>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?
>
IMO, your analysis is correct, Bill. The difference here is that the
anode resonant frequency is not different from the tank resonant
frequency.
- However, I would be more inclined to put a load C on the output end of
the L and make it a Pi network tank.
Rich---
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|