I was just thinking about that, whether or not the HV metering should
reference chassis or B-, guess you just confirmed that one for me! I don't
have a HV meter in this amp, but i think the next one i build will have a
meter with a switch to monitor a combo of things.
Definitely taking this experience forward and building another one
eventually for another band. Thinking about 2m SSB now, though i do have
almost 200w there now.
73,
Scott KBONLY
----- Original Message -----
From: "Mike Schelly" <hinrgdj1@comcast.net>
To: <TexasRF@aol.com>; <kb0nly@mchsi.com>
Sent: Friday, March 06, 2009 5:45 PM
Subject: RE: [Amps] A Symptom of Low Bias?
> Good call Gerald,
>
> That little bit of negative grid current used to be a mystery to me also!
> I've always monitored the Hi_V thru a suitible multiplier resistor string
> to
> CHASSIS,
> Wrong!!!! Instead of chassis, the hv meter - should go to B-. I learned my
> lesson.
> Depending on shunts/meter movements it my be more obvious to some than
> others.
>
> TNX, Mike K4EAR
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of TexasRF@aol.com
> Sent: Friday, March 06, 2009 3:23 PM
> To: kb0nly@mchsi.com; amps@contesting.com
> Subject: Re: [Amps] A Symptom of Low Bias?
>
> 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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