[ARC5] Hallicrafters S-38 is dangerous

[hwhall at compuserve.com]

>

Itsprobably a good idea to replace the line bypass caps in these receivers withthe modern ceramic types that fail open.
>

 
There's a family of special caps, known as X and Y types,  made for line bypassing either line-to-line or line-to-chassis. They're supposed to have fail-safe modes. They were recommended by the instructions I was using to safe my S-38E & I picked up a handful at the local surplus store.

Wayne
WB4OGM


-----Original Message-----
From: Richard Knoppow <1oldlens1 at ix.netcom.com>
To: arc5 <arc5 at mailman.qth.net>
Sent: Tue, Nov 17, 2015 2:34 pm
Subject: Re: [ARC5] Hallicrafters S-38 is dangerous


I don't know about the E but the ones with the half moon dials have 
a cord
riveted to the back cover so when you take the cover off there is 
no power. 
Of course, its easy to cheat it and one has to to align the 
IF but RF
adjustments are made through holes in the bottom cover. The OP 
is right, there
is an inherent danger in using an AC/DC supply, but 
considerable protection
can be given by proper design. My disagreement 
was in his saying the S-38 was
badly designed. IMO it was not, at least 
any more so than many consumer
sets.
     BTW, one of the hints in the handbook is to insert the plug for

minimum hum. I suspect there is increased hum when its backward, i.e. 
hot
side of the line on the chassis. Of course, on DC the set just 
doesn't work at
all if the plug is reversed. There was never much DC in 
the U.S., mostly in
New York City in areas once set up by Thomas Edison. 
DC has some advantages
for large motors of the sort used on elevators so 
the system persisted until
about twenty years ago.  A google search 
would probably provide the date.  A
lot of ships also had DC power.  
Some shipboard radio systems used
motor-generators to provide high 
voltage from low voltage DC. National and
some others, made AC/DC 
receivers specifically for use on shipboard.
     Its
probably a good idea to replace the line bypass caps in these 
receivers with
the modern ceramic types that fail open.
     There is an effect where you can
"feel" AC on a cabinet like the 
S-38, feels like a rough surface when you run
your fingers over it.  I 
don't know how much voltage it takes to produce this,
maybe not much.  
The caps DO pass some AC at power frequencies, not much but
maybe enough 
to give this effect.  Some AC only receivers have slightly hot
chassis 
from the RF bypass caps on the power line. Again, they don't pass much

AC at power frequencies but enough to feel.


On 11/17/2015 10:35 AM,
hwhall at compuserve.com wrote:
> I have owned and worked on several S-38
receivers and am
> very familiar with the way they are constructed.
> ...
>
Hallicrafters did what was typical at the time
> to protect the user.  The
chassis can not be
> touched in normal use because there is a back cover
>
with an interlocked power cord.  You need
> a cheater cord to work on the
set.
> I assume that last half was meant to refer only to typical consumer item
construction. The S-38E I have certainly had no interlocked power cord - it
passed directly into the bare chassis (not to be confused with the painted
cabinet). Every old TV I took apart, and some later-model plastic AM-FM sets I
tinkered with, did have an interlock, tough.
>
> Wayne
> WB4OGM
>   
>
>
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-- 
Richard
Knoppow
1oldlens1 at ix.netcom.com
WB6KBL

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