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Title: Quadrature Filament Excation of Gaseous Rectifiers Post by: k4kyv on March 02, 2009, 07:50:08 PM I ran across this interesting bit of information regarding gaseous tube type rectifiers; presumably this applies to both xenon gas rectifiers like the 3B28 and 4B32, as well as gaseous mercury tubes like the 866-A and 872-A. This is the first time I had ever heard of this, and I am passing it along FWIW.
Both RCA and Tung-Sol recommend "quadrature excitation" of the filament for obtaining the longest tube life. In quadrature operation, the filament current is phased to be at a minimum when the peak anode current flows. This means the a.c. voltage source supplying the filament transformer should be 90° out of phase with the source supplying the plate transformer. This does not change the full maximum ratings of the tubes, either peak current or peak inverse voltage, but its benefit is to maximise tube life. From the RCA data sheet on the 3B28 (xenon equivalent to the 866-A): Quote The filament-supply voltage for the 3B28 may be either in phase or out of phase with the anode voltage. With out-of phase excitation (quadrature operation), improved utilization of the cathode is possible. Although the 3B28 carries no higher anode-current rating for quadrature operation than for in-phase operation, quadrature operation is conducive to appreciably longer tube life. For optimum results, the filament and anode voltages should be 90° out of phase. In practical applications however, nearly full realization of the advantages of this type of excitation is possible even when the phase difference between the filament and anode supply voltages ranges from the optimum value by as much as ± 30°. In polyphase operation where the anode voltage shifts from one phase to another during the current-conduction period, quadrature operation is obtained when the filament voltage passes through zero at the center of the current-conduction period. Title: Re: Quadrature Filament Excation of Gaseous Rectifiers Post by: Opcom on March 02, 2009, 11:22:31 PM Do they say how much life might be gained? It makes sense for rectifier running high peak currents, seems like an uptime tweak.
Title: Re: Quadrature Filament Excation of Gaseous Rectifiers Post by: WA1GFZ on March 04, 2009, 09:09:19 AM sounds like marketing poo AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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