Helping a friend with a TL-922.
On 80m, it is suffering from not enough loading capacitance. The peak at low
drive levels is at 1. If driven to 1kw the peak it not attainable, as it
appears to be past the lower limit.
I suspected that maybe the padding capacitor for 80m, or its associated band
switch wiring failed Also the second portion of the load variable cap which is
switched in for 80m. All tested good, including the band switch.
The issue seemed to begin when both tubes were replaced with new RFP 3-500ZG
tubes. At that time the 4.7k resistors and 470uh inductors on the grids were
replaced. The original external wire wound style inductors were NLA, so
standard sealed resistor-like style 470uh inductors were used.
On the upside, the amp now does 1000w with only 50w drive now. So with that
in mind, I wonder if the lower drive requirement is related to the "lack of
sufficient loading" ?
I recall reading in the past that directly grounding the grids requires
increased drive. Thus my suspicion that the new inductors may be the culprit.
Could the lower drive condition be related to the lack of sufficient loading
capacitance?
Eric
K2CB
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