[HCARC] A little nostalgic help please...

[Kerry Sandstrom]

Mack,

I just had a chance to take a look at the schematic.  The cabinet is 
connected to one side of the AC power line through a .25 microfarad 
capacitor.  When the cabinet is not grounded, it will reach the potential of 
the AC power line it is attached to, that is , if that side of the AC line 
is the hot (Black) side, the cabinet will be at 110 VAC.  It won't be able 
to deliver much current , but you can get quite a shock anyway.  Now, if the 
now 65 year old capacitopr has failed and is shorted, the cabinet will be 
directly connected to the AC line and that is lethal.

The ground connector for the antenna, according to the schematic, is 
connected to the chassis through a .01 microfarad capacitor.  The chassis is 
directly connected to one side of the AC line.  Again, if that side by 
chance happens to be the Hot (Black) side, the chassis will be sitting at 
110 VAC relative to ground as will the the antenna ground connection and the 
other antenna connections also.

The chassis must be isolated from the cabinet.  I don't know how 
Hallicrafters did it, but however it was, its also 65 years old.  There were 
probably some insulating bushings for the screws that held the cabinet on. 
If it had been taken apart many times, I bet they are missing.

In high school a friend of mine had an S-38 E, basically an updated 
mechanical design, but the same circuit.  I can remember listening to it 
with no problems, but that was over 50 years ago.

Hallicrafters was noted for making affordable radios that didn't push the 
state of the art like National and Collins and a couple others.  There were 
a lot sold which may account for their popularity. (That is of course my 
personnel opinion!)

Another idea for a safer power supply is a 125 VDC, 250 milliamp DC supply. 
I don't know if that would be any easier to find, however, since the S- 38 
needs 30 Watts AC or DC that should be adequate.  There are two independent 
safety issues: One is you have a radio that has high voltages present and 
two, the cabinet and chassis and antenna are potentially 125 Volts above 
ground.  There is nothing practical you can do about the first safety issue. 
All old vacuum tube radios are like that.  The only practical way to solve 
the second issue is with some kind of isolation transformer between the 
radio and the AC line.

Kerry