On 21 May, 20:09, Gary Tait wrote:
wrote in news:1179684751.540124.182250
@z28g2000prd.googlegroups.com:

These VFDs typically want +30v for the anode,

IME, the filments are grounded, with the segments pulled to ground ot -30
as needed.

VFDs are matrixed thermionic valves, and you cant run what is a valve
mechanism like that. Which bit is grounded doesnt matter, but always
the anode is positive wrt filament to light it. At only 30v anode the
grids should be positive to get light output.

In practical apps the segments are matrix driven, lit one after
another, so you need to scope it to see whats going on.


and filament v depends
on the display, but is very low. They can dim after 20 or more years
of use, if its that old I'd suggest a slight filament boost. One way
is to put a turn or 2 onto the mains transformer secondary and connect
this in series with the filament feed.

If the trasnformer is open framed.

If its not one can typically tweak the filament supply cct to get a
bit more V.

But I see this is only 10 yrs old. It may be the display is being
overdriven, which causes them to dim prematurely. If so, removing the
usual dark filter and replacing with something lighter, or possibly no
filter, would enable reduced anode current.


NT