- Occasional poster
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- Joined: Mon 11/06/06 2:00 am
- Location: Shropshire, England
In brief, oscillation can result from the combination of stray inductance in the grid circuit, and stray capacitance across the output transformer, plus interelectrode capacitance. In other words, there are stray resonances in both grid and anode, and if they coincide the sh*t hits the fan.
"If trouble is encountered from this residual grid-plate capacity... place a resistance of a few thousand ohms in series with the grid.... such a resistance introduces proportionately more loss at the higher frequencies...and thereby tends to counteract the lower input admittance as the frequency is increased."