[ARC5] Hallicrafters S-38 is dangerous

[Richard Knoppow]

     In fact I have owned and worked on several S-38 receivers and am 
very familiar with the way they are constructed. You, on the other hand, 
do not appear to have read what I wrote because I confirm the 
possibility of a dangerous condition in receivers with old capacitors.  
Its easy enough to check the caps and the leakage from power line to 
chassis or to cabinet.  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.

On 11/17/2015 9:09 AM, J Mcvey wrote:
>  Obviously, Richard, you have never taken one of these apart. Don't 
> know why you are denying the hazard, but to each his own...
>
>
>
> On Tuesday, November 17, 2015 8:51 AM, Richard Knoppow 
> <1oldlens1 at ix.netcom.com> wrote:
>
>
>     The S-38 has a metal chassis on which the electronics is located.
> This chassis is contained in an external metal cabinet. The chassis is
> isolated from the cabinet by mounting it on insulators and using non
> conductive shafts for the tuning control and shafts for the other
> controls which are not connected to the chassis. In order to bring the
> cabinet to RF ground it is connected to the chassis through a single
> capacitor. If this capacitor shorts or partially shorts (high leakage)
> it will bring the cabinet to the same power frequency potential as the
> chassis. If the plug is connected so that the "hot" side of the power
> line is connected to the ground side the entire cabinet can be at power
> line potential with reference to anything that is grounded.  Also, in
> older power systems the "neutral" side of the line is not always at
> ground potential so even if the neutral and not the "hot" side of the
> line is connected to the chassis the cabinet can have a considerable
> voltage with reference to something that goes to an independent ground
> such as a cold water pipe or radiator. The paper capacitors are getting
> old and old paper caps become leaky.  Shorted paper caps are not very
> usual but this cap is exposed to power line transients so it could
> become damaged under some circumstances.
>     Even when the set is used on DC there can be a danger since the
> negative line is not always at ground potential.
>     The antenna ground connection is also connected to the chassis
> through a paper capacitor so this screw terminal can be at chassis
> potential for power if the cap goes bad.
>     In cheap broadcast receivers the cabinet is usually wood or plastic
> so there is danger only if the back of the cabinet is open (often the
> case) and one touches the chassis and something else that is grounded.
>
> On 11/17/2015 1:34 AM, hwhall at compuserve.com 
> <mailto:hwhall at compuserve.com> wrote:
> > Those old wax/paper caps are electrically leaky and couple the "hot 
> chassis" B- buss to
> > the metal cabinet. If it shorts, the cabinet could have the full mains
> > potential. Bad things can happen...
> > I'm getting confused maybe. Are y'all using 'chassis' and 'cabinet' 
> words the same? IIRC from when I safed my S-38E, one side of the line 
> cord via the on-off switch connected to the B- buss & the buss was cap 
> (& resistor in parallel) coupled to the chassis but the chassis was 
> insulated from the cabinet by non conductive fittings so that the 
> metal cabinet was floating.
> >
> >
> >
> > Wayne
> > WB4OGM
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> -- 
> Richard Knoppow
> 1oldlens1 at ix.netcom.com <mailto:1oldlens1 at ix.netcom.com>
> WB6KBL
>
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL