Re: For Kurt or ? input tube bias?

Posted by Kurt Strain on March 27, 2001 at 19:12:12

In Reply to: Re: For Kurt or ? input tube bias? posted by SteveBrown on March 27, 2001 at 18:19:34:

> > And why doesn't an input of 3v (rms) cause a tube biased at -2 volts to clip, since that represents more than 8v p-p? What am I missing here? < <

Okay, I think I understand this, but it's not a good situation. You are seemingly operating this driver stage class A2 with a strong low output impedance generator. You have a fairly remote cutoff for the tube, meaning even at (-2V-4V)=-6V you are not cut off fully. On the other swing you are at (-2V+4V)=+2V which is pulling positive grid current, which is class A2. Add a 100K series resistor in between the generator and the input grid and see if it still as clean on the output of this driver. I bet not. If it did, it would be class A1, otherwise you are requiring strong grid drive from the preamp and operating it class A2. Not the normal mode of operation.

You should be able to design this driver biased and loaded such that the driver tube will send the output into clipping before entering class A2 operation. I would work on that. For a 300B with -60V Vgk you need to swing +/-60V peak without needing the driver to go into positive grid current. You have to set the bias and load lines properly, and it should be able to do it even if you have only a Vgk of -2V on this 6N1P, but it might be very close. You need a minimum gain of 30 which requires a high load resistor or choke load or CCS load.

> > Also, as I look at other drivers, what does it mean when the top clips before the bottom? < <

You reached cutoff of the tube (very negative grid voltage) before you reached max turn-on of the tube (positive grid voltage).

> > Or vice versa?> >

Vice versa. :-)

Kurt

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Follow Ups Full Thread

Topic - For Kurt or ? input tube bias? - SteveBrown 11:30:17 03/27/01 (14)

Re: For Kurt or ? input tube bias? - SteveBrown 18:19:34 03/27/01 (10)

Re: For Kurt or ? input tube bias? - Sacreficialanode 08:12:53 03/28/01 (0)

Re: For Kurt or ? input tube bias? - Kurt Strain 03/27/0119:12:12 03/27/01 (8)

Re: For Kurt or ? input tube bias? - stevebrown 19:18:43 03/27/01 (7)

Re: For Kurt or ? input tube bias? - Paul Joppa 23:13:47 03/28/01 (3)

Re: For Kurt or ? input tube bias? - SteveBrown 11:13:43 03/29/01 (2)

Re: For Kurt or ? input tube bias? - Roscoe Primrose 13:46:24 03/29/01 (1)

Re: For Kurt or ? input tube bias? - SteveBrown 15:17:50 03/29/01 (0)

Re: For Kurt or ? input tube bias? - Kurt Strain 21:30:18 03/27/01 (1)

Re: For Kurt or ? input tube bias? - Kurt Strain 21:32:09 03/27/01 (0)

With two stages (nt) - Roscoe Primrose 20:56:35 03/27/01 (0)

Re: For Kurt or ? input tube bias? - Kurt Strain 14:16:01 03/27/01 (2)

Re: For Kurt or ? input tube bias? - dave slagle 16:33:30 03/27/01 (1)

That's true. Good point. nt - Kurt Strain 19:14:53 03/27/01 (0)

Follow Ups

Re: For Kurt or ? input tube bias? - Kurt Strain 03/27/0119:12:12 03/27/01 (8)

Re: For Kurt or ? input tube bias? - stevebrown 19:18:43 03/27/01 (7)

Re: For Kurt or ? input tube bias? - Paul Joppa 23:13:47 03/28/01 (3)

Re: For Kurt or ? input tube bias? - SteveBrown 11:13:43 03/29/01 (2)

Re: For Kurt or ? input tube bias? - Roscoe Primrose 13:46:24 03/29/01 (1)

Re: For Kurt or ? input tube bias? - SteveBrown 15:17:50 03/29/01 (0)

Re: For Kurt or ? input tube bias? - Kurt Strain 21:30:18 03/27/01 (1)

Re: For Kurt or ? input tube bias? - Kurt Strain 21:32:09 03/27/01 (0)

With two stages (nt) - Roscoe Primrose 20:56:35 03/27/01 (0)

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