User talk:82.32.50.178

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"This of course is complete nonsense."

Why do you write this ?!

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Please give me a url as a reference for this quotation. If I have written this it is probably because what I am referring to is complete nonsense. Why else would I write that ?

82.32.50.178 (talk) 08:46, 11 November 2012 (UTC) Andrew Smith

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OK I have found the reference:

"...however in the later years of the tube era, constructional techniques were developed that rendered this 'parasitic capacitance' so low that triodes operating in the upper VHF bands became possible. The Mullard EC91 operated at up to 250 MHz. This of course is complete nonsense. The anode-grid capacitiance of the EC91 is quoted in manufacturer's literature as 3.8 pF, which is higher than many other triodes of the era, while many triodes of the 1920s had figures which are strictly comparable, so there was no advance in this area. However, early screen-grid tetrodes of the 1920s, have Cag of only 1 or 2fF, around a thousand times less. 'Modern' pentodes have comparable values of Cag. Triodes were used in VHF amplifiers in 'grounded-grid' configuration, a circuit arrangement which prevents Miller feedback."

As my edit makes clear, this is statement is untrue: "in the later years of the tube era, constructional techniques were developed that rendered this 'parasitic capacitance' so low that triodes operating in the upper VHF bands became possible". The reason why triodes can be used as vhf amplifiers is that they can be used in the grounded-grid configuration where Miller feedback is inoperative. This application of triodes has nothing to do with reduced Cag, which, in fact, was never achieved.