After five or ten minutes the output on my T4XB will fall slowly from 100W to 30W. The plate current till fall from 300 ma to 200 ma. The bias remains 60 ma. All voltages on the finals and the driver are according to specs. Resistors R23, R24, R26, R30, R31, R32, R33 and R36 show no sign of fatigue and are according to specs. The only exception is the voltage on the control grids of the 6JB6s. It is -52 V instead of - 62V.
When the output falls to 30W, a new tuning will briefly increase the output to 50W. If the GAIN is turned from 12 to 2 o'clock, the output will rise to 80 W, but soon fall again to 30W or less. In some cases it will disappear completely, until the transmitter has cooled down. The same thing happens when the transmitter works in standby only, and when it uses the vfo of my R4B. I have replaced all tubes, wriggled the tubes in their sockets, tightened all accessible screws and cleaned the band switch. I have checked the X-tals in the Q3 transistor oscillator and in the carrier oscillator when the output is dying. They can still be heard on my monitor receiver. So what to look for, gentlemen? 73 Peter OZ8CTH
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