[Amps] 6 Meter Pi net and Tuned Input Calculator

[Jim Thomson]

Date: Sun, 8 Jul 2018 20:40:52 -0500
From: "Jim W7RY" <jimw7ry at gmail.com>
To: "AMPS" <amps at contesting.com>
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.


<Thanks
<73
<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 fins..to 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