THE GREAT MULLARD MAGIC BLOG — mullard crt

A number of tests were undertaken on the finished CRT under actual operating conditions, below, we shall discuss each of them in turn: - Cathode emission -  insulation resistance between all electrodes was checked, anode current, Ia was checked as was "cut off" which is the negative grid potential required to nullify emission Vacuum integrity - the degree of vacuum was determined using an ionisation gauge. Final visual check - the focus was checked, the raster was checked, the faceplate was checked for any blemishes, unevenness of colour or stray emission, the whole tube structure was checked for mechanical defects.  Only then was the...

 After exhausting and capping, the tubes were fitted with their bases and still in their linen bags, were transferred onto a conveyor belt where each tube was plugged into an adaptor which supplied the appropriate voltages to the heater, cathode, grid and first anode as well as a heat from an embedded element which baked the cement inside the base cap thus hardening and attaching the base to the bulb neck: - After heating and as power was applied to the tube, the heater fired and cathode emission commenced and this initial 'firing' reduced a part of the cathode...

Well, it's been a long journey, having inserted the electron gun, withdrawn the air from the bulb and sealed it off, the only remaining thing to do is to perform that final process of "ageing" and a Mullard Cathode Ray Tube was available for sale.   More deatil on this final process in my next blog entry but for now, I just wanted to share with you this evocative photo of tubes being aged - don't they look cute in their Moygashel linen bags.   As we all know, linen from Maigh gCaisil (the place where the stone fort is)...

The electron gun we described in a previous blog entry was mounted and sealed into the neck of a tube using an automated machine which comprised of a number of fixtures which moved around the carousel and revolved on their own axis.   At the first position, the tube was mounted top downwards in the top part of the fixture and the electron gun was mounted base downwards in the lower part of the fixture .    In the following photo, you can see the loading arrangement: -  Operation of a lever moved the gun such that it entered the neck of...

Well, this is what an electron gun looks like: - It comprises of an indirectly heated cathode, a grid and two anodes.  The inner anode is maintained at a positive potential of up to 7kV on these early electron guns, yes, really!   Let's now look at the bits and pieces individually but first, an exploded diagram: - The cathode assembly - this comprises of a short nickel tube, one end of which is closed by a disc coated with an emissive admixture of barium and strontium oxide. The heater, which comprises of a spiral tungsten wire coated with an insulating...