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Old 6th Jan 2019, 4:44 pm   #33
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,060
Default Re: Puzzling audio circuitry

It's pointless to argue whether the 'puzzling audio circuit' is a cascode or not, until you define 'cascode.'

But, the cascode in my book, is the name someone gave to a circuit consisting of a common-cathode stage feeding directly into a common-grid (or earthed-grid) stage. And googling seems to confirm that.

That being so, the 'puzzling audio circuit' is no way a cascode, because although the lower valve is definitely common-cathode, the upper one is no way common-grid. In fact, it's earthed anode, because the anode is at the same AC potential as the input to the stage - in fact, at the same AC potential as the input-return and the output-return.

Agree with Dave RW, the 'puzzling audio circuit' has Miller effect in abundance- and the input will look highly capacitive! Whereas a true cascode, the input looks much less - Cgk + (2 x Cak).

Last edited by kalee20; 6th Jan 2019 at 4:48 pm. Reason: Last sentence added
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