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Old 9th Jul 2020, 12:43 pm   #21
Radio Wrangler
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Quote:
Originally Posted by AdrianH View Post
I am trying to picture how it could oscillate
There are plenty of explanations around if you look up "Relaxation Oscillator"

It does indeed use hysteresis and an R-C time constant.

They are not terribly good voltage regulators, but are an awful lot better than unregulated supplies open to mains variations as well as load changes.

As has been pointed out, manu types had traces of radioactive material included to seed ionisation and give lower and more stable striking voltages, but much of thhis material will have decayed by now, affecting characteristics

Little neon bulbs can also be used as voltage references for low current use.

Babani published an entire small book on trick circuits for neon bulbs... many of them relaxation oscillators.

Squegging is another form of relaxation oscillation where the hysteresis comes from the sratr-up and stop characteristics of an intentional oscillator.

David
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Old 9th Jul 2020, 12:50 pm   #22
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Good point, I may have been misremembering my measurements but I seem to recall Am-241 giving off a small amount of gamma but probably not enough (or at least too infrequent) for this application
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Old 9th Jul 2020, 1:17 pm   #23
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Quote:
Originally Posted by barretter View Post
You could use 2 85A2s in series for 170volts. You'd need to include a high-value resistor from the anode of the top valve to the anode/cathode junction of the two valves to make sure that the lower valve strikes.
Now that puzzles me! If one valve strikes, then in the absence of barretter's resistor, the current it is passing can only flow via the other, so that must strike too.

(I can conceive of a situation where with several in series, none of them strike, if the supply isn't high enough (must equal the sum of all the striking voltages). But once one has struck, then the voltage across it will immediately drop to the maintaining voltage, thereby putting a higher voltage on the remaining few, which are then encouraged to strike... Or so it seems to me).
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Old 9th Jul 2020, 1:20 pm   #24
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

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Originally Posted by Radio Wrangler View Post
Quote:
Originally Posted by AdrianH View Post
I am trying to picture how it could oscillate
There are plenty of explanations around if you look up "Relaxation Oscillator"

Little neon bulbs can also be used as voltage references for low current use.

Babani published an entire small book on trick circuits for neon bulbs... many of them relaxation oscillators.

David
This looks like it should explain everything, 122 page 'General Electric Glow Lamp Manual'

https://w5jgv.com/downloads/General%...%20Edition.pdf

John
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Old 9th Jul 2020, 2:06 pm   #25
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

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Originally Posted by GMB View Post
I just noticed that OA2 uses radioactive cobolt-60 to promote clean striking.

That might be a problem because the half-life is only 5.3 years - so it will be very depleted resulting it less predictable operating (but on the other hand, much safer!)
Well the only radiation tester I have is an arduino shield device that uses a Russion tube so not sure how good it is. It shows the background radiation on my desk as being around 12 to 14 counts per minute.

Anyway the only tubes out of the eight I have that seems to raise the background count is two Brimar OA2 style with a ribbed central column, and the one that works can take the count to around 120 to 150 counts per minute. The faulty of the same style takes the count to around 50 to 60 counts per minute.

Is this a lot? No idea, if I put some 2% Thoriated TIG electrodes near the counter I can get over 110 counts per minute.

Of the other 6 OA2 of which all are all straight sided central tubes, non, as I say seem to increase the count and these include Brimar RCA (some marked for HP) and one marked with a Makers 'E' & 'WH'. of these that make no discernable difference 3 (Brimar, RCA-HP & E) work and three do odd things (RCA and 2x RCA-HP).

The tubes were all placed along side the detector, move the tube away from the detector a few inches and I am back to background levels.

Not something I will be getting upset about.

Adrian
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Old 9th Jul 2020, 2:10 pm   #26
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Thanks John I will save and have a read.
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Old 9th Jul 2020, 2:11 pm   #27
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

You're right not to be worried as long as the valves are intact. The big issue with alpha emitters, and to a lesser extent with betas, is if you manage to ingest any particles of radioactive material, either by swallowing it or breathing it in. This can really only happen if the valve is smashed.

Cheers,

GJ
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Old 9th Jul 2020, 2:19 pm   #28
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

GJ;

I have to be careful when I grind the TIG Electrodes to a point not to inhale the dust, the correct thing now would be to get another non-radioactive style.

I think somewhere, I have some old gas mantle's that could take my counter into the hundreds.

Adrian
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Old 9th Jul 2020, 4:04 pm   #29
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

HI
Back in the day I recall some telemetry equipment that used three
electrode cold cathode devices as logic elements.
They had to have a small fluorescent tube in the box to light them
otherwise they became unreliable.
So the standard phone call to the remote site was "has the small lamp gone off?"
"then leave the cabinet door open and leave the room light on."
Ian
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Old 10th Jul 2020, 7:10 am   #30
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

If i understood/translated note 1 on the second page of this datasheet for the ZZ1040 correctly, it says that if you make use the auxiliary electrode you can shunt the main electrode to ground with as much capacitance as you like without the risk of oscillations.

https://frank.pocnet.net/sheets/128/z/ZZ1040.pdf

Greetings,
Robert
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Old 10th Jul 2020, 7:17 am   #31
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Translations skills for me are very poor is that the same style device as the GR16?

https://frank.pocnet.net/sheets/174/g/GR16.pdf

In which case it is the trigger pin that can be done with a cap and is used for things such as relay triggers etc. Have one somewhere came in a batch of 70 valves from the bay but not utried anything with it.

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Old 10th Jul 2020, 8:27 am   #32
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

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Originally Posted by kalee20 View Post
Now that puzzles me! If one valve strikes, then in the absence of barretter's resistor, the current it is passing can only flow via the other, so that must strike too.

(I can conceive of a situation where with several in series, none of them strike, if the supply isn't high enough (must equal the sum of all the striking voltages). But once one has struck, then the voltage across it will immediately drop to the maintaining voltage, thereby putting a higher voltage on the remaining few, which are then encouraged to strike... Or so it seems to me).
You don'r actually need the sum of the striking voltages.

In theory you need with two voltage reg tubes in series the running voltage of one plus the striking voltage of the other and then of course, plus some more to be the running drop across the series resistor which powers whatever is downstream. The idea is that you have high value resistors to unbalance the voltage distribution across the two tubes. The one you give the lion's share of the voltage to strikes, and now the other tube gets a higher voltage to light it up.

As a simple string of tubes, you would in theory need the sum of the striking voltages, plus some drop in the series resistor (load current) but by getting all artful, you can bring it down.

The drawback is that you need enough current to keep the lit ones lit while the later ones are thinking about lighting.

As a number of half-lives of the radioactive assistance have ticked by, the difference between striking and running voltage will have increased, making these things harder to use. Principally the striking voltage will hav gone up.

It should be possible to make a little solid state shunt regulator to replace these valves if they ever become too rare or too intractable, but I'd miss that glow at the back of my AR88.

David
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Old 10th Jul 2020, 8:46 am   #33
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

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Originally Posted by AdrianH View Post
Translations skills for me are very poor is that the same style device as the GR16?
It is unclear to me if every voltage stabilizer with an auxiliary electrode (or starter) allows shunting the main electrode to ground with as much capacitance as wanted. The datasheet for the GR16 does not seem to give information on this matter.

I recently used two ZZ1040's in series to get 200 V for feeding the screengrids of two EL86's in push-pull. But I did not shunt the main electrode(s) with capacitance because I first wanted to know/hear how it would work without capacitance. Because the amplifier works fine like it is, I will leave it like this.

https://www.vintage-radio.net/forum/...d.php?t=168442

Greetings,
Robert

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Old 10th Jul 2020, 11:13 am   #34
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Quote:
Originally Posted by Robert Gribnau View Post
If i understood/translated note 1 on the second page of this datasheet for the ZZ1040 correctly, it says that if you make use the auxiliary electrode you can shunt the main electrode to ground with as much capacitance as you like without the risk of oscillations.

https://frank.pocnet.net/sheets/128/z/ZZ1040.pdf
It's an interesting point- if the striker electrode acts to maintain current of 1mA or greater (in this relatively high-current device with its B9D base), then there presumably isn't the risk of complete extinguishing of the running glow with the consequent need for the voltage to rise to re-strike value- the condition for relaxation oscillation. I would imagine that this principle applies to devices with this main and auxiliary (striker, helper, ignition etc.) anode construction generally. Inspecting devices with the auxiliary anode reveals it to be a thin rod close to the cathode, thus it presumably creates a point/line of intense field strength, promoting ignition that quickly spreads to the main anode. I've used the 150B3 (a lower-current device with striker electrode) as a reference in series-pass regulator circuits and simpler voltage-followers but took care not to decouple the device itself with a bypass capacitor, decoupling the circuit output instead- it seems that the main anode can be furnished with a bypass capacitor after all if the striker electrode maintains a given minimum current.

Yes, the attractive violet glow through the top grille on the Eddystone 750 here makes a fetching "HT present" pilot light!
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Old 10th Jul 2020, 11:54 am   #35
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

I only just realised that I have this document (and found the link to it): https://frank.pocnet.net/other/Telef...isers_1966.pdf

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Old 10th Jul 2020, 1:40 pm   #36
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Regarding the addition of radioactive materials to assist in ionisation, this was not confined to voltage regulator tubes.
Some older types of fluorescent lamp starters, intended for 110 volt to 127 volt circuits (or for two lamps in series on 220 to 277 volts) were slightly radioactive.
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Old 10th Jul 2020, 6:50 pm   #37
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

So are Gas Discharge Tubes for surge arresting.
Beware that these tend to show reduced striking Voltage after every "thump".

GDTs were fitted on the input side of many SWmode PSUs by that very good company based in Yorkshire. On one railway job they were subjected to a lot of mis-treatment. Eventually the GDTs were firing at the peak of mains Voltage thereby taking out the fuses. Maybe in 100 years they would recover and be OK again!
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Old 10th Jul 2020, 7:44 pm   #38
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

the issue of 'getting enough voltage to strike series-strings of VR-tubes but not using a low-value series-resistor which will overload them on startup" was addressed in the 1960s: here's a narrative by G3VA [from his 'technical topics' series]

[apologies for the horrible image-quality].
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Old 10th Jul 2020, 7:56 pm   #39
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

And here's another circuit from the same series, detailing how to get a glow-tube regulator to 'strike' despite the voltage-drop across its series-resistor (under load) being somewhat low.

In times-past I've done a similar thing but feeding the 'starter' resistor directly from the rectifier-cathodes [yes, it;s got lots of ripple but it always worked!]
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Old 10th Jul 2020, 9:24 pm   #40
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Default Re: Cold cathode voltage stabilizers, OA2 and the like.

Hi!

Can I point the OP in the direction of Practical Wireless, July 1962, to the article, "Neons in The Experimenter's Power Pack", by Martin L Michaelis, from A.R.H./W.R.H?

Mr. Michaelis goes into the theory behind, and the correct usage of, neon regulator tubes in great detail and I strongly recommend any Member always has the data–sheet for any n.o.s. neon or other gas–filled regulator tube on hand, together with Mr. Micheaelis's article before attempting to use them in a new or experimental circuit.

I also strongly recommend a minimum anode current of about 15–20% more than the minimum quoted in the datasheet for the tube, this should be adequate to bring the tube into the "normal glow" region of it's characteristics.

As Member GMB quite correctly states, any radio–active material originally incorporated in the gas–filling at the time the tube was manufactured would, by the natural law of exponential decay, typically would have only 3–5% of the radioactivity present when the material was fresh, assuming the tube was manufactured in the 1960s, therefore there would be much fewer ions available to "prime" the discharge.

Theoretically, the tube manufacturers should have compensated for the natural decay in radioactivity from the primer incorporated with the gas–filling, by providing more radioactive material than theory suggests was needed, but this may not have been possible due to safety regulations associated with handling and storing it.

It's for this reason that certain types of cold–cathode regulator tube were manufactured as "triodes", with an auxiliary priming anode or cathode in the electrode system, that only needs a very small current across the priming gap needed to assist the main gap in the tube to strike.

J.B. Dance's book, "Cold Cathode Tubes", (Illiffe, 1966), free from the Internet Archive, is well worth a study as well!

Chris Williams
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