We are KILLING our HV diodes...?

Now that I have your attention <grin> I thought I would pass on a warning I
received from an Electronics Engineer this morning:
--------------------------><-----------------------------------------
To: <jrr@flippers.com>
Subject: Grounding picture tube

I've seen your pages about handling video monitors.
However you're very secure and precise with this there is one thing
you forgot to mention.
You should NOT ground the anode of the tube DIRECTLY to ground.
ALWAYS use a resistor of 1 Mega ohm between earth and anode.
Direct grounding can cause the cascade rectifier to die.
Using 1 meg won't affect the discharge at all and will completely
discharge the remaining high tension.

Yours sincere.
     Hans Balk
(electronics engineer)
-------------------------------><-----------------------------------
Hans here has raised a good point and this might explain why the B&Y XY
monitor HV diodes are failing-'cause we are killing them! @!#$!@#$@.

I have asked him to elaborate a bit on the theory behind this , but in the
meantime, might I recommend that you all follow his advice? Also to get a 1
meg diode to do this job, remember that we are dealing with 12 - 24KV here,
so a regular 1M 1/4 watt resistor won't cut it. It will arc over
internally...use a series of ten 100K 1/2 watt resistors (2Kv4 max. across
each??), insulated with a couple of layers of HeatShrink, that is about ten
or more inches in length. This is just off the top of my head, I suspect
that this design is not quite right yet, perhaps twenty 50K resistors (1Kv2
across each) is better...there are special HV resistors, scrounge around...

If you have an stand-alone HV meter probe, so much the better, allow it to
discharge the tube...

John :-#)#

  John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
  Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
  http://www.flippers.com
         "Old pinballers never die, they just flip out."

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Received on Sat Apr 22 11:14:14 2000