[Amps] Question for All Amp Builders...

[Lee Buller]

You have gotten some very good replies....  I will add my 2 cents.  What the circuit does is to transform the tube output impedance to what your load is....for the most part...50 ohms.  There are some mathematical formulas that give you the answer you need for C and L.  If I remember right, you have to change the reactance  figures to pF and uH.  Then you need to select the right cap....and the right inductor.  The cap is pretty easy, but I've always had issues determining the L part...turns per inch vs. wire size vs diameter, etc.  Well, you will get a ballpark number  Or, use the spreadsheet as indicated.  Or go out and find the web sites where you can plug in the data and it will figure it for you.  I've always had trouble building the right size of coil.  

But, you will need to actually tweak the C and L once you get started.  In the old days, it was a lot of trial and error...and for me...mostly error.  Now it is a little different....  Some guys use a antenna analyzer set on 50 ohms at the output and a resistor on the imput of the tube impedance (from manufacturing specs) and adjust the C and L to get a match.

Do not attempt this with the HV on.  Do it cold!  No HV.

But, the builders you are looking at have done the math and built the circuit...and they did not pull the values out of a hat.  

Your mileage my vary

Lee - K0WA


In our day and age it seems that Common Sense is in short supply.  If you don't have any Common Sense - get some Common Sense and use it.  If you can't find any Common Sense, ask for help from somebody who has some Common Sense.  Is Common Sense divine?

--- On Thu, 2/19/09, KBØNLY <kb0nly at mchsi.com> wrote:
From: KBØNLY <kb0nly at mchsi.com>
Subject: [Amps] Question for All Amp Builders...
To: amps at contesting.com
Date: Thursday, February 19, 2009, 10:13 PM

Got a question for everyone...

When designing an amp how do you determine the value of the tune and load
capacitor?  I have been looking at a lot of designs online for HF and 6M,
i'm currently working on building a 6M myself from a YU1AW design.

Just seems to me there has to be some solid logic behind the values that these
guys put down when they design the schematic for it.

73,

Scott KBØNLY

www.kb0nly.net



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