[Boatanchors] Micamold Recovery - ENOUGH!!!

[Richard Knoppow]

-----Original Message-----
>From: Rob Atkinson <ranchorobbo at gmail.com>
>Sent: Jun 4, 2014 5:12 PM
>To: Richard Knoppow <1oldlens1 at ix.netcom.com>
>Cc: Jim Wilhite <w5jo at brightok.net>, Boat Anchors List <boatanchors at mailman.qth.net>
>Subject: Re: [Boatanchors] Micamold Recovery - ENOUGH!!!
>
>Thanks for that link Richard.  Too bad the guy replaced the 3 in 1 oil
>cap unit with electrolytics.
>
>Rob
>K5UJ
>
>On Wed, Jun 4, 2014 at 6:43 PM, Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:
>
>>>
>>     I mentioned that the Micamold caps in the AR-88 were used in place of RCA caps that I thought were micas.  I found a web site where one is shown cracked apart. Its called a Micamold but is one of the RCA caps. Down toward the bottom of the page.
>>
>> http://www3.telus.net/radiomuseum/projects/RCAAR88/index.html
>>
     He also seems to have them right out in the breeze.  RCA designed the AR-88 without any electrolytic caps in it. I think this is the main reason for the back-biasing arrangement for the audio, no cathode bypass is needed.  Originally, before WW-2 shortages, all the caps were either oil filled paper or mica except for the ceramic temperature compensating caps.  All of these were the best quality available at the time. I think its possible to get plastic caps of similar capacitance and voltage to the original filter caps. Not sure how expensive they are.  I don't know how they would be mounted. The original filter cap appears to be welded closed and is full of oil.  The newer caps might be small enough to fit under the chassis.  In the very late receivers RCA went to separate caps, two on top and one under the chassis. I think they may also have used electrolytics in some of the low production late models but am not sure. 
     In general its interesting to see how receivers like the AR-88 family and the Navy RAL and RBK were constructed.  While I doubt if these were entirely "cost no object" designs they certainly did not suffer from the usual cost cutting of commercial equipment that must meet a market price.