HPM’s “Old Betsy” is Made New to Wow the Crowds
Back in the day — prior to 1989, to be more specific — ARRL tours were treated to a demonstration of League Co-Founder Hiram Percy Maxim’s rotary spark-gap transmitter, “Old Betsy.” The vintage transmitter, on display in the lobby of the Maxim Memorial Station W1AW, sustained some damage, however, and she has remained silent for nearly 24 years. Until now.
“It’s always been my intention to get Old Betsy working again,” explained W1AW Station Manager Joe Carcia, NJ1Q, although we won’t be able to demonstrate it during routine ARRL/W1AW tours. Seeing that next year is our Centennial, I made her functionality one of my priorities.”
For Amateur Radio newcomers, a spark-gap transmitter is pretty much as it sounds. A very high voltage is applied to two electrodes sufficient to cause the electrons to bridge — or spark across — the gap between them. Various circuits, and the antenna, are used to tune this broad-spectrum energy — essentially a radio signal (think power line noise or interference from the vacuum cleaner) — to a particular radio wavelength. An improvement on this basic concept was the rotary spark-gap transmitter, where a motor rapidly turns a number of electrodes (Old Betsy has four) past stationary electrodes. This helps to generate a semblance of a “note” on the Morse transmissions in that era before receivers had circuitry to make CW sound as it does today. Old Betsy is considered a non-synchronous rotary spark gap, Carcia points out, and the belt-driven rotor spins at approximately 2500 RPM. The rotating and stationary electrodes are housed within a handcrafted wooden box with an open top.
Back in Amateur Radio’s olden days — the 1920s — Maxim, also known as “HPM,” had Old Betsy installed in the basement of his Hartford, Connecticut, home and keyed it from his operating position upstairs on the first floor. A spark-gap transmitter can generate a lot of noise — both ambient and throughout the radio spectrum — so keeping “Old Betsy” and the operator on separate floors made good sense. The transmitter is equipped with an RF ammeter to measure the RF current flowing into the antenna, although one is no longer connected.
Carcia says Betsy once again is ready for prime time, although it’s been decided not to demonstrate the venerable transmitter for ARRL Headquarters and W1AW tours. “I’ve repaired Old Betsy — and placed a protective polycarbonate shield around her as well,” he says. “Old Betsy is now functional.” But it will only be run without an antenna. The FCC banned spark transmitters in the 1930s.
In its pre-1989 incarnation, the Morse key was in series with the 120 V ac primary of the high voltage transformer, placing line voltage in the open, on the knife switch and on the key. Safety in mind, Carcia designed a 12 V dc relay system and triac keyer, which allows for low-voltage keying of the transformer primary. “The knife switch and key see just 12 V dc,” he notes. “It’s also remote, in that the keying is handled away from the transmitter proper.”
Carcia says the big repair involved the high voltage “condenser,” which we now know as a capacitor. “The center stud, which is one side of the condenser, was broken,” he explained. “I had to disassemble it, replace the stud, and reestablish its connection to the condenser.” The motor that drives the rotary part of the gap also needed to be cleaned and the windings checked. The motor is not the original but one of similar vintage, donated by Mike Castellano, KM1R. “The rest was merely rewiring Old Betsy to her pre-1989 condition,” Carcia said modestly.
Now it’s possible to fire up Old Betsy and use the key on HPM’s roll-top desk to send code. An old fashioned knife switch turns on the transmitter. The unit may be available for demonstration on special occasions.
“When she is running, you can carefully look at the blue spark generated by the keying. A modern LED light flickers with the keying,” Carcia said.
Carcia acknowledges Hal Kennedy, N4GG, for his suggestions during the restoration. “A few years back, Hal assembled his own spark-gap transmitter, using some aspects of Old Betsy as a model,” Carcia said. “His is called ‘Blue Lightning.’”