At 15:44 08-07-14, you wrote:
You are so kind. Thank you very much.
My tubes look exactly like 4B/551B(D). I will measure the dimensions
to be sure as soon as I can.
It looks convenient that the filament voltage is the usual 6.3 volts.
Interesting is that they count with anode voltage as much as 10 or even 14 kV!
Thanks again for your effort.
73, Petr, OK1FIG
They look like switch tubes for magnetrons, so the anode voltage may
be very high.
Good... it may be an interesting job :-)
73 - Marco IK1ODO