My line stage consists of a grounded cathode amp cascaded into a cathode follower.
The tube is ECC99 and the operating point is 150V@18 mA each section.
B+ is 360V, load resistor and CF cathode resistor are 10k.
My measurements showed that the GC section draws 18mA but the CF section draws 16,5 mA.
Why ?
Should I reduce the CF cathode resistor at 9,7K to achieve equal current draw and cathode
to plate voltage ?
Thanks
Mic
The tube is ECC99 and the operating point is 150V@18 mA each section.
B+ is 360V, load resistor and CF cathode resistor are 10k.
My measurements showed that the GC section draws 18mA but the CF section draws 16,5 mA.
Why ?
Should I reduce the CF cathode resistor at 9,7K to achieve equal current draw and cathode
to plate voltage ?
Thanks
Mic
> achieve equal current draw and cathode to plate voltage?
Why? What possible advantage could there be?
Why? What possible advantage could there be?
PRR said:
Perhaps to cancel some distortion by operating both valves (of the same type) at the same operating point? 😕
Hmm, I seem to remember something about this from way back.
Wasn't it something about this on the Audio Genesis website? ( now gone )
Something to do with the power supply and subjective dynamics, I believe.
I may be wrong.
cheers 😉
Wasn't it something about this on the Audio Genesis website? ( now gone )
Something to do with the power supply and subjective dynamics, I believe.
I may be wrong.
cheers 😉
I remember reading something like that in an old issue of the "Tube CAD Journal" also... I think it was the cathode follower issue.slowmotion said:
Best regards,
Mikkel C. Simonsen
Hi mcs
You're right it was in "Tube CAD Journal",October '99, page 3.
http://www.tubecad.com/october99/page3.html
cheers 😉
You're right it was in "Tube CAD Journal",October '99, page 3.
http://www.tubecad.com/october99/page3.html
cheers 😉
Pff... sounds like BS to me...
Besides, a CF doesn't produce distortion so it can't cancel any.
Tim
Besides, a CF doesn't produce distortion so it can't cancel any.
Tim
Tim, the idea was that there is a cancellation at the supply end; at AC, as the inverting amp's current drops, the CF's current increases by a near identical amount. So it's a valid way of optimizing a circuit to use with weedy supplies and inadequate bypassing. Of course, it begs the obvious question...
As I'm not an expert, I would like to know if this non-symmetrical operation between the two sections of the same tube is something to worry about.
Normally, each triode shares the same load resistance and current draw. So, in my case I expect to see each section to draw 18mA.
But no, they don't. As I said before the GC section draws 18mA@153V and the CF draws 16.5mA@158V.
Maybe it is not such a big issue and to my ears it performs quite good.
Thanks for your replies.
Normally, each triode shares the same load resistance and current draw. So, in my case I expect to see each section to draw 18mA.
But no, they don't. As I said before the GC section draws 18mA@153V and the CF draws 16.5mA@158V.
Maybe it is not such a big issue and to my ears it performs quite good.
Thanks for your replies.
SemperFi said:
Ok. So tell me, when's the last time you could measure any distortion produced by a typical CF such as the circuit in question, at line (listening) levels such as 1Vp-p or less?
...Yes, it is technically measurable. But using an instrument capable of resolving 0.001% or less is cheating. 😀
Tim
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