Phase Inverter Bias Voltage

That resistor sets the current of the LTP - in this case, 140v/25.5K is 5.5mA, or 2.75mA per triode. Decreasing the resistance will increase the current; the 60K plate resistors would need to be adjusted in proportion to maintain the same plate voltage.

In the diagram, the driver is running 130v at 2.75mA; the spec sheet example is 150v at 8.2mA per triode. So there is plenty of room for increasing the driver current.

While there are technical effects, they are small enough that I would expect listening to be a more reliable guide. It's an easy experiment, only three resistors to change. Try it and see!

Grid stoppers too, posted on January 17, 2017 at 14:12:19
Paul Joppa Industry Professional Posts: 7295 Location: Seattle, WA Joined: April 23, 2001	I would use grid stopper resistances on all four grids, since transconductances are 5mA/v or greater.

RE: Phase Inverter Bias Voltage, posted on January 17, 2017 at 15:17:19
sony6060 Audiophile Posts: 1465 Location: USA Joined: August 8, 2014	What would happen if I increase or decrease the -140 volts?

RE: Phase Inverter Bias Voltage, posted on January 18, 2017 at 05:48:12
Michael Samra Dealer Posts: 36118 Location: saginaw michigan Joined: January 30, 2005	If you increase the minus 140v,the cathode voltage will rise and the 5965 will draw less current. I'm not sure why they need a minus 140v to feed a cathode that needs 2v? "For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

RE: Phase Inverter Bias Voltage, posted on January 18, 2017 at 06:35:23
dave slagle Manufacturer Posts: 5430 Location: NYC Joined: April 27, 2001	try grounding the cathodes through a 350 ohm resistor to get the 2V bias and see how the splitter works :-) dave

RE: Phase Inverter Bias Voltage, posted on January 18, 2017 at 07:14:52

PakProtector
Audiophile

Posts: 12360
Joined: May 14, 2002

Use Ohm's law. You can assume the actual bias voltage is a constant, and call it 2 extra volts across the tail resistor. IOW, make the negative rail deeper( more negative voltage) you will have to pass more current. Make it shallower( less negative ) and current through the tail resistor will drop.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

RE: Phase Inverter Bias Voltage, posted on January 18, 2017 at 08:04:10
sony6060 Audiophile Posts: 1465 Location: USA Joined: August 8, 2014	The phase splitter does not have a typical capacitor on the one grid going to ground. It is grounded directly. Due to this does not the negative 140 volts place the tube in a proper balance?

RE: Phase Inverter Bias Voltage, posted on January 18, 2017 at 10:55:54

dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001

Tubes amplify the difference between the grid and the cathode and since the grid is grounded the signal must appear at the cathode in order for that section to amplify. Luckily there is an inverted signal appearing at the other tube sections cathode and in order to keep from attenuating it you need as high an impedance as possible from both cathodes to ground. The sole reason there is a - supply is to make the cathode resistor as large as possible and still be able to pass the plate current. If no negative supply is available some have had good results from using a choke or taken to the extreme a CCS can be used.

dave

Tube DIY Asylum

Phase Inverter Bias Voltage

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