Back biasing works great!
But if you do not have any extra B+ voltage, a 2A3 or a 300B with bias at -45V or -60V, then back bias does not solve the problem, it makes it worse.
So, just as I proposed, along comes battery biasing!
Problem solved!
But if you do not have any extra B+ voltage, a 2A3 or a 300B with bias at -45V or -60V, then back bias does not solve the problem, it makes it worse.
So, just as I proposed, along comes battery biasing!
Problem solved!
WFCkeyman,
But first, you have to tell them the approximate current the cathode will draw.
Is your schematic in Post # 1 the exact circuit in question?
If that is correct, then 1.2V/ 500 Ohms = 2.4mA.
Perhaps others on this thread can design a circuit, and draw a schematic for you.
But, consider this:
Replacing a cathode self bias resistor, with a -1.2V supply, does Not work the same. . .
Self Bias (500 Ohms) does auto adjust cathode current.
Fixed -1.2V bias does not do any adjusting of cathode current (it is determined by 1.2V bias, Plate Voltage, and the exact tube that is being biased.
Two tubes of the same tube type may have much different cathode current at -1.2V bias.
But first, you have to tell them the approximate current the cathode will draw.
Is your schematic in Post # 1 the exact circuit in question?
If that is correct, then 1.2V/ 500 Ohms = 2.4mA.
Perhaps others on this thread can design a circuit, and draw a schematic for you.
But, consider this:
Replacing a cathode self bias resistor, with a -1.2V supply, does Not work the same. . .
Self Bias (500 Ohms) does auto adjust cathode current.
Fixed -1.2V bias does not do any adjusting of cathode current (it is determined by 1.2V bias, Plate Voltage, and the exact tube that is being biased.
Two tubes of the same tube type may have much different cathode current at -1.2V bias.
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I leave it to the creative ones on this thread to design a -1.2V bias supply
2X 1N4007 in the cathode lead, forward biased.🙂
Does what is required without pain, suffering & agony!
At one time one could go the their local friendly electronics parts store & buy Stabistors made by Generous Electric & others. Some may still be available.😀
2X 1N4007 in the cathode lead, forward biased.🙂
Does what is required without pain, suffering & agony!
At one time one could go the their local friendly electronics parts store & buy Stabistors made by Generous Electric & others. Some may still be available.😀
Attachments
I agree,
2X 1N4007 in series is as simple as it gets.
Let the tube develop the bias voltage.
The bias voltage will be quite constant from tube to tube.
But if there are 2 channels, then the current of the Left channel tube, may or may not be the same as the current of the Right channel tube.
That sounds like a form of Fixed Bias to me.
A 500 Ohms self bias resistor will have a closer match of cathode current from tube to tube to tube, versus fixed bias.
Tradeoffs, just like always.
Pick your tradeoff version.
2X 1N4007 in series is as simple as it gets.
Let the tube develop the bias voltage.
The bias voltage will be quite constant from tube to tube.
But if there are 2 channels, then the current of the Left channel tube, may or may not be the same as the current of the Right channel tube.
That sounds like a form of Fixed Bias to me.
A 500 Ohms self bias resistor will have a closer match of cathode current from tube to tube to tube, versus fixed bias.
Tradeoffs, just like always.
Pick your tradeoff version.
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