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Author Topic: OA2 regulator  (Read 5461 times)
N4NYY
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« on: April 25, 2012, 06:33:13 PM »

I have one from a friend that he needed testing, so I tested in the "AC5UP approved Heathkit TC-2'. The needle was shimmering/vibrating. The tube measured 15%. The data said a good tube measured 10%, which confused me.

Is this normal or bad?
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AC5UP
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« Reply #1 on: April 25, 2012, 07:00:15 PM »

Beats the purple haze outta' me, but it looks like your friend is as independent of the thought process as you are on this one..............

The venerable 0A2 is a gas discharge voltage regulator / voltage reference tube. Maximum unregulated voltage input is 185 VDC, nominal voltage across the tube is 150 VDC. It has been my experience they rarely go bad and are remarkably close to rated spec. If a person were to hang their Extech across the 0A2 while it was in circuit, what should the reading be? If a person were to measure the regulated B+ (same difference as across the tube, look at the schizmatic) and found it was significantly LESS than 150 VDC, what would that indicate?

Fact is, you don't need a tube tester for this one.

If the regulated line is significantly less than 150 VDC that means too much load (partial short in a condenser?) or the resistor in series with the 0A2 has gone too high. Often the regulated B+ line feeds the RF / IF sections of a receiver and temporarily removing those tubes can create a near no-load test condition. If the voltage across the tube is well above spec that would likely indicate the tube is no longer conducting well enough to maintain regulation and needs replacement.

If this was an equivalent circuit using solid state parts, how would you test the Zener diode?             D'oh!

I give this question Three Vinnies.
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N4NYY
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« Reply #2 on: April 25, 2012, 07:15:02 PM »

Quote
Beats the purple haze outta' me, but it looks like your friend is as independent of the thought process as you are on this one..............

The venerable 0A2 is a gas discharge voltage regulator / voltage reference tube. Maximum unregulated voltage input is 185 VDC, nominal voltage across the tube is 150 VDC. It has been my experience they rarely go bad and are remarkably close to rated spec. If a person were to hang their Extech across the 0A2 while it was in circuit, what should the reading be? If a person were to measure the regulated B+ (same difference as across the tube, look at the schizmatic) and found it was significantly LESS than 150 VDC, what would that indicate?

Fact is, you don't need a tube tester for this one.

If the regulated line is significantly less than 150 VDC that means too much load (partial short in a condenser?) or the resistor in series with the 0A2 has gone too high. Often the regulated B+ line feeds the RF / IF sections of a receiver and temporarily removing those tubes can create a near no-load test condition. If the voltage across the tube is well above spec that would likely indicate the tube is no longer conducting well enough to maintain regulation and needs replacement.

If this was an equivalent circuit using solid state parts, how would you test the Zener diode?             D'oh!

I give this question Three Vinnies.


I do not have the rig. Just the tube. He mailed it (and some others) to me for testing.
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G3RZP
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« Reply #3 on: April 26, 2012, 03:05:07 AM »

My experience has been that if it glows, it's OK. I did read somewhere that some mil 0A2 (0A2WA?) had some radio active material in them to ensure striking, especially in the dark, but I don't know how true this is.

Feed it from about 300 volts DC through a 5Kohm resistor and measure the volts across it.
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KE3WD
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« Reply #4 on: April 26, 2012, 06:24:43 AM »

If he mailed you the tube, be aware that it may have to sit in the upright position for a day or two before being fired up...
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G3RZP
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« Reply #5 on: April 26, 2012, 06:28:27 AM »

WD,

That's cruel!
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N4NYY
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« Reply #6 on: April 26, 2012, 07:43:11 AM »

My experience has been that if it glows, it's OK. I did read somewhere that some mil 0A2 (0A2WA?) had some radio active material in them to ensure striking, especially in the dark, but I don't know how true this is.

Feed it from about 300 volts DC through a 5Kohm resistor and measure the volts across it.

I had a spare that looked new in box and mailed it to him. I had no idea I had it until a few days ago. I do not have the rig of a 300V power supply. Biggest DC supply that I have is your run-of-the-mill 13.8V. I did not have the rig or a comparable one to test. All I had was the tube tester.
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KD0REQ
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« Reply #7 on: April 26, 2012, 09:22:59 AM »

best rundown of radioactive tubes I've fallen across

http://www.tubecollector.org/documents/radioactive.htm

someplace I came across a MIL document, I think for a frequency standard, which listed the three makers of a 7-pin VR tube used in that machine.  the nucleides used by the three tube makers were krypton, radium, and DU (U-238.)  it was noted the tubes were not identified with the 3-blade rosette design.
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N3QE
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« Reply #8 on: April 26, 2012, 09:58:28 AM »

I have one from a friend that he needed testing, so I tested in the "AC5UP approved Heathkit TC-2'. The needle was shimmering/vibrating. The tube measured 15%. The data said a good tube measured 10%, which confused me.

Is this normal or bad?

If a VR tube lights up in the application circuit, it's good.

Note that if the tube doesn't light up that doesn't mean it's bad... it may be that something is wrong elsewhere in the radio. Low B+ is very likely but there's also a series dropping resistor to check, and the VR tube's regulated load may just be drawing too much current or shorted out. In this case the VR tube not lighting up is like the canary in a coal mine, a valuable diagnostic instrument. You'd be surprised how many different failure modes in e.g. a Heath HW-100 can be precisely diagnosed by nothing more than just observing the VR tube glow/noglow in receive and in key-down.

The needle was shimmering/vibrating in the tester because VR tubes make good relaxation oscillators if combined with R's and C's in the right way. See e.g. http://en.wikipedia.org/wiki/Relaxation_oscillator
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N4NYY
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« Reply #9 on: April 26, 2012, 10:19:34 AM »

I have one from a friend that he needed testing, so I tested in the "AC5UP approved Heathkit TC-2'. The needle was shimmering/vibrating. The tube measured 15%. The data said a good tube measured 10%, which confused me.

Is this normal or bad?

If a VR tube lights up in the application circuit, it's good.

Note that if the tube doesn't light up that doesn't mean it's bad... it may be that something is wrong elsewhere in the radio. Low B+ is very likely but there's also a series dropping resistor to check, and the VR tube's regulated load may just be drawing too much current or shorted out. In this case the VR tube not lighting up is like the canary in a coal mine, a valuable diagnostic instrument. You'd be surprised how many different failure modes in e.g. a Heath HW-100 can be precisely diagnosed by nothing more than just observing the VR tube glow/noglow in receive and in key-down.

The needle was shimmering/vibrating in the tester because VR tubes make good relaxation oscillators if combined with R's and C's in the right way. See e.g. http://en.wikipedia.org/wiki/Relaxation_oscillator

Great info. Many Thanks. I sent a spare tube to the person and mailed it out on Monday.
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AC5UP
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« Reply #10 on: April 26, 2012, 04:03:47 PM »

best rundown of radioactive tubes I've fallen across

http://www.tubecollector.org/documents/radioactive.htm

Vinnie is grateful there is no Krypton in a 0A2. Even a little bit can ruin his day............................   Roll Eyes
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N3QE
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« Reply #11 on: April 26, 2012, 04:31:05 PM »

best rundown of radioactive tubes I've fallen across

http://www.tubecollector.org/documents/radioactive.htm

Vinnie is grateful there is no Krypton in a 0A2. Even a little bit can ruin his day............................   Roll Eyes

If I get bitten by a radioactive 0A2, does that give me the power to regulate 150V?
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AC5UP
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« Reply #12 on: April 26, 2012, 05:50:00 PM »

...............only one way to find out!
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G3RZP
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« Reply #13 on: April 27, 2012, 02:34:44 AM »

N3QE

depends on how the kryptonite crumbles!

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K4FMX
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« Reply #14 on: April 27, 2012, 11:43:42 AM »


[/quote]

If a VR tube lights up in the application circuit, it's good.

[/quote]

Not necessarily! I had a VR tube that i accidentally shorted the dropping restor out momentarily. The tube still lit up and seemed to have the correct voltage on it but it did not regulate as expected. With a varying load the voltage would move around about 10 or 15 volts as I remember. After I replaced it with a new tube the voltage was rock solid.

73
Gary  K4FMX
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