The “Brennan” – The Power Behind WAPE

It can be said with great certainty that WAPE had a sound which was unique.  Some said the station “jumped off the dial”; loud without being distorted with a dynamic, full sound which was impossible to duplicate, some say until the introduction of fully solid state transmitters in the 1990’s.  The WAPE “sound” can for the most part be attributed to its most unique component, the custom designed and built transmitter.

When engineers speak of “The Brennan” the do so using the same terms of endearment that a man would use when he reminisced about the car he once owned which is now a classic, or that favorite girlfriend who got away.  All agree that it was a sight to behold in its operation and found its grand size a benefit when it came to service.

The WAPE transmitter at Orange Park was the fourth in a series designed and built by the Brennan/Benns team. There would be a total of seven once the 10,000 watt model was built for the stations night site in Baldwin.

The Transmitter Family Tree

Transmitter number one was the 10,000 watt model installed at WVOK in Birmingham.  While all designs and construction were cooperative efforts between Billy Benns, Bill and Cyril Brennan, a greater part of the design credit for this 1947 model goes to Billy Benns.  Building this first transmitter would involve all three brothers, with work going on in two states.  In the days before WVOK signed on the air, Cyril and George Blaskow were ending their terms of Army service at Ft. Monmouth, New Jersey.  In these waning days, they would put parts together for the transmitter and ship them back to Birmingham.  A lot of the legwork for this project would be handled by Dan, who was fresh out of high school.  Responsibility for the final construction and assembly would go Bill and Billy.  Operating voltages for the transmitter were generated by a massive military surplus radar power supply.  This insured that there was ample power to accommodate the Class C plate modulated output stage. 

The original 10,000 watt WVOK transmitter.

There were three early performance issues that had to be overcome.  The first was a very narrow frequency response; even though the unit passed inspection, its lack of fidelity was initially noted by the FCC.  A second issue was a detectable hum in the audio. This was later remedied with the replacement of tubes in the final stage which used a different filament material (thoriated-tungsten).  Finally there was an issue of distortion – more than likely made worse by the hum from the AC power supply to the tube filaments, which as noted in an early part of this history, was quickly corrected and successfully fought by Billy Benns with the FCC. 

The next two projects would represent great leaps in both the design and magnitude of the transmitters.  WVOK’s grant in 1949 to increase its power from 10,000 watts to 50,000 watts would open the door for the Brennan/Benns team to incorporate unique knowledge acquired by Bill during his time with National Union Tube Company.  Bills assignments at National took him to the commercial side of the business where transmitting and industrial tubes were manufactured.  It was while doing this work that he put his knowledge to the test by extrapolating, or extending out, the electrical performance curves of high power radio tubes.  He found that the tube designs could comfortably accommodate an additional 50% or greater operating load during peak conditions.  Bill gave Cyril and George Blaskow the specifications for the exact tubes to use in the final amplifier stage of the transmitter.  These were incorporated into the 50,000 watt design for WVOK which would use the newer Doherty High-efficiency Amplifier. 

The Doherty amplification circuit is named after its creator, William H. Doherty who revealed the amplification method in a paper which was presented at the May 1936 annual convention of the Institute of Radio Engineers in Cleveland, Ohio, and published by Bell Labs soon thereafter.  Western Electric was one of the first manufactures to incorporate this new design, but only in its high powered transmitters.  This new circuit differed from the more popular Class B amplifiers used in most transmitters and the Class C used in the original 10,000 watt WVOK design in that it utilized two tubes for signal amplification, instead of a single one.  Most Class B transmitting circuits were 30 to 35 percent efficient.  By comparison, the Doherty Amplifier delivered efficiencies of 60 to 65 percent.

WVOK's 50,000 watt transmitter

Once the WVOK transmitter came on the air, the pure-tungsten filaments used in the final and driver stages created such a hum that a special feedback circuit had to be designed and installed to reduce this condition.  A few years later the original tubes with new ones, which used thoriated-tungsten filaments.  This modification, first used in the new design of the WBAM transmitter, reduced the hum to the extent that the feedback circuit could be removed.  Hum was further reduced by the lower filament heating current required by the new tubes. 

The third Brennan/Benns transmitter would affirm, what was up until that time, the greatest power increase ever granted to an AM station by the FCC.  Applicants for new stations would often understate their technical facilities in order not to attract the attention of other broadcasters, who may try in one way or another to block or delay the new station.  The original construction permit for WBAM was for an operating power of 250 watts daytime.  By 1951, the FCC would grant a modification to the stations construction permit with an increase in power to 50,000 watts.  WBAM expected to spend $53,500 on a directional antenna and a second hand transmitter.  Three years would be spent in an FCC proceeding which examined the issue of daytime sky wave interference caused by the new WBAM construction permit and another permit which was issued to cover a radio station in Orlando, Florida on the same frequency.  What emerged in 1954 was the completed third Brennan/Benns transmitter; another 50,000 watt model based on the Doherty design, nearly identical to that at WVOK. 

The third "Brennan" - WBAM

Fully expecting to deal with the same hum issue from the filament voltage which was in the original design of the WVOK transmitter, a hum-bucking feedback circuit was also included in the WBAM transmitter.  It was while building the transmitter that Cyril and George Blaskow, who was by this time Chief Engineer at WVOK, decided to try different tubes in the final stage of the transmitter; tubes with thoriated-tungsten filaments.  It was the discovery of the great performance characteristics of these tubes in the WBAM transmitter that lead to the two above-mentioned modifications in the transmitters at WVOK.

The period of 1957 to 1959 would be a busy one for transmitter design and building for the Brennan/Benns team.  While there is much overlapping of dates, it is known that the following transmitters were designed and built by the team within this three year period; number four in 1958 – the WAPE 25,000 watt main transmitter in Orange Park, number five in 1958 – a 1,000 watt main transmitter for WEUP in Huntsville, Alabama and number six in 1959 – a 1,000 watt back-up transmitter for use at WFLI in Lookout Mountain, Tennessee.  (As noted earlier, the seventh and final Brennan/Benns AM transmitter was the 10,000 watt model used at the WAPE night site.)

The WAPE “Brennan”

The shimmering gold panels stretched for nearly 25 feet along then entire wall of the engineering room.  So great was its appetite that it was fed by direct 4,160 volt electrical service provided by the Clay County Electrical Co-operative.  Cooled by a series of water pipes which circulated to a fountain in front of the building, the WAPE transmitter at Orange Park would benefit from the knowledge gained from all of the Brennan/Benns designs which preceded it in operation.

Once again, the highly efficient Doherty circuit would be at the heart of the transmitter with one new modification.  By the late 1950’s, Continental Electronics had purchased the radio transmitter division of Western Electric.  This gave Continental the rights to produce transmitters using the Doherty amplifier.  It’s initial Doherty production line consisted of the 315 and 316 models, which were limited to 10,000 watts.  By 1957 a 50,000 watt model was introduced at the Continental 317.  There were three of these transmitters put into service at KRLA – Pasadena (Los Angeles), CA, CKWX – Vancouver, Canada and WDIA in Memphis, Tennessee.  Ironically, WDIA also shared an FCC milestone of sorts with WBAM, having been granted a power increase from 250 watts to 50,000 watts in 1951 – the same year as the Brennan station in Montgomery.  WDIA also began broadcasting with 50,000 watts the same year as WBAM – 1954 – with a Western Electric transmitter, the predecessor to the 317.

WDIA’s transmitter would provide some electrical inspiration for the WAPE project.  Cyril had heard about some of the new designs incorporated into the new Continentals, and one was with driving distance of his home base in Montgomery.  This latest Doherty design incorporated a circuit modification known as a grounded-grid amplifier.  There were several advantages to the grounded-grid; most prominent were its operational stability and the elimination of the need for a separate power supply for the grid bias voltages of the tubes (tetrodes).

Photo of one of the final tubes and water cooling pipes of the WDIA Continental 317 taken by Cyril Brennan.

Once the design parameters had been put to paper, Cyril and George would spend the better part of three months driving the rural roads and narrow highways between Montgomery and Jacksonville.  Circuits consisting of individual componants would be carefully constructed and tested at their engineering benches at WVOK and WBAM.  The completed sections of the future WAPE transmitter were then carefully boxed up and driven to Orange Park for assembly. Bill had always had a love of aviation; an interest also shared for a while by his brother Cyril.  As deadlines became shorter it became necessary to press Bill’s airplane and piloting skills into service for an express delivery or two. As the brothers worked more feverishly towards bringing the station to air, the day-to-day burden of construction became so great that Cyril moved his family temporarily to Orange Park. 

WAPE's transmitter under construction; 25,000 watt configuration.

Back view of WAPE transmitter under construction; 25,000 watt configuration.

All told, the initial construction of the 25,000 watt transmitter at Orange Park took roughly three months. Unique features filled the spaces behind the anodized gold panels.  One of the most prominent was underneath the giant Machlett ML-5681 carrier tube; an outstanding piece of custom machine work.  Coiled eight inches in diameter with a white ceramic coating, was a bifilar choke which would provide critical electrical isolation for proper operation of the grounded grid circuit.   It was the father of Cyril’s childhood friend Edna Rockwell who custom built this and other large coils in his machine shop in Fairhope, Alabama.  Similar coils were manufactured by Mr. Rockwell for the transmitters at WVOK and WBAM.

Powering Up for the First Time

Once the final component was installed, it was time to bring the newest Brennan to life.  Before the switches could be thrown to supply power to take the transmitter to air for its maiden broadcast, the matter of dissipating the massive amounts of heat generated by the 25,000 watts of radio-frequency had to be address.  Water began to enter the circulation pumps as they were primed to begin circulating the cooling water through the inner workings of the transmitter, around the high-voltage power tubes and through the gleaming white cooling pipes which led outside to the bottom of the cooling pond in front of the newly landscaped building. 

In the days before fully solid-state circuitry, it was a process to bring a high-power transmitter, like the Brennan, to full throttle. First power had to be slowly applied to warm the filaments of the tubes.  The current required was so massive that it had to be increased in stages.  Failure to do so would cause a flashover – the equivalent of an electrical arc fire – ruining all the work which had been done.  Only after the filaments had been eased up to power could the voltage to the plates of the massive Machlett tubes be supplied to bring the transmitter to life. 

The two towering tubes in the final stage of transmitter were set to go with 220 amperes of current flowing through their filaments.  To give you an idea of the scope of current consumed, a typical two-story family home is wired for 100 amperes of service to run the whole house.  The WAPE transmitter had two tubes in the final stage each consuming more than twice that. 

 All systems were green.  Cyril threw the final switch to begin supplying the voltage to the plates of the tubes.  Unexpectedly, the room lit up like a star!  But the sudden flash was not from a fire.  Engineer Don Woollard recalled that “there was blue corona running around the safety screens behind the transmitter like crazy.”  Cyril finally would solve the problem with some supression componants on some of the circuits and fuses in the high voltage stages of the transmitter. 

Once again, it was time to try to bring the transmitter to life.  As the voltages began to flow once agian through the circuitry, excitement again turned disappointment as the Brennan failed to come to life.  After painstaking months of designing, building and modifying the circuitry for the grounded-grid Doherty circuit, Cyril’s relocation of his family from their home in Montgomery to temporary quarters near the new station and over three months of non-stop work Cyril, George and the others on the transmitter crew were disappointed and spent. 

It was time to regroup.  Preliminary measurements, circuit breakers, fuses and connections were rechecked.  Due to the nature of its circuitry, an oscilloscope was required to tune the final stage of the transmitter.  When all other check-points were okay, it was decided to recheck the tuning of the Doherty amplifier.  Preliminary power was again applied to the amplifier of the Brennan.   Three variable condensers would help the crew double check the tuning in three critical stages. First, the phasing (the relationship of the voltages in degrees) between the plates of the two tubes was rechecked.  All was confirmed “okay” by the oval pattern on the green screen of the scope.  The next step would be to adjust the tuning of the voltages going to the plates on those same tubes.  A diagonal line going from the lower left to upper right of the scope indicated that the tuning was not at fault.  Finally a check of the phasing between the grid-bias voltages in the tubes was confirmed.  Once again, an oval on the green cathode ray display indicated that all should be okay to increase the electrical power to bring the Brennan to life.  But it was to no avail.  An initial rise in power led to a shut-off and all was silent except for the circulating pumps and cooling fans.  All things considered, Cyril decided that it was best to take some time and head back to Montgomery to regroup. 

Within a few days Cyril was on his way back down to Jacksonville.  In 1958 there was no Interstate 10 to connect Montgomery to Tallahassee and then on to Jacksonville.  As he made his way from Eufaula, Dawson, Albany, Tifton and Valdosta, along seemingly endless highways which connected the towns, the tuning issue with the WAPE transmitter continued to confound him.  This was the third high-power Doherty transmitter that he had helped to bring to life.  The only major modification was the grounding of the grids, which should have made the transmitter easier to tune and operate.  The design checked out.  All componants were in order and had been double checked.  There were no stray connections, shorts or ground wires.  Even the oscilloscope confirmed that everything was okay and should be working properly.  But, what if the oscilloscope was wrong?  It had not occurred to him or anyone else on the crew that the problem was not with the transmitter, but with a piece of equipment meant to align the tuning.  One could not fault Cyril if the remaining ride to Orange Park was made at a more brisk pace.  He breezed past the crews working on putting the finishing touches on carpentry work to rush back to the area where the gold-iodized panels of the Brennan waited to confirm his hunch.  A quick look at the scope and its inputs confirmed that he was correct.  The wrong type of oscilloscope had been used in the initial set up of the final stages of the amplifier.  A new and correct type of scope was soon found, George and the crew got back to work and the transmitter was soon operational.

The Vulcan “Tower of Strength”

It goes without saying that a radio transmitter is useless without a tower to broadcast its signal.  Without a proper antenna to dissipate the huge amounts of radio frequency energy generated by the 25,000 watt Brennan, the transmitter would in effect shut itself down before a melt-down occurred.

Behind the Radio Country Club, a 299 foot radio tower would send the WAPE signal up and down the coastal states of the southeastern United States.  The operating specifications of the tower were designed by Billy Benns.  Topping the tower off at 299 feet allowed the station to avoid the expense of lighting the tower, which fell one foot below Federal Aviation Administration structural guidelines. 

Responsibility of the constructing the tower would go to the Vulcan Tower Company of Birmingham, Alabama; a company which was owned and operated by Bill Brennan and Billy Benns.  Vulcan was formed in 1953 and built the towers for WBAM.  Most notably, Vulcan was the contractor of record to build the proposed massive WSLA-TV tower in Selma, Alabama.  The Brennan/Benns-owned TV station (Deep South Broadcasting/WBAM) had applied for FCC and FAA approval to build the tallest transmitting tower at that point in time, 1873 feet.  The metal for the WAPE tower was to be fabricated by Sherwin-Moore Steel Company and shipped by truck from Birmingham for final assembly at the Orange Park site. 

The fabrication yard at Shirwin-Moore in Birmingham - WBAM tower under construction for Vulcan Tower.

Ready for inspection

With the transmitter operational and the tower complete, it was time for the Brennan’s to have the FCC inspect and approve the design, construction and installation of the transmitter and other equipment at the Orange Park site.  Cyril placed a call the FCC field office in Miami.  Arthur Gilbert, head of the Miami Field Office, answered the phone.  Gilbert told Cyril he would be up to inspect the station in one week.  Before hanging up, he added that “there wasn’t one of these things that I couldn’t find something wrong with.”

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One Response to The “Brennan” – The Power Behind WAPE

  1. John Ferree says:

    Wow,
    Nice work, David. One thing I most remember vividly about the transmitter was that you could stand in front of it holding a 4′ florescent tube in your hand and the thing would light up and the light would dance with the music! Made a wonderful impression on visiting family and friends.
    John Ferree – WAPE 1967 – 1972

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