On 1/29/2013 4:45 PM, [email protected] 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
= = = = = = = = = = = =
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
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