Over the course of their operation Sylvania used green on their tube boxes, technical literature, merchandise, such as clock radios, enamel advertising signs and thermometers and even the doors and windows on their factory in Emporium were painted green too. The green livery and their oak leaf logo was almost certainly inspired by the verdant Pennsylvanian countryside—there are over 30 species of oak trees in this part of America (only two oak species in Britain).
On closer inspection there are other cosmetic differences in the blue-print tubes that were produced by the Emporium plant from 1986 onward. For instance, tube plates are grey rather than black and this leads one to question whether other, more critical changes were made to the metallurgy and chemistry of the grid and cathode coatings and if these changes affected tube performance in any way. Effectrode were particularly interested to learn what we can about the tube manufacturing processes employed in the Sylvania/Philips Emporium plant as we utilise their subminiature pencil tubes in our compact effects pedal designs.
But without proper acoustic/vibration test equipment, a disciplined test regime and a decent sample set, ideally hundreds of N.O.S. tubes from different batches from each year, it’s virtually impossible to measure any significant statistical variations in tube quality (utterly impossible if you’re just purchasing one or two of these tubes at time). However, Effectrode have been working with Philips ECG tubes for over ten years. During that time we’ve tested and hand-selected many thousands of subminiature 6021, 6111 and 6112 tubes for low electrical noise and microphony, and we’ve learned that some batches of tubes aren’t quite as good as others. Our tube rejection rates for these types of subjective failures run anywhere between 0% to 50% for a carton of 100 tubes.
For example, whilst testing a box 100 green-print 6111WA tubes (batch dated October 1985) we noted consistently low electrical noise and low microphony. These were what we consider “excellent” tubes and grade them subjectively as an “A”. Their performance was exceptionally consistent too and even the poorest performing tubes within this batch would be considered “good” or, according to our grading system, a “B”. Upon completion of testing the green-print tubes we began testing a batch of blue print tubes (batch dated February 1987). It soon became apparent that the blue-print tubes were generally more microphonic than the green-print tubes and also showed wider variability in microphony. Many ended up being graded as a “C”, that is, having adverse microphony—these are considered as unusable tubes—and far fewer of this batch made the “A” grade.
At this point one might reasonably conclude that Philips blue-print tubes are inferior to the green-print variety. After all, the Emporium plant was the last man standing—blue print tubes were manufactured from 1986 onward—they were the end of the line for tubes made in the U.S.A. Perhaps the machines and tooling required servicing or were wearing out? Or maybe less care was being taken with manual assembly on these last production runs? This seems plausible, that is, until we discovered “poor” batches of green-print tubes and they even occur within the same year as the “good” batches! Doh! I’m sure the reader can appreciate our frustrations at not being able to locate those elusive cartons of near perfect tubes that pass our selection criteria with 0% rejects.
