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[AMPS] Input Tuned Circuits with Powdered Iron Toroids

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Subject: [AMPS] Input Tuned Circuits with Powdered Iron Toroids
From: (Jon Ogden)
Date: Mon, 8 Feb 1999 22:53:03 -0600
>A class B amplifier produces many harmonics as it switches from
>conducting to non-conducting, and the input tuned circuit must provide
>an excellent input termination impendance not only at the fundamental
>frequency, but also at the 3rd harmonic and ideally at the 5th harmonic
>as well.   This would not be a problem if it were a Class A amplifier,
>but that's certainly not practical for a high power RF amplifier!

OK.  That makes sense.
>Even a  short piece of RG-58 between the input tuned circuit and the
>tube socket significantly increases the input termination impedance at
>the harmonic frequencies.  I discovered this 25 years ago when I
>originally built these amps, I had only about 12 inches of RG-58 between
>the tuned circuit and the socket.  The 10M amp produced less than 1000
>watts output with 100 watts drive and the tube ran brilliant red!  The
>15M amp produced only 1200 watts and the 20M amp had only1300-1400 watts
>output with 100 watts drive.  Moving the tuned circuits to the tube
>sockets made all of the amps perform essentially identical with 1500
>watts output with 80 watts drive.

Hmmm....Could this be another reason why my gain is flat topping on the 
upper bands?  On 10M, my power out is barely 800 watts with anything over 
80 watts in.  Of course my tank circuit is yet another 
question............Perhaps it's multiple things.

I have about 6 inches or so of RG-58. 

Now, with a single band amp, I can say that it would be pretty simple to 
put your matching network right at the tube socket.  But what about a 
multiband amp such as I have?  It will get real, real messy putting the 
caps and coils for 5 bands at the socket of the amp along with filament 
chokes, etc.  What's a good compromise distance?

>By the way, my mother's maiden name is Ogden!

Well, then there is a fair chance we are related!  I believe all the 
Ogden's can trace back to a common ancestor who moved here from Wales.  
And I am quite sure I do have some family out in your neck o' the woods.



Jon Ogden
KE9NA    <--- CHECK IT OUT!  It's been updated!!!!!

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

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