[Amps] re: EBS at soft or quiet moments

[wb8jkr at juno.com]

 There is a way to clean up EBS circuits, I did it a number of
years ago and have never once had comment that the improvement
isn't short of spectacular. I have a 4CX250B 2 meter amp I built
a number of years ago that uses EBS due to the fact that the tube
idles at near full dissipation. I get great reports on the signal
even with relatively close in stations, and I can switch the
EBS in and out of circuit for comparison.
 At any rate, all you need to do is install a 5-10 ufd 100-150
volt electrolytic capacitor across the bias swtiching transistor.
 When cathode current begins to flow the charging of the capacitor
will provide a path for current flow just long enough for the switching
transistor to saturate. Sounds simple as hell, but I can tell you it
works
quite well. 

73,  Mark  WB8JKR


On Thu, 31 Jul 2003 16:18:09 -0700 skipp isaham <nospam4me at juno.com>
writes:
> Are EBS circuits worthwhile..? 
> -
> I would venture to say there is little time where a 
> radio driving an amplifier (combination) has no 
> RF output in the transmit mode. Even quiet station 
> transceivers have a minimal amount of RF output 
> result from ambient room noise. 
> -
> Add some compression and the story gets 
> worse. 
> - 
> The last Alpha EBS circuit I tested, required less than 
> a watt to activate ("trigger"). 
> -
> (The standby/receive mode of a standard amplifier 
> most often cuts off the cathode current, as does 
> the EBS type circuit )
> -
> As quiet as I can be, my peak reading watt meter 
> and scope often indicate some RF output most 
> of the time... even between words on breath and 
> room noise.  Is the EBS honestly helping much 
> in linear mode operation when the input rarely 
> falls below the control detector threshold in a 
> typical amateur operation?  
> -
> I can see the case for CW operation, but 
> most SSB operators are going to bias on 
> during most any portion of the transmit 
> mode where the EBS is supposed to 
> pay off..? 
> - 
> What might I be overlooking...?
> -
> skipp
> - 
> From: 2 <2 at vc.net>
> ***  With no input RF, there is always zero RF circulating current, 
> no 
> matter what type of bias switch is used.
> --  .  When SSB RF drive  drops below the EB-switch threshold level 
> during soft-syllables, the amplifier switches in and out of 
> non-linear 
> bias.  This results in more IMD during soft-syllables.  Another 
> problem 
> with RF-actuated bias switching is that there is no headstart for 
> the 
> amplifier's RF relay contacts to close before RF arrives.  This 
> results 
> in hot-switching the RF input relay and the RF output relay in the 
> amplifier.  For AM and FM modes, RF-actuated bias switching does not 
> 
> switch during soft-syllables, so there is no added IMD, although the 
> 
> hot-switching problem still exists.  
> >
> >Thanks!
> >
> >            ***dan, K6IF
> 
> Rich, AG6K, 805-386-3734, www.somis.org / new e-mail adr r at somis.org
> 
> 
> 
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