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Author Topic: acom 2000A bias optimizer circuit question  (Read 2457 times)
KA7GKN
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Posts: 149




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« on: April 15, 2004, 03:56:14 PM »

Many amps today use some sort of electronic bias circuit claiming it reduces the tube's generation of heat. It does this by biasing the tube on and off..in between words/syllables.

Ok, that's how I understand it.

many folks have disabled their electronic bias circuit not too concerned about excessive heat. this is
to elimiante the biasing anomaly when you start certain words or pause too long between syllables. This anomaly sounds like RF or crunching or like someone crinkling cellophne behind you.

Some amps are: ameritron, alpha, emtron....that have electronic biasing..and have had their biasing modified or disabled.

I'm running the Acom 2000A and have become aware of the similar anomaly with their bias circuit, called "bias optimizer" the amp uses the 4cx800a tetrode grid driven amp. [2 tubes]

Has anyone modified a 2000A to allow I think a faster bias swing to switch the tube off faster between pauses in words. I think this requirees reducing the release time constant of the rc circuit.
-OR- is the opposite correct where the time delay needs to increased so the tube does not go into cut- off during the short pauses between words?

any real experiece of this topic specific to the 2000A is appreciated
please no conjecture replies are necessary [thank you]

Marty  ka7gkn
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W9GB
Member

Posts: 3367




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« Reply #1 on: April 17, 2004, 06:57:55 PM »

Marty -

You may wish to read Risk Measure's web article which talks about: ELECTRONIC CATHODE-BIAS SWITCH [ECBS].
http://www.somis.org/QSK922.html

http://www.somis.org/HSSw.GIF

Greg Ordy's W8WWV web page may also be useful.

It deals with the "upgrade" of his Ameritron AL-1200 electronic bias board.
http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/AL1200.htm


w9gb
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