Baird Atomics

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Richard Hull
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Baird Atomics

Post by Richard Hull »

HELP!

I have just picked up a really nice Baird Atomics model 125 ratemeter/scaler/GM counter - (dekatron type). I need either a service manual or someone to look on the back panel of a real unit and tell me the three vacuum tube numbers open to the world. (tubes were actually hanging out the back of the unit!)

All I have are empty, unmarked sockets!! I know one is the ubiquitous 5U4/5Y3/5R4,etc.,etc. Another 7 pin miniature appears to be an OA2, 0B2 or 0C3 regulator. The toughy is the 9 pin miniature in the third socket. What is it?

I have tried all the surplus manual houses. Almost all said, Baird who?!! One manual dealer was totally familiar with Baird Atomics and had a gang o' manuals, but not for the 125.

I have searched the net, sorta', but have come up with zippo.
Look at this as a mission for the ultimate web ferret.

Dekatrons? If you need to ask, you are a young pup under 40 years old. They were an interesting form of digital vacuum tube readout originated in late WWII and hung on by their eye-teeth kicking and screaming into the early sixties.

Thanks to any who can help.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Baird Atomics

Post by guest »

If I were doing it I would goto the MIT Resource Library.
Inquire there first then goto the directory of the school and ask the Physics dept for any hints. These boys love a challange. You might be able to get a xerox of the manual from the patent archives or the copyright people.
Wow decatrons bring back so many memories.
These things predate even nixie tubes.
To those who wonder, they count the numbers with a glowing dot over the number position. They were fun to watch going round and round as they tallied up a count. I had my first taste in 1963 as a boy of eleven. A geiger as I recall.
My best guess on your nine pin is a 507 or 509 tube.
That is if its a small radius minature socket.
You will find that in the fifties when this monster was hatched there were not many minature tube choices, I would wager if you get a manual for the unit closest in number to your unit you would find the amps for the geiger virtually the same. My guess is it's the audio amp.

Feeling Old
Larry Leins
Physics Teacher
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Re: Baird Atomics

Post by guest »

Actually, that's not a bad idea. We used the old Baird- Atomic dekatron scalers in the student physics labs when I was an undergrad at MIT. We also had creaky old carbon pile rheostats, knife switches and 200VDC out of the wall to control electromagnets. If the techs that used to maintain the equipment haven't retired yet, they may still have data on the old equipment. Much of it has probably been replaced, as it was a danger to life and limb, especially the Zeeman effect experiment. Lots of HVDC out in the open...
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Richard Hull
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Re: Baird Atomics

Post by Richard Hull »

Actually the 9 pin is most likely a dual element tube like a 6JD8 or 6AN8, etc. All of the sockets 9 pins are wired (first clue). There are three bypassed neon NE-2 lamps hooked to various pins. (Used to regulate small current voltages on the pins or to break over to low resitance at over voltages.) I have drawn out the basic circuit around this tube and it is a link to the HV regulator tubes screen grid and HV adjust pot.

Finally there is no audio amp in the 125. it is basically an adjustable hv supply 0-2500 volts - a dekatron readout - a GM tube interface and that is it.

The three BNCs on the back are intrinsically all linked, interestingly, by passive components. The HV BNC allows for external use of the HV. A single 1 meg resistor drops down to the GM probe BNC where an 11 meg resistor goes to the 9pin in question. (this may be an electronic quencher circuit!). From this GM BNC a .001ufd, 3kv disc cap drops down to the third BNC marked signal so that the signal can be taken out to an audio amp or other external device. From this same signal jack , a shielded cable runs directly onto the scaler card.

This is pretty much the stock method in which all GM type gas amplier detector circuits are handled. Nothing weird about any of the circuitry except the way that missing 9 pin links to the GM tube and screen grid of the extant HV regulator tube. The more I think about it the more I think that might be a quencher circuit where the HV is shorted out or, more likely opened up, at each pulse. I'll check that out against the several classic vacuum tube quencher designs so brilliantly explained in Korff's book, in my library, tonight.

Actually, the time between WWII and the early sixties was a no man's land where a good counter might include an electronic quencher. Internally or chemically quenched tubes were more for common use than scientific use where high count rates might be encountered. Unquenched tubes were still common then.

Odd, I am currently working on an FET quencher for one of my new, fully quenched 7311 pancake tubes. A quencher circuit will allow a normal, chemically, quenched tube to count at rates an order of magnitude above its realistically realizable chemically quenched rate of ~100,000 cpm. This million cpm counter is with a simple quencher circuit!! An elaborately designed quencher could exceed a million cpm with ease and by a wide margin. There are many seldom used or acknowledged GM tricks which will extend their useful range. This is mostly due to the takeover of modern PIPS and SB detectors counting alphas today. However, real high alpha count rates ruin or degrade both PIPS and SB detectors rapidly, plus, they require a vacuum to do their best work (alpha spectroscopy).

Large, mica windowed, GM tubes are by far, my favorite all time nuclear detector of choice. Nothing is as sensitve or as easy to impliment as a GM tube. Also, the near 100% efficiency for aplhas is nice.

This has gone a bit afield and I will end this for now.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Richard Hull
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Re: Baird Atomics

Post by Richard Hull »

The FET quencher was a flop.....As it should have been.

It seems in my delight over the 1 ohm RDS(on)rating for the 1200 volt FET, I forgot totally about the ungodly capacitance of these devices (I don't normally work with discrete FETs.) I remembered instantly though the moment that I saw that the turn on time actually exceeded the normal dead time of the tube! (Richard Hester could appreciate my faux pas here.)

Oh well, Maybe I will use a tube, ala Korff, after all or if the specs look good a 1400 volt transistor.

Oh, another interesting thing I noted was that the RDS(off), something rarely looked at, I would suppose, was about 10 megohms. I had it figured for more. The result was that with the 3.9 meg resistor normally placed in the geiger circuit, Voltage divider action between it and the OFF FET lowered the tube voltage by over 100 volts! Lotsa stuff bitin' me in the ass on this little micro project. I look at it as a refresher course in FETs and why they are no good for HV work where small currents flow and microsecond switch times are demanded. Just the worst possible app for the component! I couldn't have figured out a worse task for the device.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Baird Atomics (FET Quencher Circuit)

Post by guest »

How much voltage do you need to remove from the tube before it will quench?. Assume that the tube is running around 900V. Will zooming it down to 600V quench the discharge? I think I have an idea....
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Richard Hull
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Re: Baird Atomics (FET Quencher Circuit)

Post by Richard Hull »

I look forward to your idea, but will now shift this to a labeled thread where the wisdom can be better distributed under a searchable heading. I will also answer your question there. We will continue this in Geiger Counter Basics.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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