Hello all,
have got two YL1050 432 Mhz cavity amps with quarter wave output an folded
back 3/4 wl re-entrant cavity here. Screen grid is grounded and grid 1 is
bypassed by 8 x 470pF leadless disk capacitors.
This amplifier is not stable. At cathode currents above around 600mA the
amplifier tends to turn into a run-away condition. This means that cathode
current,screen current and Power Meter(1,5KW) come up with a full scale
reading, which is obviously not good for the internal tube structure.
Removing drive power restores the normal quiescient current after around
two seconds.
Originally the cavity tuned from 225-400 Mhz (R&S design). After minor
changes it now tunes up to 500 Mhz but here is my question: How can I
neutralize this beast??? Obviously there must be some unwanted feedback
through the tube causing the trouble. I need a very simple way to get rid of
this because access and space within the cavity structure are limited ! Any
ideas are welcome.
Andy DL4XX
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