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[AMPS] Bias for SB-220

To: <amps@contesting.com>
Subject: [AMPS] Bias for SB-220
From: measures@vc.net (Rich Measures)
Date: Wed, 2 Jun 1999 09:50:35 -0700


>
>First, RF bias switching does not cause problems when properly 
>implemented. So that is a non-issue.
>
?  I continue to hear amplifiers with the problem, Tom.  When can proper 
implementation be explected?

>Second, while Rich focuses on the electronic bias with  empirical 
>conclusions many rigs have horrid leading edge distortion.

?   Leading edge distortion occurs during ALC attack.   Leading edge 
distortion can be considerable if the operator insists on running the 
microphone-gain control at levels that produce high ALC readings.  
However, if microphone-gain is reduced to a level that produces little 
ALC indication, overshoot is minimal.  
>
>..........
>The key to successful auto-bias is NOT pulling the tubes up into 
>cutoff, but letting them rest at low dissipation on the class AB side 
>of B.
>
>The second key is a bias switch that actuates at milliwatt power 
>levels, and that has a response time many times faster than the  
>rate of the fastest envelope rise time permitted.
>
?  Does it make good engineering sense to wait for RF to start arriving 
at the amplifier before beginning the switch to linear-bias?  By 
syncronizing the EBS with the relays, linear-bias is applied several 
milliseconds before  RF-arrival.  .  This is how the high speed switching 
circuit in Fig. 7 works.  (Fig. 7 is on my Web site) 
-  later



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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