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In Reply to: Old design detail on PPP tubes....... posted by Jimmy on February 2, 2005 at 08:35:54:
They are there to supress parasitic oscillations in the VHF/UHF range. The tubes have plenty of gain there, and the connecting wires have a resonant frequency in that range... so a parallel audio circuit becomes a push-pull UHF oscillator! Sometime a low value resistor is enough, sometimes it's a combination, often a choke wound on a 47 Ohm resistor.
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