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

[Joe Subich, W4TV]

> The schematics for both the Ameritron AL-82 and Heathkit 
> SB-200 amplifiers show that no neutral is used, regardless 
> of primary voltage setting. 

Unfortunately, the AL-82 and SB-200 both create a pseudo-neutral 
by placing high voltage bypass capacitors from each line to the 
chassis/ground.  Unless the chassis is properly grounded to the 
station common point ground along with every other piece of 
equipment in the shack, the noise (hum) s still going to appear 
in common mode on the shields/cases. 

73, 

   ... Joe, W4TV 
  


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Paul 
> Christensen
> Sent: Thursday, June 04, 2009 3:06 PM
> To: Elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 Ground Loop Issues using Ameritron ARB-704
> 
> 
> > "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
> 
> 
> 
> 
> 
> 
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html