[Amps] MTBF - was Ameritron Amps

[Peter Chadwick]

Tom,
You've just provided 'Reliability 101'.
MTBF is a figure often bandied about, but without the correct assumptions, numbers and inputs to the equations, can be very misleading. For example, the MTBF of a tube amplifier with tubes changed on a time basis can be very different to the MTBF if tubes are run until they fail - unless you count tube change as a failure, in which case the MTBF is much lower. Back in the days of aircraft radios using tubes, one company at Heathrow paid the service techs on a piecework basis - they got so much per radio fixed. So the first thing they did when a radio arrived on the bench was to change every tube, whether it needed it or not. Thus those radios showed a horrendous MTBF on tubes....
Another complication with electrolytics is the 'memory' - use a 450 volt part long enough at 250, and putting 450 on it gets an enormous leakage until it's reformed at the higher voltage.
73
Peter G3RZP