[ARC5] ARC-2 Information

[Robert Nickels]

On 9/6/2020 8:08 PM, Hubert Miller wrote:
> ONE ham rig did, I think SBE-13. I have one somewhere. Had a safety indicator lamp on front panel.

Close, but it was on the back panel ;-)   The SBE SB-34 used a 
transformer isolated power supply for filaments, low voltage DC for the 
solid state circuitry, and for bias.   Since the only thing that 
required HV was the driver and two PA tubes, that section of the 
transceiver was "floated" above chassis ground for DC and bypassed to it 
for RF.   The non-isolated voltage tripler ran directly from the AC 
mains but there was no connection to the chassis so there was no chance 
of a shock hazard.   However the radio had a 2 wire cord and plug so the 
intent of the indicator was to make sure it the prong of the plug that 
went to the floating ground was on the neutral side of the line, and the 
hot side would then go to the input of the tripler.  As the manual 
noted, reversing the plug won't cause a shock hazard and the radio will 
work correctly, but some AC hum might be superimposed by having the hot 
side of the line connected to the return side of the floating power 
supply, so if the indicator lit, you just reversed the plug.   They also 
specified a separate safety ground wire to a water pipe, etc., in those 
pre-3-wire days.    It was a pretty clever way to reduce the size and 
weight of a transceiver but SBE must have tired of trying to convince 
people of that as the SB-34 came out soon thereafter with a fully 
isolated supply.

When I converted an All American Five radio into a 75 meter AM 
transmitter/receiver I ripped out the floating grounds and connected all 
the "grounded" things directly to the metal chassis, and then powered it 
from a permanently wired isolation transformer.   That way my 
transmitter could follow usual wiring practices without any worries 
about safety.

73, Bob W9RAN