One of the problems I have working with the Six Dial DX-6 resistance device is that if I use it with researched Rates, like the Coppen or Delawarr rate books, it seems to remove the element of tuning the “trend” with the stick pad. The dials are set to given numbers and that’s that. But since I learned on a Hieronymus Machine, I’m accustomed to the “human element” as an integral part of the system – the “element” being my nervous system.
The idea is also to allow a set of Rates – the “trend” – to be customized to the operation at hand, and I’ve come to believe that this is especially crucial with resistance-based devices. Or at least if one is going to use repeatable dial settings. Dr. Hieronymus considered resistance-based devices to be problematic; even high quality potentiometers are only accurate to within +/- 5% of their rated value. In my builds I went through several wire-wound potentiometers and tested them for accuracy, and used the ones that most closely matched their ratings. But even still the ranges were only within +/- 2%. And still, when you set a pot to a particular point on a dial, the next time you set it to that point, it may be off by a few percent from the last time. The wipers inside that make physical contact are not accurate enough.
Air-tunable capacitors, on the other hand, use interfacing layers of rotating metal plates, separated by a small gaps of air. There is no metal-on-metal contact, so capacitance is dependent only on the positioning of the plates, which with a fine enough dial scale, is very repeatable (this is why they were used for the tuning controls in radios.)
So, I decided to use the same method used to fine-tune loop antennas, of inserting a air-tuned capacitor across the terminals. Generally, a screw-adjustment trimmer capacitor is used for radio devices, since the radio is typically made to work with a fairly narrow bandwidth, and once it’s set, it’s locked in (again, air caps are very accurate and stable. As Doc Hieronymus once said, unless you hit it with a hammer an air cap is not going to malfunction.) But I wanted a wide range and manual tuning, so I used a Bakelite radio dial from a vintage crystal tuner, and the same type air capacitor as used in the Radionic Analyzer.
So now I have a way to use Rate books with my Three-Dial and Six-Dial devices, and still be able to tune it accurately for transmission of Aetheric signals.