[Boatanchors] RCA AR-88 problems

[Bill Cromwell]

On 06/04/2013 04:05 PM, Richard Knoppow wrote:
>    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

Hi,

I'm not one hundred percent sure that you actually have oscillation but 
seems the only way you would KNOW the frequency of the 'regeneration' 
changes if you touch the tube. My first supect is the screen bypass but 
could be other places. I'm voting with Dave. Go over every ground 
connection - screws and nuts, solder connections, etc. Every one. That 
tamed most of the problems in several radios for me.

73,

Bill  KU8H