Post by dbsteff on Sept 28, 2008 13:39:54 GMT -5
WLRS ’68 and the Lightning Strike
I recounted this experience to WLRS in a few paragraphs, which they were kind enough to post on their webpage. Since I didn’t go into much detail on the matter, I thought it might be interesting to do so here. I have placed it in its own thread, as I didn’t want to bore to death the non-technical readers.
I was in class at UEI in Shively, on this particular occasion, when one of the secretaries from the front office knocked on the classroom door, and entered to speak in a whisper to the instructor. He nodded, at which point the secretary motioned for me to follow her into the corridor.
She informed me that WLRS had called and said they had been knocked off the air in the violent thunderstorm, still raging outside, and that they were unable to get the transmitter back up. They wanted me to come immediately. She said I was excused to go.
I went back into the classroom long enough to gather up my books, etc. and head for the parking lot. I got drenched just traversing the parking lot to my car. Soon I was driving up the “Dixie-Die way” (do they still call it that?) toward downtown Louisville.
When I arrived at the station, I went, first, to the control room, where the remote control panel for the transmitter was located. (You can see that control panel in some of the pics posted here on the WLRS page) It was a black panel that Clarence had hand made. It had the necessary three meters to satisfy the transmitter log, and control buttons to start the transmitter filaments and, when the warm up period had timed-out, to apply the plate voltage to the final amplifier.
Sure enough, all the pilot lamps were out and the meters lying on their respective 0 pegs. There was no response from operating any of the remote control pushbuttons. The DJ who greeted me when I arrived seemed correct in his diagnosis, based on the flash of lightning and clap of thunder that had taken us off the air, we had, as he had suggested, taken a direct hit on the stick.
My initial thought was that we had suffered a big enough power surge to kick out the main breaker in the transmitter shack, and I would simply need to go up on the roof and reset it. I retrieved the keys required to get into the transmitter shack and into the equipment room on the roof. I made my way to the elevator and up to the roof, actually the floor below, from where one had to climb a final set of stairs and enter the equipment room with a key. Anyway, I made my way to the transmitter shack and unlocked the door.
As soon as I stepped inside the transmitter shack, that unhappy smell, known to all technicians and engineers, hit my nose. You know, the mephitic smell of burned resistors or other electronic parts. I knew, immediately, this wasn’t going to be as simple as resetting a circuit breaker.
Indeed, the main breaker on the transmitter was kicked-out. I reset it. It remained, to my great relief, in the on position. Then, I tried to engage the filaments. This action, not only applies power to the filaments of the vacuum tube in the final amplifier, but also powers up the exciter and other support equipment inside the transmitter, including the power supply. As soon as I flipped the momentary key-style switch to power up the filaments, the main breaker kicked out again. I knew I was in big trouble.
I switched off the main breaker and went to the back of the Transmitter and opened the doors. I was looking for anything obvious. The smell became all the more intense and could be traced to the power supply section.
Part of the marketing hype for the RCA BTF 10D transmitter, which is what this one was, was that it had a “Solid State” power supply. While true on it’s face, the way this was accomplished with 60s technology was to place a phenolic board from the top to the bottom of the cabinet which was populated with a string of “top hat” diodes with balancing resistors across each diode to balance the PIV equally across the string of diodes. Hardly an elegant solution, but still, “solid state” as advertised.
I wonder if that transmitter is still in use?... Or how many BTF 10D’s are still in use, have any of you any experience with one?
Anyway, the smell told me that this diode string was damaged, to what extent was difficult to tell. I disconnected it long enough to power up the transmitter and see what else was blown up. I defeated all the interlocks, which normally power down the transmitter if the doors are opened and short out the lethal voltages that might be stored in capacitors such that they don’t pose a serious risk to the technician. Having done so, I could then power up the transmitter with the doors still open. Any of you who work on transmitters of that era are familiar with this procedure.
Once I did so, I discovered that the exciter wasn’t working either. It was not dependant upon the particular power supply I had disconnected, so I knew I was facing multiple problems.
Clarence was out of town, so the station manager had called, not only me, but an engineer that was a friend of Clarence and who worked at WHAS. He arrived in the transmitter shack about this time. I can’t remember his name. I showed him what I had discovered to that point. He shook his head and only said: “Good Luck” then left.
Clarence had been called about our trouble and phoned in on the line in the transmitter shack. I told him we were in big trouble. He said he’d hop the next flight and be back as quickly as he could, and gave me some instructions on what to do until he arrived.
I was relieved. I hadn’t had that much experience with this transmitter, and so it wasn’t intuitive as to how to proceed. I was never so happy to see a face as I was to Clarence’s, when he arrived.
He made his own examination, looked at me and shook his head slowly.
To make a long story at least a little shorter, we spent three days off the air, working frantically to repair the transmitter. This involved Clarence on the phone with RCA, and RCA, in turn, air shipping us replacement parts. In this case, air shipping meant buying a seat on a commercial airliner and in some cases, depending on the fragility of the part, strapping the thing into that seat. Then, one would pick the part up at the ticket counter when the flight arrived, or go onto the flight to retrieve it directly. Those were, of course, pre-terrorism days, and none of the TSA type restrictions were in place, so it was no problem.
Once the power supply was corrected, we were proceeding to see what condition the final amplifier was in. Again, each time we would try to apply plate voltage to the final, a 4CX4000A, if memory serves, the breaker would kick out. Seemed like every section of this poor transmitter had been wiped out.
Clarence had gone downstairs to take a break. We had been working for hours without any sleep and we were both exhausted. I agreed to remove the plate lead wire, in the meantime to see if even the final amp was shorted. Anyone familiar with that tube knows it wouldn’t be easy to short it out…..it’s huge and rugged….still excess plate current was the problem we now faced.
We had powered down the transmitter before Clarence left to go downstairs and stretch out for a nap on the sofa in the executive suite. I used the shorting rod, which you techs know all about, to go around the transmitter and short out all the caps to bleed off any residual charge. Well, I missed one and it found me. It was a ceramic “doorknob” style high voltage cap. It was the screen bypass cap, it was still holding a 20KV charge. I was being a good little tech, I had one hand in my pocket, as is the ritual, but….I was leaning on the cabinet frame at my elbow and using a ratchet and socket to loosen the connection eyelet from the final, At some point the ratchet handle, which extended well beyond my fist holding it, swung up and contacted this screen bypass cap.
I became the “R” in an unhappy R-C network. The current that ran from my fist to my elbow delivered a shock sufficient to throw me back against the wall behind the transmitter. I don’t know if striking my head did it, or the shock, itself, but I sensed myself blacking out. I assumed I had just been killed, as I had absolutely no control over the fact that I was losing consciousness. I remember thinking to myself….”well I always wondered what this would be like” I slid down the wall onto my butt as I passed out.
I came to a few minutes later, sitting on the floor, with this awful copper taste in my mouth, but was relieved to still be alive. I wanted to get to my feet and go downstairs, but discovered that I had little control over my muscles. I sat there for a while until I slowly regained that control. I’ve always been thankful that it only got me from my hand to my elbow. Had it gotten me from hand to hand…..well, you might well not be reading this.
Ultimately, the reason for the high plate current proved to be outside the transmitter. We bled off the dry nitrogen from the heliax connecting the transmitter to the antenna, and placed the transmitter on its dummy load. Then, everything worked fine. It appeared that we had a shorted antenna. We got out the “megger”, which many of you are probably familiar with, and determined that, indeed, we had a short. Clarence looked me and, again, slowly shook his head.
Clarence scaled our mast and examined our antenna bay. He found no obvious sign of shorts. When he returned, we sat there across from each other, on the floor of the shack, each pondering what to do next.
Suddenly, Clarence got up went over to the heliax at the point where it entered the shack any began shaking it wildly, even hanging from it with his whole weight as he did.
I thought….”Poor guy, the stress has been too much and he’s lost it.”
His frenetic shaking was almost frightening.
Then I could hear a sort of “PLINK” sound from inside the heliax, followed by the sound of something clearly rattling its way down the length of the heliax to fall out the end and onto the floor. It looked like a pencil lead from a mechanical pencil.
Clarence looked me and smiled widely. “Hand me the megger” He said.
Sure enough, our short was now eliminated. The lightning had carbonized this little dendrite from the center conductor of the heliax to its shield. I had never seen anything like it. I don’t know if I’d have ever found it. I might have determined that it was the heliax, not the antenna, eventually, but I’d have spent all that wasted time replacing the heliax, needlessly.
At last, after repressurizing the heliax, and doing some other clean up chores, we were back on the air.
Clarence and I were all the closer after this incident. We had done battle together, and we had won.
I recounted this experience to WLRS in a few paragraphs, which they were kind enough to post on their webpage. Since I didn’t go into much detail on the matter, I thought it might be interesting to do so here. I have placed it in its own thread, as I didn’t want to bore to death the non-technical readers.
I was in class at UEI in Shively, on this particular occasion, when one of the secretaries from the front office knocked on the classroom door, and entered to speak in a whisper to the instructor. He nodded, at which point the secretary motioned for me to follow her into the corridor.
She informed me that WLRS had called and said they had been knocked off the air in the violent thunderstorm, still raging outside, and that they were unable to get the transmitter back up. They wanted me to come immediately. She said I was excused to go.
I went back into the classroom long enough to gather up my books, etc. and head for the parking lot. I got drenched just traversing the parking lot to my car. Soon I was driving up the “Dixie-Die way” (do they still call it that?) toward downtown Louisville.
When I arrived at the station, I went, first, to the control room, where the remote control panel for the transmitter was located. (You can see that control panel in some of the pics posted here on the WLRS page) It was a black panel that Clarence had hand made. It had the necessary three meters to satisfy the transmitter log, and control buttons to start the transmitter filaments and, when the warm up period had timed-out, to apply the plate voltage to the final amplifier.
Sure enough, all the pilot lamps were out and the meters lying on their respective 0 pegs. There was no response from operating any of the remote control pushbuttons. The DJ who greeted me when I arrived seemed correct in his diagnosis, based on the flash of lightning and clap of thunder that had taken us off the air, we had, as he had suggested, taken a direct hit on the stick.
My initial thought was that we had suffered a big enough power surge to kick out the main breaker in the transmitter shack, and I would simply need to go up on the roof and reset it. I retrieved the keys required to get into the transmitter shack and into the equipment room on the roof. I made my way to the elevator and up to the roof, actually the floor below, from where one had to climb a final set of stairs and enter the equipment room with a key. Anyway, I made my way to the transmitter shack and unlocked the door.
As soon as I stepped inside the transmitter shack, that unhappy smell, known to all technicians and engineers, hit my nose. You know, the mephitic smell of burned resistors or other electronic parts. I knew, immediately, this wasn’t going to be as simple as resetting a circuit breaker.
Indeed, the main breaker on the transmitter was kicked-out. I reset it. It remained, to my great relief, in the on position. Then, I tried to engage the filaments. This action, not only applies power to the filaments of the vacuum tube in the final amplifier, but also powers up the exciter and other support equipment inside the transmitter, including the power supply. As soon as I flipped the momentary key-style switch to power up the filaments, the main breaker kicked out again. I knew I was in big trouble.
I switched off the main breaker and went to the back of the Transmitter and opened the doors. I was looking for anything obvious. The smell became all the more intense and could be traced to the power supply section.
Part of the marketing hype for the RCA BTF 10D transmitter, which is what this one was, was that it had a “Solid State” power supply. While true on it’s face, the way this was accomplished with 60s technology was to place a phenolic board from the top to the bottom of the cabinet which was populated with a string of “top hat” diodes with balancing resistors across each diode to balance the PIV equally across the string of diodes. Hardly an elegant solution, but still, “solid state” as advertised.
I wonder if that transmitter is still in use?... Or how many BTF 10D’s are still in use, have any of you any experience with one?
Anyway, the smell told me that this diode string was damaged, to what extent was difficult to tell. I disconnected it long enough to power up the transmitter and see what else was blown up. I defeated all the interlocks, which normally power down the transmitter if the doors are opened and short out the lethal voltages that might be stored in capacitors such that they don’t pose a serious risk to the technician. Having done so, I could then power up the transmitter with the doors still open. Any of you who work on transmitters of that era are familiar with this procedure.
Once I did so, I discovered that the exciter wasn’t working either. It was not dependant upon the particular power supply I had disconnected, so I knew I was facing multiple problems.
Clarence was out of town, so the station manager had called, not only me, but an engineer that was a friend of Clarence and who worked at WHAS. He arrived in the transmitter shack about this time. I can’t remember his name. I showed him what I had discovered to that point. He shook his head and only said: “Good Luck” then left.
Clarence had been called about our trouble and phoned in on the line in the transmitter shack. I told him we were in big trouble. He said he’d hop the next flight and be back as quickly as he could, and gave me some instructions on what to do until he arrived.
I was relieved. I hadn’t had that much experience with this transmitter, and so it wasn’t intuitive as to how to proceed. I was never so happy to see a face as I was to Clarence’s, when he arrived.
He made his own examination, looked at me and shook his head slowly.
To make a long story at least a little shorter, we spent three days off the air, working frantically to repair the transmitter. This involved Clarence on the phone with RCA, and RCA, in turn, air shipping us replacement parts. In this case, air shipping meant buying a seat on a commercial airliner and in some cases, depending on the fragility of the part, strapping the thing into that seat. Then, one would pick the part up at the ticket counter when the flight arrived, or go onto the flight to retrieve it directly. Those were, of course, pre-terrorism days, and none of the TSA type restrictions were in place, so it was no problem.
Once the power supply was corrected, we were proceeding to see what condition the final amplifier was in. Again, each time we would try to apply plate voltage to the final, a 4CX4000A, if memory serves, the breaker would kick out. Seemed like every section of this poor transmitter had been wiped out.
Clarence had gone downstairs to take a break. We had been working for hours without any sleep and we were both exhausted. I agreed to remove the plate lead wire, in the meantime to see if even the final amp was shorted. Anyone familiar with that tube knows it wouldn’t be easy to short it out…..it’s huge and rugged….still excess plate current was the problem we now faced.
We had powered down the transmitter before Clarence left to go downstairs and stretch out for a nap on the sofa in the executive suite. I used the shorting rod, which you techs know all about, to go around the transmitter and short out all the caps to bleed off any residual charge. Well, I missed one and it found me. It was a ceramic “doorknob” style high voltage cap. It was the screen bypass cap, it was still holding a 20KV charge. I was being a good little tech, I had one hand in my pocket, as is the ritual, but….I was leaning on the cabinet frame at my elbow and using a ratchet and socket to loosen the connection eyelet from the final, At some point the ratchet handle, which extended well beyond my fist holding it, swung up and contacted this screen bypass cap.
I became the “R” in an unhappy R-C network. The current that ran from my fist to my elbow delivered a shock sufficient to throw me back against the wall behind the transmitter. I don’t know if striking my head did it, or the shock, itself, but I sensed myself blacking out. I assumed I had just been killed, as I had absolutely no control over the fact that I was losing consciousness. I remember thinking to myself….”well I always wondered what this would be like” I slid down the wall onto my butt as I passed out.
I came to a few minutes later, sitting on the floor, with this awful copper taste in my mouth, but was relieved to still be alive. I wanted to get to my feet and go downstairs, but discovered that I had little control over my muscles. I sat there for a while until I slowly regained that control. I’ve always been thankful that it only got me from my hand to my elbow. Had it gotten me from hand to hand…..well, you might well not be reading this.
Ultimately, the reason for the high plate current proved to be outside the transmitter. We bled off the dry nitrogen from the heliax connecting the transmitter to the antenna, and placed the transmitter on its dummy load. Then, everything worked fine. It appeared that we had a shorted antenna. We got out the “megger”, which many of you are probably familiar with, and determined that, indeed, we had a short. Clarence looked me and, again, slowly shook his head.
Clarence scaled our mast and examined our antenna bay. He found no obvious sign of shorts. When he returned, we sat there across from each other, on the floor of the shack, each pondering what to do next.
Suddenly, Clarence got up went over to the heliax at the point where it entered the shack any began shaking it wildly, even hanging from it with his whole weight as he did.
I thought….”Poor guy, the stress has been too much and he’s lost it.”
His frenetic shaking was almost frightening.
Then I could hear a sort of “PLINK” sound from inside the heliax, followed by the sound of something clearly rattling its way down the length of the heliax to fall out the end and onto the floor. It looked like a pencil lead from a mechanical pencil.
Clarence looked me and smiled widely. “Hand me the megger” He said.
Sure enough, our short was now eliminated. The lightning had carbonized this little dendrite from the center conductor of the heliax to its shield. I had never seen anything like it. I don’t know if I’d have ever found it. I might have determined that it was the heliax, not the antenna, eventually, but I’d have spent all that wasted time replacing the heliax, needlessly.
At last, after repressurizing the heliax, and doing some other clean up chores, we were back on the air.
Clarence and I were all the closer after this incident. We had done battle together, and we had won.