Zenith 4-tube hybrid Chromacolor questions

[Jon A.]

Originally Posted by old_coot88

Nein, Nyet! No need to ground it. Simply hold the screwdriver by the insulated handle. The arc is drawn by the innate capacitance of the screwdriver 'free floating' in the air. The screwdriver is in effect 'grounded' capacitively to RF.
Though this reactive capacitance is very small, the arc occurs because it's driven by high level RF spikes (the 'fly-back' spikes).

I b'lieve maybe you're thinking of grounding a CRT to discharge it.

Hm, I didn't know that a screwdriver that isn't wired to ground could cause an arc at all. I was thinking of the screwdriver being held close to but not actually touching the HV lead.

[old_coot88]

Originally Posted by Jon A.

...I was thinking of the screwdriver being held close to but not actually touching the HV lead.

That's exactly what you do with the ungrounded screwdriver. Once the arc is struck, draw the screwdriver slowly away and see how long of an air arc it'll pull.
Remember this is RF. No air arc is possible with rectified (DC) high voltage.

[Jon A.]

Originally Posted by old_coot88

That's exactly what you do with the ungrounded screwdriver. Once the arc is struck, draw the screwdriver slowly away and see how long of an air arc it'll pull.
Remember this is RF. No air arc is possible with rectified (DC) high voltage.

Ah, gotcha.

[zeno]

If the damper socket looks fried they went left & right on these.
Part # is 78-1888-01 . Also the big disc cap under it often burned.
To replace with any 12 pin Zenith socket drill out the center rivet,
remove unused pins & the 2 mounting pins. Remount with old
grommets & rivets since you will never find them.
If you have 700 V plate odds are tripler or damper. FBT's never
went on theses. Only changed one out of what must have been
over 1,000 I worked on. It was a BIG kit.
Jon is correct, the chassis # often stamped by HV adjust control.
When done clean the mung from the anode, it will arc on the first
humid day.
Always nice to see my old "friends" being worked on.

73 Zeno