[Milsurplus] BC-611 power

[J Forster]

 john p hutchins wrote:

  Hello All -

  Well hate to be a project killer Royal Signals has a simple
  inverter/converter see :
  http://www.royalsignals.org.uk/photos/inverter.htm
  I like the addition of the reed relay that senses Filament current and

  turns on the HV inverter.

I worked on that design with Keith and suggested the rewound reed relay.

BTW, the relay turns were determined by trial and error. Pick a wire
size big enough to carry the filament current at 500 Circular Mils /
Amp, remove the existing winding, and fill the bobbin, then test to
measure the pull in and drop out currents. Add or remove turns to get
those currents roughly centered around the filament draw. Radio Shack
had (has ?) suitable relays for about $2. With the relay, the thing can
be put in a box and labeled to look like a A B battery. The battery
drain is zero with the filaments off.

I don't much like the astable MV as a drive for the inverter because
waveform symmetry is not guaranteed. Hence my suggestion of a 555 and
flip-flop in an earlier post. If the transformer drive is asymmetric,
there will be net DC flowing through the primary, possibly leading to
saturation. It also wastes battery power.

Also, I would have preferred a commercially available transformer with
wide availability.

Keith certainly did a nice job on the unit, but IMO the above changes
would improve it.

FWIW,
-John