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My First H-P Oscillator, By Robert McGaughey
From SMEC Vintage Electrics Vol. #3, Issue #1 (Now SMECC) |
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Thinking back 50 years ago, this same month, I remember the building of KPRO in Riverside. This Radio Station was an all Collins based installation, which we built from the ground up, and operated at 1440 kHz. The used tower, that had been purchased by the owners, had been operated at a much lower frequency. In addition, the owner Mr. Gleeson, whose son is now a TV news reporter on KABC-TV, wanted to make sure that the tower could be seen from downtown Riverside, so he ordered another 40 foot section to be added to the already too-long radiator. The upshot was, that when we had the field engineer measured the impedance of the antenna, it was slightly less than 8 ohms! The worst part though, was that the transmission pattern was all screwed-up, and at night, we skipped a lot of the outlying areas.
Our deadline to be on-the-air was November 15, 1941, however, two days before start-up we still didn’t have all our ancillary equipment! The sales representative for Presto, with whom we had placed our order for the turntables, made a special trip to Riverside to make sure that we would be ready to go on the air. He brought with him the portable record lathe that we had purchased and two Reko-Kut turntables. These turntables were unmounted, so we installed them into packing crates and mounted our Western Electric playback heads and mercury switches on the turntables. We set the two jury-rigged turntables on two massive pillars of concrete. The control room floor floated around these pillars which pyramided all the way from the ground below. The chief Engineer of the station, Norman Dewes, whom I had worked with when he been the Chief Engineer at KYCA in Prescott Arizona, had experienced turntable movement before. Dewes, prior to his radio engineering work, had been involved with the motion picture studios during the early days of motion picture sound, and remembered the pillars that supported the old ERPI motion picture sound equipment. Another valuable lesson in vibration was provided when Norman and I worked together in Prescott Arizona at KYCA during the 1940's. Harold Stetson, the General Manager-Owner of KYCA, would come storming into the station building, usually stomping in on his heels. Invariably, this would happen while we would be playing a transcription, and sometimes the vibration would cause the head to skip all the way across the disk!
With the deadline for having KPRO on-line approaching, the helpful sales representative stayed very late with us until we had everything operating properly. He had also brought with him an audio oscillator which was the sole product at that time of a couple of Stanford Engineering School graduates who had formed a company using their hyphenated names, Hewlett-Packard. By the way, the representative's name was Norman Neely! This little audio oscillator was called the 200-A and was based on a novel R/C design.
I remember two instances of the 200-A oscillator standing us in good stead. Our station was located in close proximity to a residential area and the neighbors complained to the FCC that we were interfering with their reception of other stations. James Chappel, the radio inspector for the FCC at the time, made a surprise visit to our station implying that we were overmodulating. We were able to verify the readings of our modulation meter by feeding a tone from the 200-A through the transmitter and then to an audio bridge. This signal, along with the RF sample was then applied to the horizontal and vertical channels of an old Dumont scope. I remember the drill well, and proved during an on-the-air program for the inspector, that or signal was correct. The problem lay in the AC/DC receivers that were used close to our station. There was enough RF pickup through the power line in these receivers to cause problems. This was due to the combination detector-amplifier tube's high gain and the high meg resistance used to self-bias it, which would cause it to act as a grid leak detector. I also remember using the oscillator at remote sites to improve the quality of the phone line transmission. I would send a tone to the control room from the remote site, and the engineer there would try to equalize the telephone line for better frequency response.
In 1960, when I was in charge of an engineering project for the military at Hoffman, I specified a lot of HP equipment. Only once did I make an error by purchasing 8 Hewlett-Packard oscilloscopes. These oscilloscopes, I believe, were Hewlett-Packard's first attempt, and they really weren't very good. Due to this experience, I remember that on the next project I specified that we buy Tektronix, which I believe Neely had stopped representing by then. -RM |
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