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In Reply to: RE: Yes posted by Lenin on August 23, 2016 at 22:32:47
"A interstage has the best controle on the grid of the powertube. "
Why is that?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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When using a interstage you have the possibility to have a rock solid bias because of the low dcr of the interstage. Of course you have to use a capable driver tube and use a stable fixed bias of the power tube otherwise you though away all the goods.....
Dc coupled tubes have drift ( not the best bias) and using capaciters for cathode decoupling is also not a good idea for the best performance.
An interstage can also provide for class 2, drive with grid current, if propper designed.
"...have a rock solid bias because of the low dcr of the interstage. "
I used to think that also but then someone explained that the grid current is not DC per se.
The grid current will start and stop periodically in accordance with the music signal that is causing it.
So now it is the reactance of the winding that comes into play, not the DCR.
A good grid choke (or the secondary winding of a good IT) will have a very high reactance, in many instances higher than the grid resistor that it replaced causing the bias to be less stable under class 2 conditions.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Grid current can only be there for very large signals where the grid of the powertube is driven in a postive grid signal. Then there is a much lower impedance so the driver has to be much more powerfull then normally. A normal circuit can't handle this but a powerfull driver+ interstage can.Remember this grid current is a very special situation where impedance is much different then normally so an interstage is still the best solution for a stable bias.
Edits: 08/25/16 08/25/16 08/25/16
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