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The Blackburn site was making CRT cathodes for the Philips organisation when the diversification into valve making began. Hence the use of CRT type cathodes in the design. The demise of the television picture tube ended the dream and Philips closed the factory.
The following is taken from the Effectrode site.
After almost 30 years the Blackburn site was manufacturing tubes again - 100% British made tubes! The TechTube Blackburn E813CC was a serious engineering effort to redesign the ECC83 dual-triode from the ground up with an improved specification. First impressions are that the glass envelope of this new tube is not as elegantly shaped or as aesthetically pleasing as the old Mullard tubes however what's of real interest is what's inside. On closer examination it can be seen that the internal construction is completely different from a typical ECC83. Instead of concentric electrodes where the heater is at the centre and surrounded by the cathode, grid and anode like the layers of an onion, the E813CC has a much simpler planar electrode structure. Undoubtedly this was simpler to fabricate, reducing the requirement for manual assembly. Microtech were not using the old Mullard ECC83 tooling, but were leveraging their existing cathode-ray tube manufacturing capability to create an audio tube with an utterly unique cathode construction. These guys were the genuine article, real engineers with a passion for what they were doing. They really did know their stuff, a few of them had served apprenticeships in the Mullard workshops and there are still references to the patents they hold relating to improvements in cathode materials for valves.
Close-up of the E813CC electrode assembly. Photograph taken by Neville Roberts in 2009
Technically there were several electronic performance advantages to the planar construction and new cathode. Firstly, the cathode heater drew only a third of the current that a typical tube does - from the data sheet 122 mA verses 300 mA. This meant the tube ran cooler and because of this would have lent itself not only to use in amps but more compact tube gear such as effects pedals and on-board guitar preamps. Secondly, the inter-electrode capacitance was much lower than a normal ECC83 because of the lower surface area of the planar metalwork. The grid to cathode capacitance was specified at 0.4 pF (25% of that of a traditional valve) and a grid to anode value of 0.9 pF (50% of that of a standard valve).
The E813CC was initially announced in September 2008 but wasn't released on to the market until July 2009. The engineers wanted to ensure this tube was the absolute best they could achieve and had been involving guitarists and hi-fi enthusiasts in audio listening tests along the way to get feedback on its tone quality. It's my understanding that some of the audio listening tests had deemed the tube to be excessively microphonic (sensitivity to picking up and amplifying external vibration) which is an issue with all tubes to a greater or lesser extent, old and new. And putting a tube in a high gain application such as a guitar preamplifier section is effectively like putting it under a powerful microscope - look hard enough for flaws like microphony and you will find them. The small dimensions of the electrodes might not have helped the situation either as they would surely ring at a higher resonant frequency yielding a noticeable different microphonic signature to a traditional tube. Something else out of the ordinary to pick up on.
But the design team stoically took on board these criticisms and undertook further research in an attempt to engineer out the microphony. Their published conclusion was that it was possible to reduce the microphonic pickup however the tube did not sound subjectively as good. Now there is something in this. If a tube is capable of picking up a little ambient vibration or sound in a controlled manner, it will add more depth, body and sustain. However this not in the mainstream thinking and certainly something the MicroTech team could have perhaps done without being 'bogged down' with at this stage. They had been keeping potential customers informed of technical difficulties every step of the way and I canbt help but think that their honesty and commendable efforts to show willing might have in some way damaged customer confidence. They were even shipping tube dampers with tubes - which aren't guaranteed to be an effective solution - it doesn't inspire confidence.
Sadly the glory of this new and innovative tube was terribly short-lived - Blackburn MicroTech Solutions went into administration in September 2009 - just a few months after they'd started shipping out their first new valves.
Reference: Effectrode.
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