Help with Heathkit IO-4510 O scope

[Murray Grandy]

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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