[Hallicrafters] Bumblee Caps

[Richard Knoppow]

----- Original Message ----- 
From: <hallicrafterssr2000 at k9axn.com>
To: <hallicrafters at mailman.qth.net>
Sent: Saturday, November 03, 2012 9:11 AM
Subject: [Hallicrafters] Bumblee Caps


> Questions regarding the history of these components.
>
> 1.  Who manufactured the Bumble bee, Black beauty, Black 
> cat, etc
>     capacitors?
>
> 2.  Did General instruments ever make paper caps and when 
> did they
>     start building Polyester caps?
>
> 3.  Does anyone have a good Bumble Bee cap in their 
> possession?
>
> The SX-100 and other early 50Kc I.F. systems used 10% 
> non–inductive (High quality?)Bumble Bee caps on the band 
> width switch.  I have not found a single one of those caps 
> that were within measureable tolerance due to leakage.
>
> Note that the SX-117, HT-44, SR-150, and later radios used 
> General instruments non-inductive Polyester, not paper 
> caps, that are as good today as when they were built. 
> They look like the old paper caps but are not --- they 
> also have the General instruments logo.
>
> One of the most common mistakes when restoring the later 
> radios is to replace all of the paper caps with ceramic 
> disc caps.  Bad move, they are Polyester and stable, not 
> paper, whereas the high K ceramic are unstable, 
> unpredictable and totally inappropriate for these circuit 
> designs.
>
> When replacing the caps on the 50Kc band width switch, use 
> Polypropylene or Polyethylene film not ceramic disc caps. 
> BTW, all of the Hallicrafters radios used non-inductive 
> caps in the 50Kc bandwidth selection circuits.
>
> Kindest regards Jim K9AXN
>

     "Black Beauty" caps and "Telecap" caps were trade marks 
of Sprague Electric Company, a major manufacturer of 
capacitors.  "Bumble Bee" is a fairly recent (with reference 
to the manufacturing period) nick-name for Black Beauty caps 
due to the RMA code striping used on them.  Code striping 
was used on many other caps as well but the black body with 
stripes is distinctive, hense the name.  The Black Beauty 
caps that failed early seem to have been intended to be a 
high-quality cap with good tolarance for high ambient 
temperatures.  They used a plastic coated paper dielectric 
which was impregnated wtih oil and sealed in a Bakelite 
case.  They _should_ have been quite long lived but 
evidently began to fail soon after manufacture.  One reason 
was the method used to fill the cases with oil: one of the 
leads was actually a tube. The tube was used to fill the 
body of the cap and then sealed by placing the lead wire 
into it and soldering.  If excessive heat was applied when 
the cap was installed the seal was broken and the oil would 
slowly leak out.  There may have been other problems as 
well.  Sprague also sold a cap called "Orange Drop" using 
the same dielectric material. These were radial lead caps in 
dipped epoxy cases and evidently did not fail quickly.  The 
"Telecap" (for television capacitor) was again the plastic 
coated paper dielectric but without the oil.  Telecaps were 
black but the values were printed on the body.  These also 
behaved normally for good quality paper caps.  Sprague 
referred to Telecaps as "these black beauties" in later 
advertising I suppose indicating that they could be used for 
the same applications.  BB caps with stripes are found in a 
lot of high end equipment such as General Radio and 
Hewlett-Packard as well as Hammarlund, etc.  The engineers 
of the time must have expected good performance of them.
     I don't know why polypropylene or polyethelyne should 
be superior to ceramic, at least Class-1 ceramics for RF 
use. In general they have excellent RF performance and very 
low inductance.   Most modern film caps have pretty low 
inductance anyway.  Once in a while you will find low 
inductance paper caps with flat braid leads.  Hallicrafters 
among others used them.
     There are instruments which will measure all the 
significant characteristics up to microwave frequencies so 
presumably one could obtain complete RF data on most 
capacitor products.


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