Re: 811a coil/ bad diode?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>" <youngs-at-konnections-dot-net>

Steve,

Yes, Microwave oven diodes are different in that they are a bunch of diodes
in series.  The typical forward voltage drop across one is six to 8 volts.
Usually, this is more than the voltage used in your ohmmeter, so it will
indicate an open circuit even though the diode may be perfectly good.

To test the diode, use a couple of 9 volt batteries in series, or a 12 to 18
volt DC wall wart, connect it to the diode and a 100 or so ohm resistor in
series.  Measure the voltage across the resistor.  Depending on the polarity
of the diode, you will measure either zero volts, or supply voltage minus
about 6 or so volts if the diode is good.  If you measure zero volts for
each polarity of the diode, it is blown open.  If you measure the supply
voltage across the resistor, then the diode is shorted.

--Steve Young

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, July 04, 2002 12:52 PM
Subject: 811a coil/ bad diode?


> Original poster: "Steven Ward by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<srward16-at-hotmail-dot-com>
>
> Hi group,
>
> I think that i may have come across my problem with my small VTTC that ive
> been working at for awhile.  I decided to check out all of my components
> today and found that my diode is not testing good.  It reads open circuit
in
> both directions.  Is this a sign of a bad diode?  I know that it would
> usually be, but are microwave diodes different?  Another diode (suspected
> bad as well) i have reads 4kohm im both directions.  I think i may have
> blown the diode when someone on this board told me that the schematic was
> incorrect.  I followed his directions, and blew a 15A fuse, and was
probably
> quite close to blowing my tube! im sure that amount of power could destroy
> that little diode.  So i followed the original plans and the coil works OK
> giving about 3" sparks at most, with unopredictable performace from time
to
> time. Ive been running the coil for a few days with out realising my diose
> may be bad.  This makes me suspect the diode.  So do i need a diode?  or
can
> i bypass it?  a new diode isnt much of a problem but i want to know it i
> even need it, and if i dont what other modifications do i need to make?
> Thanks,
>
> Steve Ward.
>
>
>
>