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Old 28th July 2012, 10:01 PM   #1
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Default 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
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Old 29th July 2012, 05:39 AM   #2
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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.
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Old 29th July 2012, 03:00 PM   #3
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Default 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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Old 29th July 2012, 05:55 PM   #4
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Quote:
Originally Posted by miguelnoda View Post
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.
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Old 30th July 2012, 07:27 PM   #5
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Default 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.
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Old 31st July 2012, 04:26 AM   #6
kevinkr is offline kevinkr  United States
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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.)
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Old 31st July 2012, 10:03 PM   #7
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Default 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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