc

[Jim M.]

I forgot to answer your other questions. I think if you look at the schematics you will see that the following have fixed tuning caps (usually in combination with a trimmer) INside across primaries:

First mixer Z-213 (these may be outside the cans)
Z-201 through Z-205
Second mixer Z-216 (all)
Third mixer T-208

In the IF module:
AGC amp Z-503
4th IF T-503

To replace caps inside cans, remove slug racks, remove coil covers, clip out the old caps, replace with modern mica caps, and realign.  Other stages/cans have the caps outside the cans. 


Sent from my iPad

On Oct 19, 2016, at 12:38 PM, Barry <n4buq at knology.net> wrote:

>> ... I recently did a shotgun replacement of all primary caps in my SW 390a
>>> and noticed an enormous improvement on all bands.
>> I wonder if by "primary caps, where the primary is in the plate circuit of
>> a stage" you mean bypass caps from the B+ side to ground, or if you mean
>> the cap meant to tune the coil, across the primary.  And, I wonder how many
>> caps were found INside the coil cans.
> 
> I took that to mean the caps in the transformers.  If that was the case, did you check before and after performance for each replacement?  It would be interesting to know if improved performance was due to more than one replacement.
> 
> 73,
> Barry - N4BUQ