[Heathkit] parasitic suppressor

[rbethman]

Jorge,

The C is the interelectrode capacitance *OF* the PA. What you are 
*suppressing* are UNDESIRED harmonics, and PREVENTING or SHUNTING to 
ground unwanted oscillation, i.e., VHF oscillation that develops in PA 
circuits that do NOT have parasitic suppression.

This is also why tube type finals in a radio have neutralizing 
capacitors in the circuit. These are set usually at the highest band of 
the radio, with no *real* drive. You are balancing out the inherent 
circuit tendencies.

Without blockage of parasitic oscillation, the PA very well *CAN* go 
into a self oscillation mode and self destruct.

Bob - N0DGN
>
> A parasitic suppressor, as *most* of us are normally involved with, 
> creates a trap, (an L/C circuit piece), or block if you wish, that 
> simply stops the "undesired" frequencies from passing through the 
> finals, or the linear amplifier.
>
> It can be accomplished by an inductor, (coil), wrapped around a carbon 
> resistor in the plate lead.
>
> Other suppression methods are in the construction phase of an 
> amplification stage, for example:  Grounding the cathode in an amplifier 
> tube such as 572Bs or 813s.  Bypassing 'other' grids such as control 
> grid and screen grids with a high voltage disk ceramic capacitor from 
> pin to ground with ALMOST *NO* lead length.
>
> Bob - N0DGN
>
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> If such a supprssor were an LC parallel circuit, its impedance were maximun
> at the resonance frequency, so this frecuency would not be attenuated by
> the PA because the LC circuit is in series with the anode.
>
> I can not figure how the attenution is accomplished.
>
> Tanks again.
>
> Jorge
> HK6BCC 
>
>
>
>
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