VT100 preventative maintenance?

tony duell ard at p850ug1.demon.co.uk
Sat Aug 22 15:29:09 CDT 2015

> > ...
> > [1] In the UK we call all CRT elecrodes after the control grid (first grid) 'anodes' which
> > makes sense as they are run +ve wrt the cathode.
> So does a UK tetrode have one grid and two anodes?  Or is there one terminology for
>  CRTs and a different one for other tubes?

The second. A Tetrode over here has 2 grids (control grid and screen grid [1]) and one anode. A 
pentode has 3 grids (control, screen, supressor)

[1] An old name for a tetrode or pentode over here is a 'Screen grid valve' Some early valves 
had type codes which clearly came from this For example there was a 'AC/SG' which was 
an indirectly heated (the 'AC' part, meaning the heater could run on AC) tetrode (the 'SG'
part). I have an old Cossor MVS/PEN valve. That stands for 'Metalised' (meaning there is
a conductive coating on the outside of the glass envelope for shielding), Variable Mu
(non-linear, so amplification depends on grid bias) Screengrid (a tetrode or pentode) and
the 'PEN' part means it really is a Pentode.

Also note that we use the term 'valve' for  diodes, triodes, etc, but 'tube' for CRTs, nixie tubes,
dekatrons, voltage stabilisers, probably trochotrons, etc. There seems to be no obvious
reason for what is a 'valve' and what is a 'tube'.



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