Merlin (le Valvewizard ), décidément très occupé, vient de me répondre heir à mon message du 12 juillet !
Comme je suppose que tout le monde a décroché, j'hésite à faire part de notre échange . Ce qui ne me coûte rien c'est copier/coller. Vu le rythme de nos échanges vous avez largement le temps de traduire ( il s'agit du calcul de la capa de découplage de cathode)
Merlin Blencowe a écrit :
>
> Hello Jean-Pierre,
> sorry it has been so long.
>
> I have two requests. Firstly, your formula finds the necessary cathode bypass capacitor (Ck) to give the -3dB point. BUT, under some circumstances, the difference between maximum and minimum gain of the triode may be LESS than 3dB. How does your formula hold then?
>
> Second, you left a post on the forum, showing how to calculate CK graphically. Could you send me your graphical method + instructions, or send me the hyper link (I cannot find it myself now!).
>
> Yours,
> Merlin
Je lui réponds :
Hello Merlin,
First the formula accounts for that . Look at it again :
Code : Tout sélectionner
1 (µ+1)Rk
f = _________*square root of ( (1 + _____ )² - 2)
2 Pi Rk Ck RA + rak
When (µ+1)Rk
( 1 + ________ )² = 2
RA + rak
then f = 0 that is the -3 dB point is the null frequency. But if
(µ+1)Rk
( 1 + ________ )² is less than 2
RA + rak
then it is impossible to find a value for f because this -3dB point does not exist because we are in the case that you mention that is the difference between maximum gain and minimum gain does not reach 3 dB.
Second : you'll find the graphical method here :
http://tabwyp.free.fr/G5/meth_graph_bypass.html
If you need an explanation about it do not hesitate to ask.
Best regards.
Jean-Pierre
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