THE GREAT MULLARD MAGIC BLOG — VALVE AGEING

There has been much discussion over the merits and dangers in running up valves using precious valve testers rather than the safer option of using a powered rig for this purpose.   I have delved into the Mullard document archive today and came up with the photo below which shows Willeke Fokkink in 1955 at Philips Herleen attending to one of the giant valve ageing racks - simply super stuff indeed.

After passing the knock test, valves were passed to the main test bench and plugged into a test board where a specially designed  eight position switch  applied successively, appropriate voltages such that values were obtained for the following parameters: - Heater current Cathode current Control grid current Screen current Anode current Total emission Mutual conductance ( at 4 - 7 points on the characteristic curve dependant on valve type) Inter electrode insulation for all electrode combinations Only those valves whose performance fell within specified limits were then passed into "Factory Stock."  In the photograph below we see Enid Barribal testing...

And so the story continues.......... a couple of blog entries ago, we left the production process at the sealing stage at which point we had a sealed and functioning valve, however, further processing was required before it was suitable for use for it was required to undergo a process called ageing. Ageing consisted of operating the valve under load under carefully controlled conditions.  Large numbers of valves were plugged into a socket rack like the one in the photo below: - Once the rack was fully loaded, the valve heaters were activated at a 20% higher than nominal rating, so...