Testing EF Johnson 500 tube Ham Radio transmitter following repair High Power AM Plate Modulation

Transmitter arrived D-Lab with no output. Owner suspected loss of High voltage. I gave the transmitter and power supply a thorough inspection. A very nice clean piece, no signs of abuse or modifications. First I verified that the power supply was operating properly. Then I moved into the RF deck. Found many problems all related to loss of grid drive. These transmitters are fairly difficult to work on. Since there is dangerous voltages present, there are interlocks to contend with. Johnson did their best to protect the technician. Yes, I had to bypass safeties while troubleshooting. I used extreme caution, double checked every step I took. These are also extremely heavy transmitters, so a strong bench & carts are highly recommended.

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