SB-401

[Glen Zook]

The "fix" to stop this action in the Collins KWM-2 series is to add a diode (i.e. 1N4007) in the screen connection to the 6146 final amplifier tubes.  There was an official Collins Service Bulletin on this.  Supposedly this fix is recommended for the Heath HW-10X series and the Heath SB-10X series.  Should would fine in the SB-40X series.

The problem is caused by secondary emission from the 6146 screens.

Glen, K9STH

Website:  http://k9sth.com


--- On Tue, 8/17/10, Kenneth G. Gordon <kgordon2006 at VERIZON.NET> wrote:

As I remember it, something very similar occurs in the SB/HW transceivers when the final amp tubes get gassy or exhibit grid emission (or something like that). This is caused in THAT case by something weird in the screen circuitry. It can be fixed by adding one wire to the switching relay which grounds the final amp screens when in the receive mode.
 
I know this sounds strange, but it is mentioned in a Heathkit service bulletin.


      

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