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

[STEVEN & NANCY FRAASCH]

Yes, I am choking over Bob's comments. 

Metal work looks good. 

It looks like your green clip lead is the output, and the red lead is for the 1.8K termination.  Getting this stuff in close and tight is necessary for 10m, but it's probably ok for under 40m. 

I don't see so much of an issue with your layout.  It won't impact getting a resonance on 40m. 

You mentioned tank values that seem a bit different than what I find for a 80m pi-net.  I get for a Qo = 12, the input shunt cap is 250 pf, series L = 8.2 uH, and output shunt cap 1240 pF.  You mentioned you're getting 7 uH for the coil in the 80m postion.  That might be too light.  Look for a resonance higher, around 4 MHz.  Perhaps you can preset components with the L/C meter, re-connect and re-test. 

Steve 



----- Original Message ----- 
From: "Robert Bonner" <rbonner at qro.com> 
To: "Chuck Curran" <ccurran at wi.rr.com>, "STEVEN & NANCY FRAASCH" <sjfraasch at embarqmail.com>, "Tom W8JI" <w8ji at w8ji.com> 
Sent: Tuesday, July 17, 2007 9:29:07 PM (GMT-0600) America/Chicago 
Subject: RE: [Amps] Grid Dipping the Pi network in a new amp? 





Hello Chuck, 

I looked over your photos. 



Here’s what I would have done different.  I can hear Steve choking on his gum. 



The coil would have been in place of where the caps are.  You want to keep the strap to the coil as short as possible and have the UNIT providing all the coil…  However, Inductance is inductance.  My 77DD amplifiers used roller inductors and the ten meter tap was only ¾ of a turn.  It doesn’t take much coil when you are strapping things together. 



The caps are then strapped off the coil.  The lead inductance to them is neutralized with the caps. 



I’d get a flange for the tuning cap and get it grounded.  Definitely strap it to ground solidly.  J 



You can turn the coil on top of the 852 around and have it hook to the back of the cap instead of using a massive strap over to the other side of the coil.  You might want to mount the 852 back somemore from the front to line up the coil better. 



Metal work looks nice. 



BOB DD 





From: Chuck Curran [mailto:ccurran at wi.rr.com] 
Sent: Tuesday, July 17, 2007 8:10 PM 
To: 'STEVEN & NANCY FRAASCH'; 'Robert Bonner'; 'Tom W8JI' 
Subject: Re: [Amps] Grid Dipping the Pi network in a new amp? 



Gentlemen: 



I have attached a group of pictures of the amp construction.  I will make a posting on the amps list server ASAP, I just wanted to provide some visual information too. 



Thanks for all of your comments! 



Chuck WA9POU