[MRCA] VRC-12
Ray Fantini
RAFANTINI at salisbury.edu
Fri Dec 9 14:03:12 EST 2016
Have an issue with the VRC-12 dropping output power from 35 watts to maybe 5 watts then down to almost nothing after it has been transmitting for more than three or four minutes. All the HV supplies are good and the voltages don't drop. The grid drive to V6101 is good at around 100 mW and stays constant regardless of output or lack thereof and when the power drops off see a decrease in the load on the 28 volt supply feeding the radio as suspected because the amplifier is not working as hard as it was. Checked the one tube on my TV-10 and it was ok but the PA tube don't look tube checker friendly, also intend to disassemble the whole mess this weekend and clean the contacts on the band switch along with also checking power prior to the output filter but also wanted to ask here in case anyone had expense with this radio and what PA tube failure looks like or other issues in the PA. If allowed to cool down can go back and get full power for three or four minutes but after it starts to fail won't get full power until after the radio has been off for a while.
Attached is a JPEG of the amplifier, all comments welcome!
Ray F/KA3EKH
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