[morzh]

I tried. This would not be the first time, I have one like that in my Zenith 9S262, and this is why I knew.
But in that other one the wire protruded, so I was able to solder it (though had to be very gentle when pulling the grid clip off).
In this one it is somehow under the level of the hole, when I sucked the solder out. Not sure how it is even possible. Could be that it got broken of first, a little piece embedded in the solder on the cap, and then when I took the solder off, the remaining stub no longer protruded.

So...I keep the tube, it tested good when the connection was there - maybe I will come up with some crafty stratagem to solder the cap.
Actually I thought of one - I will try to press around the hole to make the flat surface a funnel thus lowering the level of the hole, and maybe that could create just enough protrusion for me to try to solder the stub.

Well, luckily I did have the tube (the reason was that very detached cap in my Zenith - bought it just in case....came handy!), so I replaced it.