Thomas Meyer’s Tube of the month in October 2016 is: VT 800
Hi!
This months tube is a directly heated transmitting triode, from the RCA 800 series. It is actually the very first tube in that series, the 800 itself.
I have never done anything with that tube and most likely never will. But it is an interesting triode nonetheless and certainly usable for audio applications.
Like most transmitting triodes, it uses a thoriated tungsten filament. In this case with 7.5V and 3.1A. So rather hefty requirements not far off from the 211 or 845. The base is UX4 but only 2 of the pins are used. The filament is supplied through the base. There are two caps on top of the tube which give it a very distinctive look. One is for the plate connection and the other for the grid. This arrangement keeps inter electrode capacitances low which helps for RF applications. The tubes was intended for both RF and audio frequencies. The data sheet lists operating conditions for use as Class AB power amplifier and modulator and for Class C RF power amplifier service. There is a sample circuit of a PP amp with two 800 as output tubes driven by a push pull pair of 45s. The tube was mainly designed for grid current operation but like most such tubes could be used in Class A1 as well.
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