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[Amps] MFJ Analyzer for adjusting matching network...

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Subject: [Amps] MFJ Analyzer for adjusting matching network...
From: "KB0NLY" <>
Date: Sat, 21 Feb 2009 01:44:04 -0600
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After all the discussion on the subject of selecting the proper value of the 
plate and loading cap i came across a lot of articles in my research on using 
an MFJ analyzer to do this.  I have access to one so i think i'm going to give 
that a shot.  I found some pretty good explanations how to do this.

""Adjusting the output pi-network: 

ABSOLUTELY REMOVE ALL TUBE VOLTAGES. Leave the tube in circuit. The plate load 
impedance of your amplifier is expressed approximately as: [(plate voltage in 
volts) divided by (1.8 times the plate current in amps)]."" 

For me that would be 2400 plate volts and 600 ma of plate current max, this 
works out to 2222 ohms. So a 2.2k resistor should be close enough.

""Make up a resistance value close to this number with low inductance 
resistors, and temporarily place this resistor string from the tube anode 
connection to ground. This simulates the plate load impedance of the amplifier. 
The purpose of the pi-network in the amplifier is to change this relatively 
high plate load impedance value to 50 ohms for your transmission line. Now, 
hook up a SWR analyzer to the amplifier's RF OUTPUT connector. Adjust the SWR 
analyzer for a frequency of 50.1 MHz Adjust the copper coil windings (slightly 
expand or squeeze together) in conjunction with adjusting the output loading 
capacitor. Adjust for a 1 to 1 SWR reading on the SWR analyzer. When the SWR 
reading is flat, your adjustment is finished. The top RF deck shielding cover 
on this amplifier had a small effect on this setting, so a tiny adjustment was 
necessary when the amplifier was running at full output. It's amazing how close 
this procedure gets your amp to the final settings. If you don't h
 ave a SWR analyzer, consider getting one. Remember to remove the temporary 
resistor you installed during this procedure. ""

Sounds easy enough, or am i missing something here?



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