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Re: [Amps] 6 Meter Pi net and Tuned Input Calculator

Subject: Re: [Amps] 6 Meter Pi net and Tuned Input Calculator
Date: Sun, 15 Jul 2018 11:47:06 -0500
List-post: <>
Don't let the stray caps get ya.

Quoting Jim Thomson <>:

Date: Sun, 8 Jul 2018 20:40:52 -0500
From: "Jim W7RY" <>
To: "AMPS" <>
Subject: [Amps] 6 Meter Pi net and Tuned Input Calculator

<Looking for a pi network calculator that covers 6 meters.

<GM3SEK site just  goes through 10 meters.

<Jim W7RY

## sure it does. I use it almost continually. Just enter what ever freq u want.

##  I use it for  PI nets.    I  also use it for PI  TUNED INPUTS.

##  beware, when using his online calculator, the one thing it wont handle is
say 50 ohms to 50 ohms... like on a tuned input, using a tube with a 50 ohm input Z. No big deal, just enter 50 to 49.... or 49-50 ohms. Similarly you cant enter
75 ohms to 75 ohms... or any other combo  where the Zs  are identical.

## I have used the online calculator for tube amps... from new 475 khz band.....
up to  50.125 mhz ..and everything in between.

## when used for tuned inputs the plate load Z now becomes the 50 ohm xcvr output. The ant
Z  now becomes the desired tube input Z.

## The beauty of his online calculator is.. it factors everything in, like the all important
stray C.....and also the stray L

## On bands like 15-12-10-6m, I typ install a small coil, between plate block cap..and main C1 tune cap. That extra tiny bit of uh, + tubes anode to chassis C, forms a step down L network, making for a reasonable Q to be used. Without it, the typ loaded Q on upper HF is sky high. Then u can also see at a glance how that effect drops off, as you move down in freq, like lower bands.

## I have found on metal tubes like the 3x3, etc, that the anode to chassis C will rise, due to proximity of the lower anode chassis below.... vs testing with LCR meter on the wooden bench. On the wooden bench, I get identical results to Eimac specs. It will also rise due to proximity to side and rear walls etc.

## All this stray C..and intended or un intended uh can easily be measured,and factored in.

## It will also factor in the plate choke XL. Use to small a plate choke on say 160M band, and you will have to use a lot more tune C, since you are in essence, parallel resonating the plate choke anyway.

## same deal with the bifilar used on a GG amp. The 10 uh bifilar on a SB-220 can be used on 160m, BUT the C2 cap on the tuned input will have to be increased by aprx 900 pf.

## The VK1SV spreadsheet is ur generic PI spreadsheet..which wont compensate for all of the above, which is
why we dont use it, or similar  generic PI spreadsheets.

Jim   VE7RF

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