[Amps] QRO HF2000 tank coil Q question

[Jim Thomson]

Date: Mon, 22 Mar 2021 18:37:26 -0500
From: Jim <jimw7ry at gmail.com>
To: amps at contesting.com
Subject: Re: [Amps] QRO HF2000 tank coil Q question

<I recommend an open coil type. Especially on 40 and 80. I tried toroids 
<in my 8877 amp and had the 160 meter unit overheat and start to smoke 
<when on 10 meters!

<Yes, the 160 meter Pi toroid over heated on 10 meters. Even with a 
<shorting band switch. Some sort of weird stray RF.

<Changed the 80-160 tank to a #14 coil wound on a ceramic form. Works great!

<Good luck



<Thanks
<73
<Jim W7RY

##  I gave up on the T225A-2.    With 3 x stacked, they are  2.4 inches od..and  3 inches  tall. 
A piece of airdux aprx the same dimensions   will  provide the same inductance, and  weigh
almost nothing.   I had some airdux in 12 ga,  in two types, and one of em had the turns spaced slightly closer,
which resulted in slightly higher uh, for  a given number of turns.   Runs  stone cold...with a  C1  Q of  8. 

##  per  Owen  Duffy, in  VK land, any tube  operating in class A, AB, or B  already has  7.5  db of  2nd harmonic
attenuation..... before you add the  simple pI net.   He claims  with the pi net..and  a C1  Q  of just 8, the  2nd harmonic
attenuation is  40 db..... which IMO, is more than ample for my needs,   None of my ants are resonant on their  2nd harmonic anyway.
My  F12  40m yagi isnt even resonant on its  3rd  harmonic either.  The 40m yagi does resonate  on 24 mhz. 

##  with experimenting with the roller coil on one amp,  I found that the higher   tank Q  just results in more tank coil heating, and more 
frequent  tuning  when qsying.      Double the  Q, and the  rf current into the coil is  double, which results in  quadruple the power being
dissipated in the coil.

##  an interesting read.  https://owenduffy.net/tx/concept/pi.htm

Jim   VE7RF