[Amps] Bias or Plate voltage change

[Vic K2VCO]

GGLL wrote:
> 	Many thanks for the answers. A last question I have is, which is the correct
> CW bias so?, beyond cutoff bias, or just one which makes circulate a slight
> plate current?.

If the bias is beyond cutoff, it will tend to sharpen the edges of 
keying elements.  Depending on how high the bias is and how sharp the 
keying from the exciter (for example an unmodified FT1000MP is VERY 
sharp), you may find that you are introducing key clicks.

Bias close to cutoff establishes class B conditions.  As you increase 
the bias, you approach class C.  In addition to key clicks, class C 
operation will increase harmonic generation which may cause VHF TVI.  On 
the other hand, you will see increased efficiency.

Before the days of SSB, everyone used class C amplifiers for CW.  It was 
common practice to use a lowpass filter after the amplifier to kill the 
VHF harmonics.  Well-built amplifiers of that day were also very well 
shielded to prevent harmonics from bypassing the filter.  Various 
techniques were needed to prevent clicks, such as exaggerating the 
shaping in the exciter, adding a time constant to clamp-tube circuitry, etc.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco