WHAT'S INSIDE A VALVE (xi)

Let's chat about SCREENING CAGES today.   This is a natural progression from yesterday's topic of METALLISING as recent valve designs tend to use SCREENING CAGES instead of an external metallic coatings to prevent outside magnetic and electrical fields from interfering with a valve's normal operation.  

Screening cages usually comprise of a wire mesh cylinder which completely encircles the electrode cage.   The cage functions as an electrostatic shield by preventing external field interference and additionally serves to collect stray electrons that may escape from within the electrode cage, this is also economically beneficial as there is then no need to INTERNALLY CARBONISE the envelope.

So, now you know why EF86 don't have any INTERNAL CARBONISATION and you may have also realised that many sellers on EBAY erroneously peddle their EF86 as having a 'pin mesh anode'  - and they are  wrong - what they should say is a 'pin mesh screening cage.' 

So here's a salutory lesson, don't buy from an EBAY wide-boy who knows nowt but from a webshop wide-boy like me -  Mr Mullard Magic who knows just that little bit more.!!!!!