[ARC5] Scott receiver

[Richard Knoppow]

    There are two kinds of bathtub caps, paper and electrolytic. Neither 
has infinite life. The oil filled paper caps used in the RCA AR-88 are 
quite well sealed from atmospheric moisture so have a long life but in 
mine the seals around the terminals disintegrated allowing the oil to 
leak out into the chassis. I did not attempt to restuff them, I replaced 
them with modern plastic caps mostly mounted on terminal strips in place 
of the bathtubs. Some were mounted point to point where that makes 
sense. The AR-88  has no electrolytic caps in it. I replaced all the 
bathtub caps and other paper caps (some were Micamold, used in place of 
the original RCA mica caps) except the triple filter cap which had not 
leaked and seems to be OK.
    The other bathtub caps, as found in many different receivers such as 
the SP-600-JX, are electrolytics. These, like most electrolytic caps 
have limited life. Again, where I have found they needed to be replaced 
I used modern caps mounted on terminal strips.
    Both type of caps are messy to restuff. The oil filled kind may have 
PCB containing oil but also have wax in them. The electrolytic type are 
usually potted in the mixture of resins. You must melt it out. Its bad 
smelling and messy. Getting the covers unsoldered from the cases 
requires a lot of heat applied over most of the seam simuntaneously. I 
have not found a good method for this. A very large soldering iron of 
the sort made for plumbers will work with some care. Some use a gas 
torch like a Bernzomatic. Nonetheless, many rebuilders seem to find it 
worth while to do restuffing and do it successfully. I am more 
interested in function than form and find it a lot of unpleasant work to 
restuff these. I have the same opinion about can type electrolytics 
although they are easier to restuff. One can buy new can caps for many 
applications.
    The reason for both types of bathtub caps was the idea that sealing 
moisture out would extend the life. It seems to always been understood 
that both electrolytic and paper caps had a limited life.

On 11/3/2017 12:08 PM, Kenneth G. Gordon wrote:
> On 2 Nov 2017 at 19:46, Jim Haynes wrote:
> 
>> I recently acquired an RCH also.  Waiting to find time to deal with all
>> the leaky caps.
> 
> Yes. Same here. Seems like ALL the "bathtub" caps in those things go bad.
> 
> Ken W7EKB
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL