[ARC5] Transmiitters: Parameters?

[Mike Morrow]

By my error, my earlier post was sent out incomplete.  The intended post follows.

Dennis wrote:

> The configuration as manufactured  produced the required output power
> and two tubes would provide a measure of increased reliability (and
> peace of mind as well...).

Two PA tubes in parallel provide little to nothing in advantages for reliability.  A mechanical element failure within either tube will almost certainly result in complete stage failure, short of simple connection loss at the base.  Likewise, the most common tube failure is an open filament.  The series-connected PA tube filaments then produce total PA stage failure.  Envelope failure in one tube with total vacuum loss will result in filament failure as well.  Thus, any argument of redundancy fails any postulated probable individual tube failure,  In fact, using two tubes doubles the probability of stage failure from these faults, compared to a one-tube design.

An argument for the two-tube design could be made based on two tubes performing as one larger tube.  At the desired design PA stage power, that would reduce long-duration stress by reducing plate and envelope temperatures and prolonging cathode emission lifetime, compared to a one-tube design.  Still, the PA stage more than meets CCS specifications, even though the nature of command set duty would seldom stress even a single-tube design.

IMO, the two-tube PA design is certainly NOT based on increased reliability (which is actually significantly lowered), and is more probably based on both long-term tube life and some level of increased power output.

Mike / KK5F