Only the very best for the Queen !
The "NumiQueen" is a tube clock kit designed around six Russian IV-13 Numitrons. In our opinion, these are the finest numerical tubes ever produced in the 80’s. There is a good reason why the IV-13 is called the Queen of the Numitrons. With its extra large 22mm high digits and a warm orange glow, it is very pleasing to look at and can be seen from a fair distance. Coupled with modern control circuitry, we developed this very unique tube clock kit, the first of its kind using 6 x IV-13 Numitrons.
So what are Numitron tubes ?
A Numitron utilizes eight filaments for the display, seven for the segments, and one for the decimal point, all of which are enclosed in a typical tube glass body. In effect, a Numitron can be seen as an eight-way incandescent globe.
The big advantage of using a Numitron as compared to the more popular Nixie tube is that the Numitron only requires very low control voltages of 5VDC as opposed to about 170VDC for the typical Nixie tube or around 5 VAC and more than 20 VDC for the well known green / bluish VFD displays. Because of these lower voltages a Numitron, such as the smaller IV-9, can be directly driven from the control counter circuits. For this reason there are already a number of Numitron clocks available on Ebay using this smaller IV-9 Numitron.
However using the much larger IV-13 Numitron requires a more complex and powerful driver circuit as each of the eight segments of the IV-13 draws about 32mA of current! Another challenge in driving Numitrons is that they does not lend itself to be easily driven by a conventional Multiplex circuit.
Mr. Nixie’s unique solution and design
The answer to the challenge of controlling the IV-13 Numitron is the Texas Instrument TLC5916 Constant Current LED Sink Driver chip! Using the TLC5916 also gives us some unique and very desirable features:
- Due to the constant current source, each segment of the IV-13 does not suffer from the usual ‘cold start’ inrush current experienced by the filaments.
- This drastically extends the lifespan of each filament/segment in the IV-13 to much more than 50,000 hrs. Because of the harsh inrush current, e.g. an incandescent bulb usually always fails when switched on.
- Each filament/segment of the IV-13 will glow at a constant and identical intensity. Tests have shown that if a conventional control circuit (constant voltage) drives the segments of the IV-13 there can be a variation of up to 20% of the current consumption and therefore brightness of each segment, which would be very noticeable and undesirable in a digital clock if two or more of such different tubes are fitted. By using the TLC5916, each segment of the IV-13 will get its "own" 32mA current irrespective of the voltage level with the result being that each segment glows at an identical intensity.
- One of the drawbacks in using a constant current source is that the reaction time of each segment to come up to its full glow is rather slow. For that reason, once again, we came up with a very unique feature. Each filament/segment is constantly ‘pre-heated’, which results in a very quick reaction time for the relevant segment to turn on when required.