[Elecraft] K3 Key Clicks

[Jim Brown]

On 1/29/2013 4:45 PM, w1gd at aol.com wrote:
> I need help fixing this key click problem before I can take the K3 to a multi-op station.

Hmmm. I've never heard of a K3 causing clicks, but I guess it might if 
something broke.  Don't rule out amplifier bias as the cause of the 
problem at W2GD. W8JI, who has designed a lot of power amps, made the 
following post to the Topband list this morning. Based on what he's 
heard on the air from certain Acom amps, he suspects that they have this 
problem.  On the NCCC list today, N6RK noted that he had to fix a 
similar issue with an Intech amp.

73, Jim K9YC

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If your amplifier uses automatic bias, it can cause clicks. There are 
two things that will prevent or minimize this.

1.) Any auto bias system should not fully cut the tubes off. The tubes 
should stay very slightly into conduction, very near class B but 
slightly on the AB side of B. (B is exactly zero idle current, AB is any 
amount of idle current)

2.) The bias system should be fast on with a hang time on off. It should 
activate much faster than the envelope rise time, and deactivate slower 
than the fall time.

3.) The bias system should activate with almost zero power. Even -30 dB 
background noise on SSB mode should turn on the bias. If it sounds 
choppy on SSB, it is certainly messing up the CW signals.

A good test is to go to SSB mode with constant room background noise and 
gradually turn up mic gain while watching the plate current meter. With 
a 100 watt drive requirement auto bias should fully activate at 10 
milliwatts drive (0.7 volts RMS input drive voltage). This is the type 
of power level we are used to from signal generators, not transmitters.

The AL80B, for example, activates the operating bias with ONE milliwatt 
of RF power. This prevents the amplifier from changing the rise time of 
CW envelopes. Some amplifiers activate much higher levels, and this will 
cause keying artifacts that are as K9YC describes.

Anyone using auto bias and getting complaints should read this:

http://www.w8ji.com/electronic_bias.htm

Having a K3 does not make all signals clean, and not having one does not 
make all signals dirty. It is the entire system that matters, and there 
is certainly more than one clean radio in the world.

73 Tom