The electronic bias switch circuit may cause additional IMD during soft
syllables, but in normal Ameritron amplifiers it does not cause any hot
switching of T-R relays because the amplifier remains "keyed" as long as the
key line signal from the exciter is present. It only switches bias between
"near cutoff" and "operating," but the T-R relay contacts, both exciter and
amp out sides, remain keyed the whole time. -WB2WIK/6
"Success is the ability to go from failure to failure with no loss of
enthusiasm." -Winston Churchill
> -----Original Message-----
> From: 2 [SMTP:2@vc.net]
> Sent: Wednesday, July 30, 2003 2:27 PM
> To: Dan Levin; AMPS
> Subject: Re: [Amps] Ameritron EBS-1 in AL-1200?
>
> >I'm pretty clueless about such matters, and would appreciate any advice.
> >
> >What do folks think about the importance of, and/or utility of,
> installing
> >the
> >EBS-1 electronic bias kit in an AL-1200 that is going to see heavy duty
> >contest use?
> >
> >At the risk of demonstrating to the world my complete lack of
> undestanding
> >of high power amplifiers, is it correct that this kit basically senses
> input
> RF,
> >and biases the tube to cut-off in the absence of input RF - thus reducing
> the
> >"circulating currents"?
>
> *** 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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