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@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@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@somis.org
>
>
>
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