John Heck jkh at LEXIS-NEXIS.COM
Thu Feb 19 08:42:59 EST 1998

The original S-38 did indeed have a floating ground. It also had a metal cabinet which was isolated
from the chassis by rubber grommets, and the chassis was coupled to the B- buss via caps for an RF
ground. The later S-38's, however, the S-38B and onwards, also had the isolated chassis, *but* they
had one side of the power cord attached directly to the chassis, thus making it of the "dangerous"
AA5 type. The original poster of this question has an S-38C, if memory serves, so he will need to
be mindful of the polarized line cord suggestion. I checked the schematics for the S-38s last night
and this is born out with them. It would be well to actually do a physical inspection of your own
particular S-38 to determine which wiring technique Hallicrafters actually used *if* you have one of
the original 6 tube S-38s. There was much variation in these about the time of switchover to the S-38B.
For instance, I have a black crackle, six tube(independent BFO), S-38, which uses an S-38 chassis but
is wired as an S-38B in the tuning and IF circuits, with the 160M trimmer and padder missing. This caused
me no end of confusion when I first tried to align this receiver until I realized what I was dealing
John Heck, KC8ETS
1009 Donson Drive
Dayton, Ohio 45429
jkh at lexis-nexis.com

> Hello Rod & list
> 99.9% of the old "AC-DC" sets had what was called a "floating ground";
> the chassis was NOT connected directly to one side of the AC line.
> Rather, there was an isolated "bus" for one side of the AC line and
> minus DC.  This bus was connected to the chassis, usually, through a
> parallel combination of a 470K resistor and .05 (or .047) mfd capacitor
> (values varied somewhat from model to model of set).  This put the
> chassis at RF ground potential, but prevented one's contact with an
> otherwise hot chassis while one was grounded from being an exciting, if
> not lethal, experience.
> Bottom line:  I don't have a schematic of the S-38 in front of me, but
> since the set has a metal cabinet, I'm quite sure that the floating
> ground approach must have been used in its design.  The thing to do is
> locate that cap which connects the floating ground to the chassis and
> replace it with a modern, mylar cap rated at 630 VDC, regardless of
> whether it seems to be leaky or not.  Also check the value of the
> parallel resistor to make sure it hasn't decreased greatly in value
> (rare, but not unheard of).  I would NOT use the Equipment Ground line
> as a power return.
> Ed Greeley
> Mobile, AL

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