THE GREAT MULLARD MAGIC BLOG

Some of you may have seen the news report showing Her Maj boating on the Leeds & LIverpool Canal on the broad beam narrow boat, The Pride of Sefton in Burnley.    As she  cruised along, viewing  the old iron bedsteads, shopping trolleys and old tellies in the canal as she passed by, I wondered if these may have jogged her memory and did she then turn to Prince Philip and say, " I say, do you remember when we went to that valve making place nearby?"   Yes, they did visit the Blackburn site and details of this visit...

 It is said that a picture is worth a thousand words so for this blog entry, here we are - a picture which lists some of the valve failure modes discussed below as well as some extra ones:-

Over-running output valves and rectifiers or allowing them to operate at extremely high envelope temperatures, can have another undesirable effect as the valve ages where electrolysis of the the envelope glass can occur.  The electrolytic action attacks the glass envelope in which lead (Pb) is extracted from the glass  as an anion which in turn is then attracted to internal wires having a negative charge resulting in metallic lead deposition around the negatively charged lead in wires -  especially where they enter the pinch or base button.   The effect of these 'Lead lead trees'  - which are often only...

This is an interesting one as a number of insulation failure modes exist for ageing valves.   Often poor insulation may be caused due to cathode emissive material or metallic deposits which have evaporated from the  electrode cage being deposited on various parts of the valves interior.  Deposits can build up on mica separators or the glass pinch where the connection pins/leads enter the envelope and even sometimes the inner envelope glass - remember those manky EL84 which had been run hard and hot and built up those yukky black deposits on the glass.........? In manufacture, the mica separators are...

Well just look at this, bet you have all seen 'phone zombies' like this mooching about and crossing roads without looking.   Nice Sennheiser headphones the lady is wearing and the iPhone looks cute too - very 2017.     You might think this is a new phenomenon but no, you would be wrong as the following picture attests:- Et voila, in 1924,  a young lady outdoors, complete with headphones and a rather much heavier piece of music making kit.    Like I said, nothing new under the sun!!!!