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Old 02-07-2017, 08:07 AM
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dtvmcdonald dtvmcdonald is offline
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Join Date: Nov 2012
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Yesterday I thought of a different test for internal wire breaks or shorts
in a CRT. Its best if the neck is clear of yokes/purity coils, but can be done in place.

I hooked up a 1 MHz signal generator, 25 volts, to each pin of the CRT in turn.
There was an aluminum foil shield, grounded to the purity coil, taped to
the bakelite tube base.

I used a high impedance scope probe and moved it around,
observing the pickup.

I expected modestly good symmetry about the three guns if
all elements were as expected, and a smaller pickup near an element
that had, for example, a bad pin connection. All was as expected if
good connections.

I then found some #6 wire and cut off a 1 inch piece of that,
connected it to the generator, and taped it to the outside of the
tube base, lying parallel to the suspect red screen pin. The pickup on my scope
was, again as expected, still there but down by a factor of
four to six.

So its official, my tube has poor red emission.

Also .. playing with the blue and green screen controls
shows that the higher they are, the lower the tube gamma.
And I had noticed that over time my sets gamma seemed to increase ...
the blue and green screens had been turned down as the red
got weaker. Thus I think it was not necessarily a one-off disaster, possibly.
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