A place where old GM counters are restored.

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Richard Hull
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A place where old GM counters are restored.

Post by Richard Hull »

My first pass at restoration of an old portable GM counter of the "U Boom"

I will let this post be a running report on my efforts to restore ancient (1940's-1960's) GM counters. The official U.S. Uranium Boom ran approximately from 1949-1960. The government stopped buying from lone wolf mines and miners and contract bought from only mining companies as the glut of Uranium due to the Boom proved to be far more than anticipated to make the atom bombs for defense and as starters for H bombs. There was even a surplus for planned future nuclear power plants. The lone prospector was "aced out", and the last great mineral rush in U.S. history was at an end.

To start off, we will look at my work in bringing a Technical Associates F-6 portable GM counter up to modern usage and operation.
I assumed it worked perfectly when I bought it about a year ago.

Generalities associated with typical U Boom portable, vacuum tube GM counters one might encounter

All portable GM counters of the time period mentioned above, that were of significance, used vacuum tubes. Transistors would creep into GM counters in the very late 50's but the cost of a counter did not drop as transistors of the type required were still not cheap. Transistors would not really be a true replacement for vacuum tubes in GM counters until the mid 1960's, long after the U Boom had pretty much ended.

The average "good" counter of the peak early 50s period was priced at $100-$300 1950's, "U boom" dollars. The very best GM counters might run up to $500.

I looked up the price of a a 1951 Ford or Chevy and you could buy one brand new for $1,300. So a GM counter was a significant chunk of one's income and not purchased on a whim. The federal mandated minimum wage in 1953 was 75 cents/hour, and went up to $1.00/hour in 1956. Again, any nuclear instrument in the middle of the "U Boom" was a big investment.

Most GM counters of the period used large B batteries to power up the plate circuits of the vacuum tubes. These were invariably 45 volt or 67.5 volt batteries. Two of these in series would power the plate circuits with voltages of 90 and 135 volts respectively.
These batteries were made by many manufacturers, (Eveready, Burgess, Ray-o-Vac, Star, etc.). All companies made and sold these batteries into the 1970's or beyond. Only Eveready manufactured them into this century. Eveready changed hands two or three times and stopped manufacture of all "pile" batteries in 2011. All such batteries were of the carbon-zinc chemistry type.

It is important to all future operation of such GM counters that some scheme be devised to use modern batteries which are readily available to keep these relics alive. This means we must construct a small, compact, high frequency power board to generate the needed 90-135 volts DC at a few milliamps. (0.5 watt capacity) Fortunately a large fraction of the volume of those old counters was devoted to the B batteries. This means a lot of space for modern batteries and the small circuit board to generate the power supplied by the old bulky B batteries.

Such circuits rely on a key, small transformer of the iron core or ferrite core design. Most will use the venerable 555 IC with a few other components to do this job. The circuit is abysmally simple to construct. The transformer is the key!! You will have to cast about for a miniature transformer, usually found in a well stocked electronic junk bin. It will have a low ohm primary, (1-5 ohms), and a high ohm secondary, (1k-10k ohms). Note, these are only tentative DC measured resistances.

I will let this replacement supply and its design go for this first post. I will give more details in a future reply post here to elaborate to this subject in more detail.

For now, I just submit images of this counter mentioned above. All images are self-explanatory and labeled with text. Suffice it to say, the counter still worked great. It just needed a B battery solution seen in the images.

Of note here is the philosophy of U hunting at the prospector level with a GM counter.

I felt the 0-500 cpm range on this counter was a joke! Any specimen reading so low is driveway stone! However a read in the U.S. Government's free little U Boom period booklet on prospecting for Uranium warns of "over burden" and "backgrounding". Over burden was when you were in a hole or had rock hanging over you as in a rock cliff shelf. Your background might go through the roof and look like a strike on a mother load. Likewise, if you had true hot rock that you just picked up and have to change ranges to read it, you might want to leave the counter on the 0-500 cpm range and walk away from your hot wall of rock until the background dropped to half scale or so and then read your rock on the high scale and subtract the background reading if it proved a significant fraction of your high scale reading.

There are many other ways to be fooled with a GM counter in a desert filled with possible U finds. You are even warned in the little prospector's guide of A-bomb test fallout in the area making everything on occasion seem hot. Yes, Virginia, they were setting A-bombs off like firecrackers every year in the southwest at the height of the U Boom!

Feel free to comment on any of my postings in this thread as it will grow as I work old GM counters back to life.

Click the images to enlarge and read. Then click the back arrow (top left) to return to images

Richard Hull
Attachments
Tech Assoc F-6 mod.jpg
Tech Assoc meter mod.jpg
Tech Assoc bottom board.jpg
Tech Assoc guts upper board.jpg
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: A place where old GM counters are restored.

Post by Richard Hull »

Batteries - semantics - and types.

Old GM counters used only two types of batteries an "A" battery or batteries to power what was always 1 volt filament vacuum tubes. (1U5, 1R5, 1S4, etc.) A compliment of 3 to 5 tubes were the norm. The current demand on these batteries was a constant 100ma to 200ma. Thus the most common "cell", (semantics), was a "D" cell. In some cases two or more were hooked in parallel for more current capacity, and thus, longer life. In most all cases, the A battery requirement is easily handled today as D cells are still common in both carbon-zinc and alkaline chemistries. The "A" battery issue is solved.

The other type of battery is the B battery. These supplied plate voltages of 100 volts or more directly from a "pile" of small 1.5 volt cells stacked one on top of another. This is a type "battery" as it is composed of many cells, thus, a "pile" battery (semantics again). Only two batteries were commonly used in all GM counters during the U Boom and afterwards. These were the 45 volt battery, 30, 1.5 volt cells and the 67.5 volt battery, 45, 1.5 volt cells. I show images of these historic and not longer available carbon zinc batteries, below.

The individual cells in these batteries were about 1-inch square and about 3/16" thick with flat plates on each for contact in series piles. They were pressed together is suitable stacks and heavily waxed without any soldered of other wire connection between them. The stacks were wired together and then encased in a sturdy carboard casing with "button, press contact terminals" on top of the battery. These small cells could reliably put out up to 50 ma under heavy load, but were more normally called on for only a few ma in any instrument we are talking about in the nuclear arena.

As such, B batteries tended to last a very long time, often beyond even a reasonable shelf life, provided intermittent use in on-off mineral sampling periods. Even under heavy use, they would spring back to full voltage after a 24-48 hour period of disuse due to the carbon-zinc technology de-polarizing compounds included in their chemistry. Eveready had the cat jumping through the "9" signifying their motto "bounces right back after use" having 9 lives, like a cat.

What batteries can I use to power my high frequency 120 volt replacement circuit?

It is to be remembered that the plate circuits in most GM counters only needed a few ma from their B batteries. This would mean your little power board might source 120v at 3-4 ma. That is .36 to .5 watts of power to the GM circuitry. As no such leap to higher voltage occurs without a power lose in the circuitry, this might mean .5 watts to .75 watts of input power might be demanded from your modern battery choice.

Let us say you choose to use two 18650 LIPO re-chargeable cells in series for a total of 7.2 volts, nominal. That means the current drain from these might demand as much as 100ma. As these cells are normally 2000mAh or more, 20 full hours of run time might be available between charges. Considering intermittent use, this might mean months on a charge.

Alkaline batteries would demand 5 minimum, 1.5 volt alkaline cells to deliver the 100 ma current drain. Do you have room for 5 alkalines in series?

NiMH is a great choice due to their AA cell power density, but they internally self discharge far more rapidly than LIPO batteries do.
These would be fine for a week long heavy usage period, but would not be of much use in 6 months without a recharge cycle.

This covers what the first sentence of this reply stated and makes you smarter than the average bear on old GM battery history and what you might consider in the way of modern batteries to power you B+ eliminator board during restoration.

Battery addendum: We are discussing only GM counters here, but ion chambers of old and new still typically need 100 volts to bias the chamber. As the max load on this voltage in a transistorized or IC based ion chamber is on the order of 1-5 micro amps, most ion chambers used 4 slender 22.5 volt batteries to do this work. I bought an older, but modern transistorized ion chamber that uses 3 D cells and 4 of the 22.5 volt slender batteries back around 2004. The 22.5 volt batteries that I bought back then still read their full summed 90 volts today and are working great. Shelf life and beyond! When they die I will have to make up a board to get this voltage.

Richard Hull
Attachments
The great Eveready logo of many years.  Touting the fact that it bounces back after use.
The great Eveready logo of many years. Touting the fact that it bounces back after use.
The 45 volt battery in its last packaging.  No cat!
The 45 volt battery in its last packaging. No cat!
45 volt batt.jpg (7.82 KiB) Viewed 3297 times
Battery packaging from 1990 up to 2011 for the 67.5 volt battery....The cat is gone!!
Battery packaging from 1990 up to 2011 for the 67.5 volt battery....The cat is gone!!
Battery packing of the 67.5 volt circa 1960s
Battery packing of the 67.5 volt circa 1960s
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: A place where old GM counters are restored.

Post by Richard Hull »

Basic B battery eliminator circuit - example

The image and little circuit below always works for me. My motto is keep it simple and use components at hand and components that will be available forever. (more or less).

I have already discussed modern battery considerations above which might be used to power this circuit. I typically opt for two LIPO cells in series which can range over their useful charge voltage of 8 volts to 7.2 volts at the typical current to this little circuit of 70-100ma.

The important thing, as noted earlier, is your choice of transformer that functions in the circuit to give 130 volts to a load that will demand 2-3 ma minimum. this means that under test, you will need to hang a 47 k ohm load resistor on the output of your little board during design and testing to make sure you have 130 volts output to this load.

Transformer choice

I have noted above the transformer can be miniature, or should be. It must have a very low ohm winding on one side and a very high ohm relative winding on the other side. The low ohm side is the one that hooks to the driver transistor out of the 555 IC. The high ohm side goes to the high voltage diode output circuit.

I am using a tiny iron core speaker output transformer from a number of surplus houses. These are typically out of old transistor handheld radios of the 50's -90's. 3-8 ohms on one side and 1k-5k ohms on the other side. I have also used a far more common ferrite core miniature transformer only found on the fluorescent tube driver boards off dead big screen TVs! One of these boards could easily contain 8 identical little transformers that are perfect for a high frequency B battery eliminator circuit board. Typical primary secondary readings are 1-2 ohms or less and from 700-4k ohms on the HV side.

Iron cores in, miniature, usually drive at 5-20khz, while ferrite cores run 20khz or more. I will add an image below in future of typical examples of small transformers that work for me across the broad range of such circuits.

You should know that with various transformers, you may have to adjust the circuit component values a bit. Remember what works is what works.

A good test setup is this small circuit, seen below, wired up on a "proto board". Feed this circuit from your chosen batteries, but have a 0- 200 milliamp meter in series with the battery's positive input to your test circuit. Put your test transformer in the circuit, place the frequency adjust pot at midrange. turn on the power and watch your input current! A good transformer will work at 100 ma drain or less from your battery! Do not let the 200 ma meter peg by adjusting the frequency pot to some current drain of 100 ma or less. Only now look at your output voltage. Is it in the range of 80-180 volts? If so, tune the frequency around to make it 130 volts with the 47K ohm load. Again watch that battery current! If no where in the pots range do you get any where near even 50 volts out, you might try another transformer. But, before moving on to another transformer, try reversing the primary leads! It typically will make a difference in output voltage!!!

Richard Hull
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Transformers.anno.jpg
GM battery eliminator. anno.jpg
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: A place where old GM counters are restored.

Post by Richard Hull »

Typical proto-boarding

Attached are images of my proto-board efforts to match the simple 555 circuit to a ferrite transformer. I have 20 of these little guys and it makes sense to work up a circuit for them as I have several old GM counters that need the 125 volt B battery supply.

Proto-boarding means you need a proto-board strip or a phalanx of them, as I do. A good supply or your actual battery to be used along with two meters minimum. In addition, you will need appropriate IC chips various resistors and capacitors related to the above diagram in the previous postings here.

The images are pretty self-explainitory with more than enough text to get the overall idea of this effort.

Richard Hull
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Protoboarding (1).JPG
Protoboarding (2).JPG
Protoboarding (4).JPG
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: A place where old GM counters are restored.

Post by Richard Hester »

I have a number of old, busted Victoreen 440RF survey meters that I bought on spec. Some of them have punctures in the Mg foil shielding the ionization chamber. Does anyone know of a source for replacement foil? I could probably replace the Mg foil with aluminized mylar, but then I'd have to re-calibrate...
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Re: A place where old GM counters are restored.

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How odd... I, this morning, contacted Dave Hamric of Metallium and he has rolled a piece of Dysprosium foil for me and it is on its way here.
Dave noted that he can roll foil of almost any element from his massive store of pure elements.
I have sold Dave a lot of my elemental materials obtained years ago.

I once had to refuse 500 lbs. of free .999 magnesium scrap. (wire, sheet, rods, plates. All were either cutoff scrap odd small lots of unsold magnesium, etc.) It was either take it all or leave it. The metals place would not be credited on returned Mg at that time. The mill would take all the scrap you sent by way of gift, but you had to pay freight.

Visit Dave's sales site, and see his elemental coins, his "marketplace" and his special items he has made to order over time.
He will and can do special finish work on his elements.

https://www.elementsales.com/index.html

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: A place where old GM counters are restored.

Post by Richard Hester »

A source states that the Mg foil window on the 440RF is 13 mg/cm^2. From the density of Mg (1.738 gm/cm^3), this works out to 0.007 cm thick.
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Re: A place where old GM counters are restored.

Post by Bob Callis »

Excellent information Richard. Looking forward to more. Thanks!
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Re: A place where old GM counters are restored.

Post by Jon Rosenstiel »

1955 Pop-Tronics article.
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Re: A place where old GM counters are restored.

Post by Richard Hull »

Jon, Thanks for the PDF on this issue of Popular electronics. GM tubes back then were on the order of $5 each for some of Raytheon's classic hyper thin walled glass tubes. As with any counter, the tube was the high dollar item. Better tubes like the Victoreen 1B85 were about $20.00.

I actually have two or three "pumpers"! Like the putt-putt boat fusion, the "pumper GM counter" was hyper cheap and required continuous human input to work! Most all were under $20.00 and housed in thin, cheap molded plastic cases.

The hard part of a really good Geiger counter after the GM detector tube was the associated circuitry and the cost of vacuum tubes and the expensive B batteries needed to generate the 600-1000 volts to run the GM tube.

The pumper had a $5 GM tube, a surplus audio transformer, one resistor and one .05 1kv disc capacitor plus a single push button. You had to supply headphones and one or two 8 cent D cells. The pumper had no on-off switch! You pressed the button by pumping on it constantly when you wanted to use the counter. This button pumping connected the transformer's 8 ohm winding to the 3v "D" cells. The pulsing created HV spikes from the high impedance secondary going to the capacitor which, after a suitable number of tedious pumpings, would charge the capacitor to the high voltage needed by the GM tube which would send its pulse to what was usually a 100,000 ohm crystal ear plug headphone to create the clicks indicating radioactivity. On the best units this clicking might last 20 seconds on background, but a real hot sample would stop counting as the charge would quickly drain out of the capacitor in under a second!!. So, for hot specimens you had to continuously pump that #@%$*!! pushbutton.

If you had $30.00 you could have the push button replaced by a tiny vibrator also powered by the same 3 volt D cells. $40 would add a headphone, neon bulb flasher and a real metal case housing the counter with an over the shoulder leatherette strap. While all of these low priced counters worked, I call them "kludge" counters. Cheap, troublesome and of little real value qualitatively or quantitatively. The little vibrator needed constant cleaning and adjustment of the contacts. With a real on-off switch, the long run times afforded by the vibrator, really drained the D cells, often in less than 1 hour run time. But 8 cents would get you a pep boys tar top D-cell and 12 cents would get you a top of the line Eveready D cell.

In short, you needed to plan on $100 minimum for a decent useful counter and if serious prospecting was intended, close to $200 would be needed.
At the time of publication of this magazine, the U.S. minimum wage was 75 cents per hour. A full three 40 hour week's wages at minimum wage would be needed, after taxes, to buy a $100 counter and it came with no batteries. Add $5 for batteries.

Speaking of batteries....I just discovered Eveready made a "W5" battery that put out a whopping 1245 volts!! can you imagine the interior insulation on that bad boy. I had though their top voltage was the 535 volt xenon strobe photo flash battery. Nuclear Chicago made a BF3 neutron counter that used two of these W5 batteries to get the 2200 volts needed to the BF3 detector tube.

I attach an image of a Nuclear Chicago vibrator cheap GM. This was the best you could buy from a reputable company but was still $49.00 1955 dollars.

Richard Hull
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Typical cheap GM counter.  Nuclear Chicago "Super Sniffer".  A vibrator unit 2 D cells $49.00 in 1955
Typical cheap GM counter. Nuclear Chicago "Super Sniffer". A vibrator unit 2 D cells $49.00 in 1955
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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