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 300b polarity
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 28th July 2012, 10:01 PM #1 diyAudio Member   Join Date: Oct 2009 300b polarity anyone knows how to polarize a 300B, with all measurements and calculations on all adjust the resistance of the cathode. I have the outline that I send.the output transformer is 3K
 29th July 2012, 05:39 AM #2 diyAudio Member     Join Date: May 2005 Location: USA Blog Entries: 7 Not 100% sure what you're asking here. The voltages for any VT are always measured relative to the cathode potential. Since the grid of the 300B is very close to DC ground, and the cathode is at 69Vdc relative to ground: Vgk= 0 - 69= -69Vdc This would be your grid bias. Makes no difference if the cathode is at ground potential while the grid is actually -69V WRT ground (a fixed bias circuit). either way Vgk= -69Vdc This schemo shows the plate at 425Vdc WRT ground. Since the cathode is at 69V, then: Vpk= 425 - 69= 356Vdc That comes pretty close to suggested SE operating conditions from the spec sheet. __________________ There are no foxes in atheistholes www.dolphin-hsl.com
 29th July 2012, 03:00 PM #3 diyAudio Member   Join Date: Oct 2009 300B thanks, I want to know the characteristics of the valve as I regulate the resistance of 880 ohms to get the job miliamperioscde. where I put the milliammeter in which points of the circuit to work in point (class A) the valves I have are Gold Lion PX300B. The output transformer 3K based on the schema that I have sent and finally, the filaments esan 5V DC adjustable resistance function have.Un greeting.
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Join Date: Jan 2008
Location: Eureka, CA
Quote:
 Originally Posted by miguelnoda thanks, I want to know the characteristics of the valve as I regulate the resistance of 880 ohms to get the job miliamperioscde. where I put the milliammeter in which points of the circuit to work in point (class A) the valves I have are Gold Lion PX300B. The output transformer 3K based on the schema that I have sent and finally, the filaments esan 5V DC adjustable resistance function have.Un greeting.
Hi,

Instead of polarize or polarity we use the word "bias". It sounds like you want to calculate the operating conditions for your 300B,

The milliamperes current can be found by measuring the voltage across the 880 ohm resistor and using Ohm's law I = V/R (current = voltage / resistance).

If you measure 69 volts across 880 ohms you have .078 amperes current or 78 milliamperes.

If you have 78 milliamperes current in the 300B and 356 volts across it, you can use Watt's formula (P = I x V) to determine that you have 28 watts plate dissipation.

If you want to change this by changing the value of the resistor, you will need to learn about plate curves and how to construct a load line.

 30th July 2012, 07:27 PM #5 diyAudio Member   Join Date: Oct 2009 300B thanks for replying first. If the characteristics of the set 300b and 53ma-5.1ma / v would have to adjust 880ohm resistor to work is my question. This is inscribed on the box.
 31st July 2012, 04:26 AM #6 diyAudio Moderator     Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6 Should not need to adjust anything for it to work, not that critical - a couple of mA one way or the other is not going to significantly affect performance. If your B+ is significantly higher than predicted you may want to adjust the resistance value upward slightly to compensate. (Just add small series resistor - does not need very high power rating as it will be dissipating a small % of the overall power.) __________________ "To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
 31st July 2012, 10:03 PM #7 diyAudio Member   Join Date: Oct 2009 300B thank you all. The strength that I have is 880 ohm adjustable and if I could adjust You have to drop the resistance I insert the milliammeter of resistance ground to fine adjust? Another issue is that capacitors are good for power, I have a 47uf-600v solen of the input and filter after the shock of two Mundorf of 47 +47 and the other is the step that I have I have two Dynamicap. a greeting

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