[Amps] A Symptom of Low Bias?

[Steve Katz]

What exactly is the amplifier make/model of the amp (or is it homebrew)?

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
Behalf Of KB0NLY
Sent: Friday, March 06, 2009 8:34 AM
To: amps at contesting.com
Subject: [Amps] A Symptom of Low Bias?


Still fighting some small bugs in the new amp this morning, does this sound like a symptom of the bias being too low??

When i key up with no drive the plate idles at about 90-100mA, and the grid goes slightly negative, just enough to pull the needle a hash mark width below the zero on the scale.  As i apply drive the plate comes up to about 400mA and the grid starts to come above zero, but i have to literally YELL on SSB to get the grid to come up and see full output.  I tried some CW on it last night and its making full output there.  Also at the suggestion of some on here i tried applying drive on FM and the grid came up to 100mA and the plate stayed around 400mA yet.

So from the info i can find online, in the handbooks, picking others brains, etc..  It would seem i still have a bias issue here as its only amplifying on the voice peaks on SSB.  I dug through my drawers and didn't have the parts to do the mod for higher bias on the Triode Board so i ordered some zeners from Mouser today and i will get that done when they arrive and see if i can further adjust the bias and get the idle current down some more as well.

What do you guys think??  Starting to realize once again why i like building stuff, learning is fun!

73,

Scott



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