Ken Beckwith saw our article about key management and shared an approach that may help fellow broadcast engineers.
Ken purchased a CD/DVD case and stripped out the sleeves. He bought some Velcro brand hook-and-loop fasteners and lined the case with the “loop” half of the tape; he then placed the “hooks” side on the backs of station key tags, labeling the fronts with call letters and other pertinent information like security system entry codes.
Ken keeps the case in his vehicle, secure and out of sight.
His suggestion is a good one, especially for contract engineers who deal with lots of keys. When I was contracting I used a plastic mic case with the keys just tossed in the case. Ken’s tip keeps your sets organized so you are able to make sure that each client’s keys have their spot in the case, less likely to get misplaced.
DIY tank coil
David DeSpain, P.E., worked at CBS Radio’s KMOX in St. Louis in the 1970s. At the time, the station used a Westinghouse 50-HG transmitter, with push-pull 5973s, modulated by another pair of 5973s, also in push-pull configuration.
The transmitter’s plate tank coil was made of silver-plated 1/4-copper tubing, but it always ran hot.
Chris Sarros W0SAP, Murrel Perry W0QAC, Jim Scott and David replaced the tank coil with 1/2-inch copper tubing. They formed the coil around a welding gas cylinder of carbon dioxide (used for the fire suppression system). Bill McCarren from CBS Network Engineering in New York assisted, using the first Hewlett-Packard HP-35 calculator David had seen.
Bill designed a replacement for the low-pass “T” network and impedance-matching network. The original tank coil had a link-coupled output, and this was copied for the replacement. The new network that Bill designed consisted of two low-pass Pi networks, with each successive “C” leg to ground also being series-resonant (via a very small coil at the second, third, fourth and fifth harmonics).
David reports that it worked like a charm and tuned up with no problems. The new coil put an end to the overheating.
The same transmitter also would “fuzz up” the audio. It wasn’t heard on the air but was audible on the modulation monitor. A scope showed the “fuzz” to be approximately 32 kHz.
David showed them how to use a signal generator with a 10 k-ohm resistor in series with its output, and a scope for a detector, to search for resonances. They found the problem to be the PA grid tank coil resonating with the bypass capacitors. David doesn’t take credit for the cure; he believes it was Jim Scott who came up with the simple idea of doubling up one of the bypass capacitors. The “fuzz” was never heard again.
By the way, David donated the left PA plate current meter, which normally read 3.15A, to the Texas Broadcast Museum in Kilgore, Texas.
A fortune in engineering
Jerry Snaper, KG6FDM, is a retired chief from KVMR(FM) and KMYC(AM) in California. After dining at an Asian restaurant recently, Jerry opened his fortune cookie to read a message that relates to our engineering efforts: “The expedient thing and the right thing are seldom the same thing!”
Truer words have never been printed.
Technoguy tip
Michael Baldauf, a fellow Radio World contributor known as the Technoguy, is a semi-retired broadcast engineer in southern Colorado.
He notes that the nuances of analog audio can be overwhelming, especially if an installation demands the perfect interface between balanced and unbalanced signals, various audio levels or different types of connections.
He calls our attention to the ARTcessories CleanBox Pro. It comes in several variations.
In his photo, unbalanced RCA inputs from the studio are interfaced to the balanced XLR outputs for the audio chain, and the 1/8-inch unbalanced stereo output is used for the streaming computer. Two small controls on the front set the levels individually for balanced and unbalanced outputs.
You can set audio levels quickly using the level knobs, rather than muddling through menus and configurations of the various devices to which it interfaces. It is also good for quick setup and matching to equipment at venues where a temporary sound system is needed. You can accomplish quick matches between devices that may only be configured to work together for one event, rather than building custom cables.
It is sold by broadcast equipment suppliers and companies like B&H Photo Video; we see it online for under $90.
Apologies to Sheldon
Strive as we do to guard against typos, they creep in. In our May 22 column we mentioned Sheldon Daitch, a friend and contributor to Workbench, but we misspelled his last name.
Sheldon, now retired, remains a fan of the Western Electric 111C audio transformer. He provided a link to David Gleason’s awesome World Radio History website to download a copy of the Bell Labs Transmission Transformers Application Note, which includes data, index tables and pictures of the transformers. Click here to scroll to find “WE-Transformers_1958.pdf.”
Workbench submissions are encouraged and qualify for SBE recertification credit. Email johnpbisset@gmail.com.
