A question about possible VHF parasitic oscillations in a VHF
amplifier:
Using a grounded-grid 8877 on 50 MHz, with the tube output capacitance
serving as the only tank capacitance, is there a need for a parasitic
suppressor? The tank circuit would be comprised of only the tube
capacitance and a coil connected directly from anode to B+, with the
usual bypass capacitor, of course. Tuning would be done by
compressing the coil, and output coupling would be a tuned link as was
typical before pi-networks became common.
It would seem that the VHF resonant circuit present at HF using
a pi-network simply is not there and no suppressor would be needed.
If I were to use a separate tuning capacitor, then the unintentional
VHF circuit would appear again, right? Or am I making a fundamental
error here?
73, Bill W7TI
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