Saturday, March 4, 2017

50Hz VFD filament drive test

applies to the 16ohm cold filament cathode (i don't have the warm data yet) just the beginnings
an attempt to decide whether to use sine or square-wave drive
- though the overall efficiency for this circuit is below 10% - then right now i keep preferring it
- simply coz setting up a consistent pulse drive is a way more complex (unless you have a separate supply to drive the pulse TF from)
- still the peculiarity of the desired output (center tapped winding) sets extra requirements to this drive (you actually can't drive it from the single switch reliably for balanced output or then making it reliable seems at this point more complex ((error prone in practice)) than using a sine-wave drive)

anyway what we got

PS! reproducing the TF in practice is not so straight forward coz of speculative winding resistances
(winding resistances usually are orders of magnitude lower than the corresponding impedances - so we likely shouldn't care) but here the R.primary much affects a lot of "operationals" that have to fit !optimally&practically for 6LR61 - this in turn requires to redesign the secondary winding -- is quite lengthy error trial chain + in addition to confirm/re adjust in practice (possibly start the design over and over again . . . !!!)

+ did some quick static measurements on . . .

Gate voltage+9V+9V & *more
Anode voltage+18V2× +9V & *more
Filament current
DC-driven to neg. from GND
Anode brightness adjustment
► increase voltage for edge segments ◄
not required for parameter values shown aboverequired by unknown factor
► required less for gate , anode voltages *exceeding the ones shown above

if you increase the AN GT voltages the filament feed may be lesser but there seems to be a threshold A-G voltage and filament power starting from where the fade left/-right is reduced and the seeming symbol brightness does not much increase

also - when i experimentally found the FUTABA's operating parameters i didn't expected so high filament current so i had to reduce a lot the gate/-anode voltages to get their apx. min./-normal values -- what was studied is that while the anodes did glow most bright at AN set to 27÷36 V (gate same or 9V less) then going up from there they seemed to start dimming again ?? !!!


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