hi, i was wondering if its possible to bypass a 874 tube in a power supply. if so how could it be done?? thank you.

You could use a resistor ..but it will run way way hot..This tube breaks down line volatge by roughly 20 volts.... I have some of these if you need them...

:hi, i was wondering if its possible to bypass a 874 tube in a power supply. if so how could it be done?? thank you.
:

:You could use a resistor ..but it will run way way hot..This tube breaks down line volatge by roughly 20 volts.... I have some of these if you need them...
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::hi, i was wondering if its possible to bypass a 874 tube in a power supply. if so how could it be done?? thank you.
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hi. this tube is used in a rca, duo rectron model-AP-937. i have 450 volts at the plate. a good 80 tube in place of the 213 tube. the chokes are good. the caps are good. the 874 tube does nothing except make a complete circut for ac. i was told this tube should glow purple when working. i have no way to test this tube. thank you.

:hi. this tube is used in a rca, duo rectron model-AP-937. i have 450 volts at the plate. a good 80 tube in place of the 213 tube. the chokes are good. the caps are good. the 874 tube does nothing except make a complete circut for ac. i was told this tube should glow purple when working. i have no way to test this tube. thank you.
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I am not familiar with this particular tube, but all regulator tubes i know of glow purple. Actually, they are not vacuum tubes at all, but argon tubes.
Lewis

::hi. this tube is used in a rca, duo rectron model-AP-937. i have 450 volts at the plate. a good 80 tube in place of the 213 tube. the chokes are good. the caps are good. the 874 tube does nothing except make a complete circut for ac. i was told this tube should glow purple when working. i have no way to test this tube. thank you.
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:I am not familiar with this particular tube, but all regulator tubes i know of glow purple. Actually, they are not vacuum tubes at all, but argon tubes.
:Lewis
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Lewis

If the tube is glowing (and not arcing), and the voltage at that point is about what it should be, then the tube is likely fine. If you put the power supply on a Variac, you should be able to vary the input voltage quite a bit without the voltage at the regulated point varying much. I believe the range is about 10 volts, but varies for different regulator tubes, and a tube manual should be consulted for certainty. The regulator tube will not, of course, maintain proper voltage at that point when the power supply either puts out less voltage than is needed or more voltage than the regulator can handle. The regulator tube is a shunt type regulating device, and merely wastes the excess power.

...Also, there are some regulator tubes that glow orange (neon), and there may be others that use other gasses, but I don't know of them. Ionization of the gas is perportionate to the voltage fed to the tube, to a degree, and so the tube will draw more current when fed more voltage, thus absorbing the excess (the resistor that feeds the circuit also absorbs quite a bit of the excess).

T.

:If the tube is glowing (and not arcing), and the voltage at that point is about what it should be, then the tube is likely fine. If you put the power supply on a Variac, you should be able to vary the input voltage quite a bit without the voltage at the regulated point varying much. I believe the range is about 10 volts, but varies for different regulator tubes, and a tube manual should be consulted for certainty. The regulator tube will not, of course, maintain proper voltage at that point when the power supply either puts out less voltage than is needed or more voltage than the regulator can handle. The regulator tube is a shunt type regulating device, and merely wastes the excess power.
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:...Also, there are some regulator tubes that glow orange (neon), and there may be others that use other gasses, but I don't know of them. Ionization of the gas is perportionate to the voltage fed to the tube, to a degree, and so the tube will draw more current when fed more voltage, thus absorbing the excess (the resistor that feeds the circuit also absorbs quite a bit of the excess).
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:T.
the 874 tube does not glow. just completes the ac, circut. unable to get any dc volts at the terminals. thank you

Unfortunately RCA used conventional battery type triode designations for the pins of this tube in the schematic for your power supply (AP-937), so it is a bit confusing at first. However, regarding that, this tube has no grid or plate or filament. There is a jumper between pins + and P. This jumper, as you already know, completes the AC circuit. That way, should the tube be removed, the entire power supply is shut down, for if it wasn't, the voltage that this tube controls would run away. Pins - and G connect to the actual internals of the tube--the part that should glow. You should get 90 volts across these pins. If you get more, and the tube isn't glowing, then the tube is likely bad. If you get less, like 0, then either the tube is shorted internally, or the resistor that feeds this portion of the circuit is open. Check the divider resistor for full continuity at every point.

Assuming that the schematic is a bottom view of the tube socket, hold the tube with the two big pins upward. Then go about measuring continuity according to the schematic. You should have full continuity across pins + and P, but not pins - and G. All other indications of tube functionality will be given by what I just described above.

T.

I misused the word full when referring to continuity. For the resistor, I meant that there should be continuity across the resistor and at every tap in between, but, of course, there should be resistance to that continuity.

Regarding the jumper in the tube itself, it should read 0 ohms.

T.

I misused the word full when referring to continuity. For the resistor, I meant that there should be continuity across the resistor and at every tap in between, but, of course, there should be resistance to that continuity.

Regarding the jumper in the tube itself, it should read 0 ohms.

If the resistor is open at the 90 volt point, consider that the tube may have arced over internally, especially if the resistor is burned. If there is corrosion or a mere break, then the tube may be okay.

T.

:I misused the word full when referring to continuity. For the resistor, I meant that there should be continuity across the resistor and at every tap in between, but, of course, there should be resistance to that continuity.
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:Regarding the jumper in the tube itself, it should read 0 ohms.
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:If the resistor is open at the 90 volt point, consider that the tube may have arced over internally, especially if the resistor is burned. If there is corrosion or a mere break, then the tube may be okay.
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:T.
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:hi. thank you for the infomation. i did check the resistor. it is not open at any point. i did check the pins on the 874 tube. i got 0 continuity. forgot to say that i do have 190 volts dc at the 135 volt dc terminal.

Check continuity between the high end of the resistor and the 135 volt terminal. If the 135 volt terminal has voltage, and the resistor has continuity at all points, there should be no reason, other than a broken wire or bad connection, why the resistor would not have voltage on it.

T.

:Check continuity between the high end of the resistor and the 135 volt terminal. If the 135 volt terminal has voltage, and the resistor has continuity at all points, there should be no reason, other than a broken wire or bad connection, why the resistor would not have voltage on it.
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:T.
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:hi. i just had a old friend of mine check the 874 tube on his tester. it turns out that this tube i have is a dud. he let me use a 874 tube he has in stock. the power supply came to life with all the proper voltages. now ill hunt for the tube i need. thank you.

Interesting. Did you say that the pins going to the tube internals had 0 ohms or infinite ohms? I am guessing that the tube was shorted internally, and that would be caused by a meltdown, which sometimes happens with these tubes. Glad you got it working, though.

T.