[Elecraft] K3 Ground Loop Issues using Ameritron ARB-704

[Paul Christensen]

> "First, to be code compliant, any amplifier that has a neutral
REQUIRES a four wire power cord (hot-Neutral-hot plus ground).
The neutral must be isolated from the chassis (safety ground)
and must be returned to the source (breaker panel) separately.
The neutral may not be tied to the amplifier chassis."

The schematics for both the Ameritron AL-82 and Heathkit SB-200 amplifiers 
show that no neutral is used, regardless of primary voltage setting.  Amps 
that utilize a neutral (e.g., ETO/Alpha 77 series & older Henry) make use of 
a neutral only to power the 120 VAC blower.  These amps require 4-wire 
electrical service as W4TV states.  They were designed and manufactured at a 
time when little attention was paid to the ground v. neutral wiring 
structure.   A fault as a result of a neutral loss between the amp and 
service panel causes the chassis to carry the full blower current.  Anything 
on the amp chassis that's grounded (e.g., SO-239, BNC, RCA) including a 
grounded operator touching the amp will complete the current path.

Most amps do not utilize a neutral and use a jumpered center-tap transformer 
primary to ensure that the amp's blower or fan works correctly on both 120 
VAC and 240 VAC circuits.

Paul, W9AC