[ARC5] Hallicrafters S-38 is dangerous

[J Mcvey]

 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 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
WB6KBL

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