[Amps] 3CX800A7 Spares - cook them periodically?

John Lyles jtml at losalamos.com
Sat Jul 19 15:41:53 EDT 2014

Damping resistances is a more general term for the more specific types 
like parasitic suppressors (which are slightly tuned to damp only higher 
frequency - VHF - spurious energy). Over the big pond they are sometimes 
called Stoppers. In cavity circuits, we can use  damping resistances 
instead of parasitic suppressors, since the geometry of the resistor 
placement and location alone might determine which frequencies or 'high 
order modes' that the damper helps dampen. Sometimes they are not pure 
resistors but instead are magnetic losses, which do the same thing for a 
high H field area in a circuit. These are materials like ferrite, 
Eccosorb. The whole point here is it de-Q some resonance, either in a 
cavity circuit due to geometry, or in lumped or LC discrete circuit from 
stray inductances and capacitances which set up their own resonances 
around the active devices. In some MOSFET circuits, damping resistances 
are just small series R in the gate leads to help stabilize the device 
from taking off at higher frequencies. In tube circuits, sometimes you 
see a low R like 10 ohms in series with a grid, does the same thing - 
loading the circuit, at some range of frequencies. A tube tester can 
apply DC to the elements to measure its parameters, or just apply beam 
in the tube to help condition and clean it up. In this case, no tuned 
circuits are there, but the tube might try to oscillate itself as  TPTG 
or other topology, just based on the stray inductance and interelectrode 
capacitance. In this case, the solution is to add some R into the 
circuits, damping this.

> Subject: Re: [Amps] 3CX800A7 Spares - cook them periodically?
> I understand the concept (although not the black magic) of parasitic
> surpressors and chokes; but you raise the issue of damping resistances.  What do
> you mean by that?  Where in a triode circuit would they go?
>> Steve  Gilbert
> K1SG
> K1SG at AOL.com

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