Forgot to mention the bias. I don't know what the ZSAC (idle plate current)
should be on that tube but it sound in the ball park. Usually idle current
will be around 1/3 of full plate current +- depending on the tube.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of KB0NLY
> Sent: Friday, March 06, 2009 11:34 AM
> To: amps@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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