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Re: [Amps] Grid Dipping the Pi network in a new amp?

To: "STEVEN & NANCY FRAASCH" <>,"Chuck Curran" <>
Subject: Re: [Amps] Grid Dipping the Pi network in a new amp?
From: "Tom W8JI" <>
Date: Sun, 15 Jul 2007 17:27:14 -0400
List-post: <>
The general condition where a grid dip meter dips the 
deepest is with the highest possible Q, NOT when the tank is 
loaded with a resistance.

If you are not getting a dip and you are using a real grid 
dip meter, it is because you are looking at the tank 
incorrectly or have something wired wrong.

Think of the tank as a transmission line. A normal 
pi-network tank when terminated acts like a line section 
with an electrical length of 130 degrees or so. In fact a 
tank perfectly  tuned on 7MHz for a 3000 ohm tube and 50 ohm 
load resonates when open circuited about 6.9 MHz, so you 
should see a dip near the operating frequency WITHOUT 

Of course this is still largely a useless test, sine it does 
not mean the tank is working as a matching network.

The most useful test is to terminate the tube anode with a 
resistor that looks like the operating load impedance you 
want (use short leads to the resistor). Then you look at the 
output port and look for a low SWR.

I'm going to side with Ian on this one. The largest dip is 
ALWAYS when there is no resistance, and the dip would be 
very close to the working frequency. You will get the 
poorest dip when you follow the advice to terminate the 

You have something else wrong, or have a bad dip meter.

73 Tom

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