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Single Ended Triodes (SETs), the ultimate tube lovers dream.

RE: Determining the size of inter-stage coupling cap

A little more,

the "AC impedance" (known as reactance) of the choke falls with frequency. A 1000Hy choke has a reactance of 6.3 meg ohms at 1000Hz but only 125k ohms at 20Hz.

The other issue is this, when you have a cap feeding a choke you have a 'tank circuit' and that LC tank circuit will have a low frequency resonance.

Depending on the DC resistance of the choke, to keep the resonance frequency below the audio band (and low in amplitude) it takes a rather large coupling cap (3uf to 10uf just as a ballpark number).

The BCP-16 GC has 3850 ohms of resistance and that's not enough to allow a "normal" sized coupling cap (.1uf to 1uf just as a ballpark number).

When the coupling cap is too small you can get an audible increase in the level of the low frequencies. Some use this to "tune" a system.

Have Fun and Enjoy the Music
"Still Working the Problem"

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