[Boatanchors] RCA AR-88 problems

[mac]

Richard,

I've had an AR88/USN RDQ for something like 30 years now.  Not "mint"  
at the beginning by any means and I've had to dig into it several  
times over the years.  Finally did a full re-cap about 3 years ago  
when the seals on the bath tubs started to let go big time.  Did away  
with most of the long leads necessitated by the placement of the  
bathtubs around the periphery of the chassis by mounting the new  
components directly on the screen and cathode pins of the relevant  
tube sockets, transformer and coil lugs, etc., with excellent results.

Have not experienced instability of the kind you report either prior  
to or following any of my forays into the radio, and have not given  
any  particular attention to grounding considerations along the way  
but Dave's points are well taken.  Your observation concerning changes  
when the (presumably metal) second RF and  mixer tubes are touched  
certainly suggests ground related issues.  You might take a big iron  
and try soldering the grounding points in that corner of the radio  
directly to the chassis as opposed to depending on bolts and star  
washers and see if that helps.

Good luck....

Dennis D.  W7QHO
Glendale, CA

***********
On Jun 4, 2013, at 1:05 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
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