[Amps] DC Blocking Capacitor

[Phil Clements]

To avoid affecting the amplifier's tuning and matching characteristics, the
blocking capacitor should have a low impedance at all operating frequencies.
It's reactance at the LOWEST operating frequency should be not more than
about 5% of the plate load resistance. The capacitor must also be capable of
handling, without over-heating or changing value, the substantial current
that flows through it. This current is greatest at the amplifier's highest
operating frequency where tube output capacitance is a significant part of
the total tank capacitance. Therefore, the math can be done to solve for
required C and current ratings to match the planned operating conditions.
The voltage rating of the capacitor should be 25-50% greater than dc voltage
applied to provide a safety margin.

These formulas apply to all blocking capacitors, as they all do the same
thing; block dc, pass RF, and do not affect the circuit in which they are
installed.

(((73)))
Phil Clements, K5PC




-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Bob Easterbrooks
Sent: Tuesday, April 26, 2005 1:27 PM
To: amps at contesting.com
Subject: [Amps] DC Blocking Capacitor

Gentleman, What determines the capacitive value of the DC blocking capacitor

used in a convential shunt fed PI, and can the same rules apply to a simple 
link coupled tank circuit?   I thank you in advance.  Bob, K6JQA 
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