Thanks for the answer, Larry.
73
Morel
4X1AD
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Larry Benko
Sent: Monday, May 18, 2015 6:16 AM
To: amps@contesting.com
Subject: Re: [Amps] Question about 4CX800 amplifiers
Morel,
I would not call a series LC circuit a "rejection" in this case. 20pF in
series with 150nH has a resonant frequency of 91.9MHz. In this application
I am nearly certain they are for impedance matching.
20pF in series with 150nH acts like:
20pF at low frequencies
20.5pF @ 14MHz
22.1pF @ 28MHz
30.5pF @ 54MHz
The wiring of the input circuit, the capacitance of the grid to ground, the
50 ohm 100W resistor etc. probably did not match well enough with just fixed
capacitors. It is a very common impedance matching technique to use LC
circuits above or below the resonant frequency to act as frequency variable
capacitors or inductors.
73,
Larry, W0QE
On 5/17/2015 4:01 AM, Morel Grunberg wrote:
> Hello guys,
>
> I wonder if someone can explain the presence of two LC rejections (20pF
> series with 150nH) in the input board of ACOM amplifiers with 4CX800 /
> GU-74B tubes (ACOM 1000, 2000).
>
> Thanks in advance,
>
> 73
>
> Morel 4X1AD
>
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