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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?
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Date: Fri, 19 Feb 1999 21:15:08 -0500

On Thu, 18 Feb 99 09:38:05 -0600 Jon Ogden <> writes:
>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 

There is life beyond the computer !  As many have mentioned, perhaps some
of those formulas are questionable...there are enough of them to even
confuse a bureaucrat.

The fact that I calculate a Q in the 40s seems to me to 
>be a problem. 

An initial problem only.  Has very little to do with getting an efficient
input circuit.

 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? 

Why are there so many other working amps out there with identical setups?

 I try the "L-coil" trick that you and others have suggested. 

I have NEVER suggested the L coil.   Reread my messages.

>make the coil, I try it out.  And well, it still doesn't work 

No suprise there.

>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 

Doesnt suprise me either when people neglect the basics. Add to that the
true condition of the tubes ( 4x1 pulls) most hams use. 

 Some say, "Gee, had an amp like that once, but I lost all my 
>notes and forgot how I did it." my granny has a 53 Corvette in the garage !

Some say I should lower my plate 
>voltage and not try to run at 5KV on 10M. 

No valid reason  to.  But if you dont want to become another wimpout why
not just strip everything and build for 10M only ? Do it 100% right ,
measure everything and THEN add the easy bands?  Give yourself plenty of
LC headroom so that all the new strays wont kill you. Forget Q for the
time being, just experiment for efficiency over a bandwidth that you can
live with without retuning.

 There are a TON of 
>so-called experts on this reflector.  Seperating the wheat from chaf 
>is not an easy task.

There are many more very qualified engineers that read but dont wnat to
get involved because of the non stop nitpicking of  a few.
Working DX beyond the List Nerd level is 90% listening and 10%
transmitting. The same concept holds true in most of life's endeavors.

>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 

Nothing wrong with questions Jon, thats how my kids learned. But with
educated adults there becomes a limit when you narrow into a very, very
specific area.


>>On a more positive note, how about scanning in pictures of this beast
>>along with a schematic and at least the important component values?  
>>have lost track of what you have any longer, its been that long.  
>>a picture is worth a few megabytes of more questions and someone may 
>>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.

Nothing is standard, Ive learned that the hard way.

Sorry for the few day delay in replying but been putting in 13hr days to
cover my trip to NC next week.
It seems like I come home, go to sleep 8hrs, wake up, shit, shower and
shave ( I save on the shave time)  and back to work. That gives me almost
no family time and no hobby time.

73  Carl  KM1H

>>>>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 
>>>the anode/plate potential equal to the screen-supply voltage.  For 
>>>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 
>>> So 
>>>>I what I think you are saying is that you would need to drive the 
>>>>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. 
>>>tunes up with reduced drive, gets a mistune every time.  .
>>AMEN !  Along with a 30KHz wide signal when he cranks the drive back 
>>without retuning. Come to think of it that must be the popular method 
>>the ham bands.
>Jon Ogden
>"A life lived in fear is a life half lived."
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