On the expanding area of glass? Is inside of expanding area metal?


Yes, the anode cap is connected to a conductive layer on the inside of the glass envelope. It is a thin conductive graphite layer called aquadag. Electrons accelerated from the cathode exit the cathode ray tube here.
Both inside and outside of the glass envelope are conductive - it forms a capacitor which is the final filter that ensures that high-voltage is relatively constant, with small ripple.

The outside conductor on the glass envelope must be grounded for your protection.three-cathode C.R.T. connections

  • \$\begingroup\$ +1 There is often no conductive aquadag on the outside of small CRTs (oscilloscope, radar etc.). On larger tubes the built-in capacitor from ground to 2nd anode can provide an unwelcome surprise in the form of a jolt if it's charged and comes in contact with fingers etc. \$\endgroup\$ – Spehro Pefhany Apr 3 at 19:08

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