[Amps] Surge resistor

[TexasRF at aol.com]

Rick, if the big resistor drops  100v at 2A then it must be 50 ohms, right? 
This is a typical value used in  series with the high voltage lead to act as 
low frequency parasitic suppression  circuit.
 
An 8877 has mucho gain at low  frequencies and some really nasty things can 
happen if an audio frequency  oscillation were to take place. The power supply 
filter capacitors and the plate  rf choke and bypass capacitors don't 
necessarily cause the tube plate to "see" a  low enough Z to kill the circuit gain at 
lower frequencies.
 
Installing the 50 ohm resistor can  lower the Q of these nuisance resonance's 
enough to keep things stable and  trouble free.
 
There are probably  some that would say this is balderdash but my personal 
experience with the 8877  on 2m surely supports the story.
 
73,
Gerald  K5GW

 
 
In a message dated 3/21/2007 8:23:33 A.M. Central Daylight Time,  
rstealey at hotmail.com writes:

Tom,  W8JI, says:
>The small glitch resistors in your amp don't do a darned  thing

I am in the process of finishing up my 8877 amp, and the plans  I am using 
show a 0.6 ohm 1 watter and a 50 ohm 50 watter in  series.  So in the event 
of a flashover (milliseconds ?) the 0.5  ohmer is supposed to blow open?  I 
can't see the value of the 50  watter.  In case of extremely high plate 
current, such as hitting  it with full drive and no load, say 2 amps of plate 
current flows and  even then the big resistor only drops 100 volts, and heats 
up 200 watts.  I wouldn't expect a wirewound power resistor to fail 
immediately under  these circumstances, and I can't see how it is protecting  
anything.
What am I missing here?  Is the 50 watter the wrong  type?

I have other topics to discuss relating to control circuitry,  soon.

Rick   K2XT

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