Broadcast & Communications Engineering and Maintenance Services
WKCN-FM 99.3 Harris HT25FM Transmitter 4CX20000A PA Tube Replacement – October 12, 2021
The Eimac 4CX20000A PA tube in the WKCN-FM Harris HT25FM transmitter had gone “soft” after being in service since January 4, 2011. We must admit, a bit over ten years and nine months of service out of a rebuilt tube was really good tube life. Nonetheless, it was time to put a new tube in, since the output of the transmitter was dropping below where we wanted it to be. We had switched the transmitter to manual power control mode, which we had done to keep the transmitter’s built-in logic from trying to pull the screen voltage up to excessive levels. Here’s a detailed rundown on how the tube replacement went, including “before” and “after” photos of the transmitter’s performance, as well as some photos taken during the work.
Photos showing transmitter performance before the tube replacement
So, here we go pulling out the bad 4CX20000A tube and doing a little “cleanup” before installing the replacement tube
Time to put in the replacement Eimac 4CX20000A PA tube
Firing the Harris HT25FM transmitter back up and getting everything tuned after installing the Kennetron replacement Eimac 4CX20000A tube
I will be going back to the site on 10/17/21 to recheck the transmitter’s performance and peak all the tuning again. I will also start the filament management on this new 4CX20000A tube. I’ll try to post that site visit here on the Alabama Broadcast Services, LLC website so visitors can see just how low we’re able to run the filament voltage at that point and produce 100% TPO without excessive screen voltage. The whole point of that is to always run the tube with just enough filament voltage to get 100% power output without so that we don’t burn the tube’s filament up faster than necessary due to excessive heat. When you consider the fact that all of the tube’s power output is essentially produced by heating up a piece of thoriated tungsten to the point that it’s spitting out around 17,500 Watts worth of electrons which the station turns into that beautiful sounding country music which Kissin’ 99 FM (WKCN-FM 99.3) listeners enjoy every day, it’s sort of a miracle of physics and some great engineering that makes all that possible. Some of us will never cease to be amazed at how that works. I’m certainly honored and delighted to be a part of the team which keeps all that happening day-in and day-out. Likewise, I’m delighted that we have the Kissin’ 99 FM transmitter humming along at full power and just doing her thing.