Date: Mon, 22 Mar 2021 18:37:26 -0500
From: Jim <jimw7ry@gmail.com>
To: amps@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
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