I have a circuit with a power supply source of a little over 650 volts. It has a 100K ohm resistor and 8 zeners totaling 353 volts in series connected to ground. The circuit supplies current to the anode of one tube and the control grid of another. With the tubes out everything seems fine. The voltage across the zeners is 353 volts and the voltage across the resistor is 315 volts which is what I want. But if I put the tubes in it falls apart. The voltage across the zeners drops to 261 volts and the voltage across the resistor shoots up to 387 volts. What is going on? Is it that the resistor is bad and failing under the increased load from the tubes? It checks out when I take it out of circuit.
SOS
WILD1
SOS
WILD1
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The shortest answer is that your resistor is too big. The slightly longer answer is that the voltage drop across the resistor is large enough so that the zener is no longer properly biased. The still longer and big picture answer is that a resistor-zener "regulator" is not suited for main B+ supply IMHO.
Your tube circuit probably pulls more current than your zener regulator can deliver.
650v supply - 350v zener = 300v across 100k resistor.
300v / 100k = 3mA.
If your load demands more than 3mA, the zener falls out of regulation 'cause there's no more current left for the zener...
Your data suggest that you need some 4...5 mA (360v-260v)/100k=approx. 4mA.
So you have to use a lower ohm resistor.
Lets say you want some headroom - 10mA that means R = 300v/0.01A= 30k ohm > make it 33k (4...5 Watt requ'd !)
650v supply - 350v zener = 300v across 100k resistor.
300v / 100k = 3mA.
If your load demands more than 3mA, the zener falls out of regulation 'cause there's no more current left for the zener...
Your data suggest that you need some 4...5 mA (360v-260v)/100k=approx. 4mA.
So you have to use a lower ohm resistor.
Lets say you want some headroom - 10mA that means R = 300v/0.01A= 30k ohm > make it 33k (4...5 Watt requ'd !)
Ohm's Law tells me that even when no valves are present the zener string is only getting 3.15mA, probably barely enough to maintain the zener voltage. Take a bit of current (I assume the valve anode takes some current?) and the voltage will drop.
BTW if you want to guarantee a response in under an hour you had better engage an electronics engineer on a retainer contract and pay him well.
BTW if you want to guarantee a response in under an hour you had better engage an electronics engineer on a retainer contract and pay him well.
Nice one
V=I x R...
Is the value correct to the drawing..if no drawing is it correct to the other side? Unless its common to both?
If you measure the resistance is it correct to the marking?
The value could be changed as long as the max current through the zeners is not exceeded..
Then again if this is a design value it should work unless something is wrong with another part of the circuit..
Regards
M. Gregg
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I don't think the resistor has failed.
Fact is, the tube circuit - whatever it is - pulls more than 3mA, which is what the 100k resistor can deliver w/in the range of the zener.
If the power supply was designed the way it is and if it worked before, then the fault may be in the tube circuit. Could be anything, tube failure, blown capacitor etc etc etc
Fact is, the tube circuit - whatever it is - pulls more than 3mA, which is what the 100k resistor can deliver w/in the range of the zener.
If the power supply was designed the way it is and if it worked before, then the fault may be in the tube circuit. Could be anything, tube failure, blown capacitor etc etc etc
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