[Heathkit] RE: Help with Heathkit IO-4510 O scope

[Mark Graalman WB8JKR]

  Murray,

  Your meter probably isn't testing the diodes properly because it
doesn't have enough voltage acrossed its leads to "activate" the
diodes junction. My guess would be to properly turn on that
diode you'd need about 3 volts to turn the diode on enough to
cause current flow. The connector on the side of the CRT is
the connection for the anode accelerator, you'll get a trace
without it, but it will be MUCH dimmer than normal, and
probably disappear altogether at higher sweep speeds.

73,  Mark  WB8JKR


On Wed, 8 Oct 2003 10:58:05 -0700 "Murray Grandy" <mgrandy at telus.net>
writes:
> Just getting back to working on subject scope. This is a classic
> example of "The more I find out, the less I know".  Received the
> exact replacement 3kv diodes (57-56) from Randy K8TMK. Thanks Randy
> for the diodes and the nice Heathkit catalog. As a few people
> suggested, these new diodes test the same as the old so, I guess
> they can not be checked the normal way.
> To add to the confusion, I have on hand 2kv (NTE525) diodes that I
> purchased from Mouser sometime ago, and they test as usual on the
> two different DVM's diode test. How can there be such a difference
> between 2kv diodes and 3kv diodes. But what is even more baffling
> is, the trace is on the scope without having the 3kv (PDA) lead
> connected. I discovered this by accident, checking the voltages and
> while reaching around the front of the scope looking for the on/off
> switch, there was the trace, and can be adjusted up down etc just
> like it was in it's right mind. So, just what is this 3kv supposed
> to do. It is connected to a large rubber type connector that plugs
> into the side of the CRT just like the old TV sets. I guess I will
> have to read the manual unless some kind soul out there will tell
> me.
> Murray
>

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