[Boatanchors] RECTIFIERS

[J. Forster]

How are you testing them? With an Ohmmeter? If so, your result is not
surprising.

At 14KV PIV, each "diode" is virtually certainly a series string of lower
voltage diodes, perhaps 14 ea of 1 KV PIV units. As such, in the forward
(conducting) direction, you'd see 14 times the typical Si voltage drop of
0.6 V or something like 8.4 V. This would look like an open to a VOM.

Hook up a supply of about 20 V, the DUT and a series resistor (a few K)
and see if curreent flows.

If you measure the voltage drop across the diode you can figure uot how
many diodes are in series.

BTW, there may (should) be large resistors ( a few hundred K typically)
across each diode to equalize the voltage drops in the reverse direction.

Best,

-John

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> I recently had occasion to dismantle an HV power supply which, for lack of
> a better name, I will call "The Widow Maker".  It powered a 3-1000 linear
> at about 3900V and was DANGEROUSLY constructed.  Anyhow, the diode bridge
> was composed of a quad of K2AW 14KV units, all of which, in testing, show
> NO presence of a diode junction.  They are not shorted, they appear to be
> open.  The transformer and caps are both good.  I can't think of a
> situation which would cause all four to open up.  The linear did work for
> the owner (now in a nursing home) at one time.  My impression of K2AW
> products is that they are of good quality and not prone to failure when
> operating this far below their rated voltage.
>
> Anyone care to comment on this?
>
> Bill VE3NH