[R-390] 0.5-8.0 Low Sensitivity (Long)

[ToddRoberts2001 at aol.com]

In a message dated 8/16/2006 6:56:44 AM Eastern Standard Time, 
dmartin at visuallink.com writes:
The 1st IF cans are unique in that they do not have any caps >inside< the can 
except 
the trimmers, which means you have to go for a deep dive under the rf deck. 
C281 and 
C282 are two >very low value< coupling caps that join Z213-1 to -2 and Z213-2 
to -3. 
C281 does see B+ and Z213-1 is the only 1st IF can with B+ on its trimmer 
cap. 

Yeah, if you are going to have to pull the rf deck, carefuly replacing all 
five caps 
with proper subs may be the way to go. (Where to find a 1.5 pf with the 
needed 
tolerance, though, and do these funny little "tubular" caps really often go 
bad?)
Let's see how others weigh in on this!

Good advice! On replacing the 1.5pf coupling caps - that value seems to be 
impossible to find nowadays. I would imagine the more common value of 2pf would 
work fine in this application but if someone wanted to be super accurate they 
could use two 3pf caps in series for 1.5pf total.  I see Mouser has both 2pf 
and 3pf 300V rated micas and 3pf 500V micas in their catalog. As you mentioned 
there is B+ across C281 so best to use at least a 300V rated mica cap here. I 
have never seen the coupling caps go bad before but there is always a first 
time and if the radio is acting funny and you have the RF Deck off probably best 
to replace them just to be sure. 73 Todd WD4NGG.