[Boatanchors] RCA AR-88 problems

[Richard Knoppow]

    My AR-88 is a former Navy reciever so it may be on topic 
here. I've renewed this receiver as much as possible. 
Replaced all the bypass caps in it.  The bathtub caps were 
all leaking oil. They were replaced by modern film caps on 
terminal strips. I had no luck trying to restuff the 
original cans. I also replaced the Micamold paper caps in 
the RF compartment with film caps.  Everything works but I 
am getting regeneration on the top three bands. I think this 
is originating in the second RF stage. I have also recently 
had a problem with the plunger trimmers between the second 
RF and mixer going out of range on two bands.  I don't know 
if these are related.  Touching the second RF tube or mixer 
tube moves the points of oscillation around but does not get 
rid of them.  I've resoldered the ground connections to both 
tube sockets. The regeneration varies with RF gain as one 
would expect.  Its obvious that there is feedback but I 
can't figure out where its coming from.  I've tried bridging 
the new film caps in the RF with ceramic caps to no avail. 
Also tried different tubes.
     I am about to see if the trimmers may not be grounding 
completely.  The chassis had a lot of junk on it partly from 
the leaking caps. The trimmers are held on with hex nuts at 
the top and there are solder tabs on the bottom against the 
chassis. Its possible they are not grounding all the way.
     I have been posting on the RCA equipment list but am 
also posting here and on the boatanchor list to see if I can 
get a larger audience.  I need to hear from others who have 
restored AR-88's and might have encountered similar 
problems.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com