Dominic-Luc Webb wrote:
> I am after high voltage (for photomultiplier tubes) and considering
> use of TV flyback transformers. I have a couple, including some
> "known good" specimens that were extracted from working TVs.
> I am able to find windings (2 sets, I suspect) on the base pins that
> certainly must be 2 primary coils. Using an Ohm meter and checking both
> polarities, I do not find a return for the high voltage output (red with
> suction cup), or the two ouput wires coming from the side that I suspect
> are somewhat lower HV (horizontal and vertical control, 10 kV ???).
> Is there some nice trick to identify the HV return, or should I try to see
> where I can generate a sparc from the remaining pins that are not primary
> leads? Should this return be common to all three HV outputs? As I mention,
> I want to power PMTs, so even 10 kV is escessive for my needs.
> Dominic
If the suction cup lead is included in your resistance measurements,
then a high voltage rectifier (several silicon junctions in series)
are also included. Your ohm meter probably does not contain a high
enough voltage source to forward bias this string of diodes to
indicate approximate coil resistance. Add a couple 9 volt batteries
connected together in series and use the milliamp meter to find out
which low voltage winding is also connected to the high voltage output
(positive) lead. You will need to connect the negative side of the
battery to the the suction cup to forward bias the rectifier, since it
is designed to produce a positive output voltage (and block it from
going back into the coil).
Unfortunately for you, PMTs need a high negative voltage with respect
to the near ground output. So you will either have to find a flyback
that has a diode that can be reversed, or has the diode external to
the flyback transformer (rare these days).
--
John Popelish
