Hi Tim,

That is a common 475 problem. They have an electrostatic lens built
into the CRT to give it a large beam deflection with a very small change
in vertical plate amplitude. They use a very high anode voltage to give
you that nice bright trace at high sweep speeds.

Anyway, Tek used wire that has poor insulation for the 21KV anode lead.
The lead is potted right into the tube's anode terminal. Clean up all
the black gook that the anode lead sucked out of the air with isopropyl
alcohol (91%), and coat the offending section of the anode lead with
a good grade of clear silicone RTV...preferably the kind that doesn't
smell like vinegar. Anywhere there is black gook, is where there is a
problem. Corona dope will work too, but it is brittle, and won't take
any flexing.

-Chuck

Tim Williams wrote:
This looks like a "what's your scope?" thread... so who am I to stop
a natural progression in a thread

Tek 475, *free* from a very generous friend (but he has no intention
of returning to electronics). Dual channel, additive, dual trace,
X-Y graphing, sweep up to 1ns/div (with 10x zoom) with two timebases
allowing all sorts of freaky and neat scrolling, zooming, chopping
and cutting of the waveform.
I don't like using it though because the CRT sounds like arcing.. smells
like ozone...