If there is a plate voltage metering circuit, there could be a sneak path
for this current to flow through the grid meter. If it does, it would be in the
reverse direction compared to normal grid current.
Assuming your bias circuit is located between cathode and ground, the B-
should be connected to cathode. The plate voltmeter (if there is one) return
should also be connected to the cathode.
73,
Gerald K5GW
In a message dated 3/6/2009 2:05:23 P.M. Central Standard Time,
kb0nly@mchsi.com writes:
I can borrow a scope and check that, I found a website explaining basically
the same way you just described! I have always just used a good peak
reading meter but I don't have much for options on 6m yet, I want to build
or buy something eventually. I have a Heathkit HM-2102 that i used for 2M,
but it can be used for 6M by changing one cap value and recalibrating it so
i will do that along with the modifications to increase its full scale range
that seems to be pretty popular and known to work on them.
Can you suggest however why the grid meter would read a negative value on
keyup with no drive??
As for overdriving it, i'm keeping the drive to 20W as the spec sheets for
this tube shows 10-20W max. I also plan on building an ALC circuit for the
radio to keep it at 20W or less when on 6M. The FT-847 has a lot of info
online regarding this, its not really interfaced to the amp, its a circuit
connected to the ALC jack of the radio and then adjusted to keep the exciter
at a specific level regardless of the front panel control.
73,
Scott
----- Original Message -----
From: "Gary Schafer" <garyschafer@comcast.net>
To: "'KB0NLY'" <kb0nly@mchsi.com>; <amps@contesting.com>
Sent: Friday, March 06, 2009 1:52 PM
Subject: RE: [Amps] A Symptom of Low Bias?
> 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
>>
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
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