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[AMPS] L-Net calculations: Am I doing something wrong?

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Subject: [AMPS] L-Net calculations: Am I doing something wrong?
From: (Jon Ogden)
Date: Thu, 18 Feb 99 09:38:05 -0600
>A good 4x1 will key down 700-800ma. Since key down is your measuring
>point why go for some other value? It will still be darn close to SSB


>I suggest you reread " Care and Feeding" and some of Orrs articles and
>maybe you will not have to ask questions almost daily for a year ( or is
>it 2 years already) plus just to get a basic amp going.

It's been a year.  And from last April until December, I spent maybe 3 days 
rebulding mechanical stuff on the amp.  So....I haven't been working on it 
every day for an entire year.

>>>Why does my power output top out at 800 Watts?  Once I get over 60 
>>watts of 
>>>drive, I get no more power out no matter what I do.  
>>Ä  Sounds like a tuned input problem.  What is C1?
>I asked that question a few weeks ago and got no answer, just more
OK, OK, I'll get you guys that.
>>>In looking at everything I was assuming it was becasue Q was too 
>Altho that Q is very high and can cause problems, where is it written
>that it cannot be used?  At least for a starting point?
>Since I and others have mentioned numerous times that the B&W 850 10M
>coil is almost always modified for a single 4x1 why do you persist in an
>endless barrage of questions?  
>Why not just spend a week doing some real engineering work and report
>that you finally reached the same output efficiency level as probably
>several hundred others have done over the years.

Gee Carl, I think I have been doing some engineering work.  I've done 
calculations for what various Q values are for different Pi-net components.  
The fact that I calculate a Q in the 40s seems to me to be a problem.  OK, so I 
modify the B&W to give me more inductance.  Now, I can't tune the amp because 
my tune C is too large.  So what do I do?  I try the "L-coil" trick that you 
and others have suggested.  I make the coil, I try it out.  And well, it still 
doesn't work correctly.

You say I should report the same output efficiency as others.  Well, the funny 
thing is, I have had no one tell me that they have gotten a 4-1000A to work on 
10M and give 1800 Watts out at 5KV.  Several people have sent me messages 
saying they had all sorts of problems with that beast.  Some say, "Gee, had an 
amp like that once, but I lost all my notes and forgot how I did it."  Some say 
I should lower my plate voltage and not try to run at 5KV on 10M.  There are a 
TON of so-called experts on this reflector.  Seperating the wheat from chaf is 
not an easy task.

I've always learned by asking lots of questions.  Yes, I was that obnoxious kid 
in class who always asked questions.  But it's the way I learn.  I'll admit it, 
I don't know everything about building tube amps.
>On a more positive note, how about scanning in pictures of this beast
>along with a schematic and at least the important component values?  I
>have lost track of what you have any longer, its been that long.  Perhaps
>a picture is worth a few megabytes of more questions and someone may be
>able to spot a problem straight away.

Pictures have been taken.  I have to develop them and scan them.  Schematic?  
Sure.  It's basically a standard amplifier schematic.  But I'll get component 
values, sure.



>>>What light can you shed on this?
>>>Also, how do you determine your peak anode current.  
>>Ä  look at the constant-current characteristic curves.  For good 
>>linearity, pick the highest peak-current curve that has a defined knee 
>>the anode/plate potential equal to the screen-supply voltage.  For the 
>>8166/4-1000A, the highest  such curve is 2.6 peak-amps.  Divide 
>>peak-current by 3 to obtain avg. current.  This is how I arrived at 
>>c. 0.8A figure.  
>Right on the money Rich,  always been my experience in real life 4x1
>>>The current will 
>>>change depending on what amount of drive you have applied to the amp. 
>> So 
>>>I what I think you are saying is that you would need to drive the amp 
>>>that the plate current is at 0.8 A.  But then if you decrease the 
>>>you would change the impedance and hence the match.  Correct?
>>Ä  yes x 3.  The guy who wants to take it easy on his linear amp. and 
>>tunes up with reduced drive, gets a mistune every time.  .
>AMEN !  Along with a 30KHz wide signal when he cranks the drive back up
>without retuning. Come to think of it that must be the popular method on
>the ham bands.

Jon Ogden

"A life lived in fear is a life half lived."

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