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Af-68 Bias from M-1070




 
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Author Topic: Af-68 Bias from M-1070  (Read 3246 times)
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NJ2MR
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« on: April 04, 2012, 06:44:23 PM »

What do you guys think of this Bias curcuit

* BIAS FOR MULTI ELMAC AF-68.doc (51 KB - downloaded 453 times.)
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K3ZS
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« Reply #1 on: April 05, 2012, 08:35:27 AM »

Other methods shown for the AF-67 are simpler and do not require an extra power wire.   The one I use is to place a 5W/22V Zener in series with the modulator tubes (which are now grounded) and then ground the center tap of the driver transformer.   Theoretically this reduces the driving voltage of the modulator but I find with this method, there is still more than enough modulation.  Search this board for AF-67 mods.   There are other ideas.
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K3ZS
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« Reply #2 on: April 05, 2012, 10:35:06 AM »

To clarify, put the zener in series with the modulator tube cathodes, back biased.   I also have the zener bypassed, I think around a 0.1 uF cap.
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