[Amps] A Symptom of Low Bias?

[KB0NLY]

I was thinking that's a possibility, but I have to figure out yet why that 
Grid meter acts weird like it does.  I don't understand why that meter goes 
to a negative reading with no drive, got any suggestions there?

I'm going to borrow another meter and double check with a known good peak 
reading meter.

73,

Scott


----- Original Message ----- 
From: "Steve Katz" <stevek at jmr.com>
To: "KB0NLY" <kb0nly at mchsi.com>
Cc: <amps at contesting.com>
Sent: Friday, March 06, 2009 1:39 PM
Subject: RE: [Amps] A Symptom of Low Bias?


Are you sure the symptoms described aren't simply the measurement technique?

Unless you use a scope or true PEP output meter (peak sample-and-hold 
device), behavior as you describe is pretty normal for SSB operation; e.g., 
indicated input/output would be MUCH higher on CW or FM than on SSB, because 
the indicators cannot respond in time.

All my amplifiers indicate almost no grid current and not much plate current 
even when run at full power on SSB, but the output is still 1500W PEP as 
measured using correct instrumentation...



-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
Behalf Of KB0NLY
Sent: Friday, March 06, 2009 10:37 AM
To: Steve Katz
Cc: amps at contesting.com
Subject: Re: [Amps] A Symptom of Low Bias?


Homebrew..

Its a FL-2100B that i scavenged to reuse the power supply and
chassis/cabinet as my base for a 6m amp using the GI-7B triode.

http://www.kb0nly.net/6mqro.html  All the info on it...

73,

Scott


----- Original Message ----- 
From: "Steve Katz" <stevek at jmr.com>
To: "KB0NLY" <kb0nly at mchsi.com>; <amps at contesting.com>
Sent: Friday, March 06, 2009 11:10 AM
Subject: RE: [Amps] A Symptom of Low Bias?


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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