[AMPS] Bias for SB-220

[Peter Chadwick]

Rich says;

>However, with RF-derived bias switching, the tubes rapidly switch in and
out >of linear bias during normal speech when the relays are in the transmit
>position

Do I understand from that comment that the majority of these bias schemes
actually try to switch to follow the RF envelope, rather than 'hang' for a
few tens to hundreds of milliseconds after the RF disappears? If that's the
case, I can understand why they are so bad for splatter. Given even a
hundred milliseconds hang time, it should be OK for splatter (provided the
attack is fast enough), but without.......................Rich is too kind
in his comments.

73

Peter G3RZP

> ----------
> From: 	Rich Measures[SMTP:measures@vc.net]
> Sent: 	02 June 1999 01:33
> To: 	Pete Smith; amps@contesting.com
> Subject: 	Re: [AMPS] Bias for SB-220
> 
> 
> 
> 
> >
> >OK, I'm confused.  I'm building an electronic bias switch and vacuum
> relay
> >QSK into my SB-220, having finally been jarred out of procrastination by
> >the failure of the changeover relay this past weekend.  In the process, I
> >have become aware of (apparently) wide variation in the bias voltages
> that
> >various modifiers recommend.
> >
> ?  The ZSAC (zero signal anode current) matters more than the actual bias 
> voltage.  In a 3-500Z, IMD goes up rapidly with a ZSAC  of less than 
> 65mA,  I like to use between 75 and 100mA,  
> -  If an electronic bias switch is always in sync with the RF relays, the 
> tubes will always be biased for linear operation whenever the relays are 
> in the transmit position.  (see Fig 7 on my Web site)  However, with 
> RF-derived bias switching, the tubes rapidly switch in and out of linear 
> bias during normal speech when the relays are in the transmit position.  
> This causes additional distortion during soft syllables and at the 
> beginning of syllables.  .  
> >......
> 
> 
> Rich...
> 
> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  
> 
> 
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