Well, we're going to talk about the ECC81 twin triode today, originally designed for TV applications, yes, that's right - TV!!!! All the other valves we have discussed in this World Series of blog entries had been designed for use at the then used British TV frequency bands of 45 - 70 MHz. However, other countries used carrier frequencies at a much higher range within the 100 - 300MHz region at which a low noise level high grade triode would be needed so enter stage left.... the ECC81.
The ECC81 was great because it was inherently a 'low noise' device, for TV, noise manifests itself as random variable emission giving a 'shot silk' screen effect or alternatively due to electron distribution variance which gives a 'partition veil' type of noise but this is normally seen with pentodes only. The ECC81 as a triode would hence only be susceptible to 'shot silk' noise and even then not much of it at all.
It is strange to think of the ECC81 as a TV RF amplifier or frequency changer due to it's useage in many audio iconic amplifier designs but we cannot change Mullard design historical documents!!
Unfortunately, a photo of a Mullard ECC81 is fairly boring so instead, please enjoy this photo of what is regarded as the best ECC81 variant of all time, GEC's A2900 or in military guise, the CV6091: -