geiger counter

What is the Best Geiger Counter?

Selecting a Geiger counter for your science hobby...

What is the Purpose?

When asking, “What is the best Geiger Counter?”, one must ask oneself, first, what the overall purposes mainly are. Geiger counters are not a one-size-fits-all. Since there are numerous interests or goals to consider before deciding, here, we focus on features to look for more than exact models.

GQ GMC 600cheap geiger countervintage Geiger Counter CDV-700

Vintage or Modern?

Vintage Geiger counters like a old Civil Defense unit definitely win in the Coolness Factor category for a lot of people. A character in “The X-Files” or J.J. Abrams’ “Fringe” is likely to be sporting a sizable unit like a lunchbox with a wand and a needle gauge. This type of unit can be the most fun to use for anyone who likes the charm of older tech, but they can also need updating or repair, and lack modern bells and whistles and more.

Many modern Geiger counters can log and remember data with a timestamp for days on end. Often, they can connect to computers to build graphs or charts based on the data they’ve recorded. Digital displays allow for easy reading and even cycling through modes such as Counts Per Minute (CPM) or dose values such as Rems or Sieverts.

A Note on Reading Rems or Sieverts vs. CPM :

Since Geiger counters may measure counts more accurately than dose equivalents, remember that two perfectly operating, freshly calibrated Geiger counters can easily give you dose readings around 20% different from one another because they were set up using different calibration sources (for one thing). You either have to take dose readings on Geiger counters with a grain of salt or know what isotope your unit was calibrated to (dose-wise) and how similarly that applies to your target check source material for accuracy.

Geiger counters can only read counts, not energy levels. They merely convert CPM to doses by using a static mathematical conversion formula, and this formula is different for different source materials because they each yield counts that are worth differing amounts of energy per count. A Cs137-calibrated unit will be off, dose-wise, when measuring Co60 and vice-versa.

How Sensitive Must it Be? (A Biggie!!)

Different Geiger counters often don’t even display even remotely the same CPM as each other. One of the biggest misnomers is that two properly calibrated Geiger counters will always get the same CPM reading as each other when sharing a check source at the same distance or spot. This is actually quite incorrect (easily by a factor of 5x or even 20x) and leads to puzzled complaints by buyers of geological specimens, to the sellers, wondering why they get a lower or higher reading than advertised. This is because one of them is using a more sensitive probe than the other.

The Nuclear Regulatory Commission also regularly receives reports that someone shipped someone else a package that was emitting well over the legal limit of radiation for the type of container or labels they used. This is because a less sensitive Geiger counter was used at the origin to test the package surface before release, then an unnecessarily sensitive unit or probe was used on the receiving end, freaking out the recipients without cause.

This is mainly because of differing probes being used, and all may be “correct” despite major disparities between levels displayed. Some probes are inherently less sensitive than others, and you can’t simply compensate by making electronic adjustments during calibration. If an end-window probe is 5x less sensitive than a pancake probe, you can’t just crank up the electronics to be 5x more sensitive for the end-window probe, to compensate during calibration, in order to make the unit with the end-window probe yield the same readings as the one with the pancake probe. It doesn’t work that way; to put it scientifically – it would throw everything out of whack (esp. between different isotopes and profiles of radiation). This is further explained below.

Geiger counters can have:

(Internally as wands or internally integrated)

Side window probes

geiger mueller probe

these are the least expensive and also the least sensitive. They often measure beta and gamma (and not alpha). Modern units GQ GMC 300 through GQ GMC 500 have one of these (the 500+ has two) and the typical, vintage, yellow CD-V700 has one by default (you know if it reads from window slotted on the side on the nickle-plated “hot dog” probe). Low-radiation sources (like salt substitute or fertilizer) may not register on this at all, and a uranium glass marble will yield very little reading. Old, active Fiesta Ware ceramic or a thorium lantern mantle should show up just fine. A radium-painted alarm clock will show on these relatively well, even through the clock’s glass. Commercially available rocks (see our affiliate ads to the side!) are read well by these probes unless the specimen is very low-level. Autunite will make it go pleasantly nuts.

End window probes

end window geiger counter probe

these are considerably more sensitive than side-window probes and usually have a thin mica window on the end allowing good alpha particle readings. These are a good compromise between a pancake probe and a side-window probe in price and sensitivity (esp. price). You won’t read a banana as being above background level (which it technically is, due to potassium) but you can get threshold readings from fertilizer etc. and even small, positive hits from occasional, random pieces of granite or quartz that have trace elements with nuclear decay going on. Of course, with it being both more sensitive and also reading alphas, “all the usual suspects” listed above (check source specimens like Fiesta Ware) will make a unit with an end-window probe really sing. It can really be a lot more rewarding than a side-read probe.

Pancake probes

pancake probe for a Geiger Counter

these are the most expensive so far listed, here, and are often about 500% more sensitive than some end-window probes. In fact, if a vintage Geiger counter is fit with a pancake probe like 44-9 and the unit only goes up to 100x scale, a fairly hot collectible rock or an shielded radium clock face may peg the needle, up close. Many units can read a spectacular range of radioactivity with a pancake, though. This kind can be hugely fun, as you can begin to get threshold readings from a banana, a human, get really positive readings from salt substitute or uranium glass, and many random objects. Vintage units like a Ludlum 3 can often be seen sporting a round pancake on the end of its wand, as well as modern Ludlum Geiger counters made in a similar shape. They are also put inside 1-piece units like the GQ’s GMC series’ 600+ model.

Even higher sensitivity — from here the list goes on to more specialized and mainly industrial examples, from alpha probes with far more surface area to, even, scintillator probes that actively amplify weak gamma signals with a photomultiplier tube inside . With a directional scintillator you may detect uranium from across an entire area, helping you play a game of “hotter/colder” when prospecting, but the meter can get pegged with max. input once you get too near the outcrop or source, so you need to shut it off and deploy a lesser sensitive probe unit to look more closely for the rocks.

Further Sensitivity Factors:

Even the three main hobby types, listed above, vary in readings between models (on calibrated, accurate devices) because of:
total probe surface area
tube wall or window thickness
– amount of anode (receiving element) inside

…and other variables.

All Geiger Counter calibration really means, here, is that exact same hardware can be set up to yield exactly the same, expected results. Other than that, the hardware can wildly vary readings from the same sample, and they are, albeit counter-intuitive, all “correct”. New hobbyists can be seen buying a pancake-equipped unit (capable of alpha, beta, and gamma readings) and using it alongside their side-window unit (capable of beta and gamma, only). They often think that if they subtract the side-window’s readings from the pancake’s readings the remainder will be pure alpha, but its just not so. The pancake is also more sensitive to the gamma and beta.

One thought example (surface area, alone):
If I tell you a piece of autunite is yielding 35,000 CPM… is that radiation measured over 2 square cm or 20? In fact, if you want to know how much output the specimen is emitting, would you like to know just from one direction, or 360 degrees around the rock?

For these types of reasons, clinical specs are often cited along with the exact
and isotope and distance from it used for calibration

In Conclusion:

We hope we shed some light on types of Geiger counters or features and facts to consider when selecting a Geiger counter. It is largely based on one’s measurement expectations, budget, and even taste.

The nostalgic author’s go-to unit is currently a Victoreen 493 with an end-window probe. I also have a CD V-700 refurbished with solid state hardware, with the standard side-window probe which I am considering modifying with a x200 scale option and a pancake probe. See our article about selecting a vintage Geiger counter.

vintage geiger counters

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Choosing a Vintage Geiger Counter

Many of us find ourselves in the market for a vintage Geiger counter. Like radios and other gear, they have a pleasing, well-built charm.

vintage Geiger Counter CDV-700

Electro-Neutronics CD V-700 with alpha-sensitive end window probe. Licensed image courtesy of Bullet308

While vintage Geiger counters can be very appealing and economical, we do need to a) keep them running and b) get out of them whatever total functionality we truly require. You may be surprised to find out that even the most basic, old Geiger counter can have its headphones output routed into a modern Windows device to digitally convert and log data! We provide that free software in the links, further down.

Advanced Needs vs. Standard

Two categories emerge in our deciding on the best vintage Geiger counter. We’ll call them Advanced and Standard. We’ll get Advanced out of the way, first, because the majority of this article focuses on the advantages of a particular model well-suited for Standard needs for a number of reasons including community support – the CD V-700 (see Standard, below). More is not necessarily better unless you need it.


If we were looking to hook up, drive, and interpret findings of advanced probes like a gamma scintillation probe (a special, amplified probe that can detect very faint or distant traces, as for longer-range prospecting), then a good Ludlum unit for an acceptable price would be up our alley, such as the Ludlum 3 (most of their models that accept an external probe are full-featured units). Ludlum units are very reliable, seemingly made with above-average components, because we find them working fine, without ever having been refurbished (maybe due for calibration), for decades. They are also equipped with advanced features not required for basic readings for typical, exploratory hobby purposes.

Vintage Geiger Counter

Even with the basic, insensitive beta/gamma-only side-read probe, this Ludlum 3 sold on Ebay for well over $600 by seller “my_brain_fart”

For these reasons, it’s usually difficult to find a Ludlum Geiger counter in reliable shape for less than $350, at best, if not much more ($700 or more is common for a nice one) – and be careful of condition, as probes are particularly easily damaged or contaminated. They’re also more complicated and tightly packed with parts if you’re considering working on one inside.

We’re planning a Ludlum for outdoor prospecting, to use to find outcrops at a distance with a scintillation probe, and then approach with our more standard Lionel CD V-700 or Victoreen 493 after we get closer to the right rocks (at which point a scintillator would be overloaded with excess signal). There are other good brands like Bicron, Johnson, and others (even fancy desk units called scalers) but that’s for another article. The Ludlum 3 or similar gets our Advanced vote for Vintage Geiger Counters and is on our 2022 wish list. It’s so popular they still make a similar version of it.

→ Standard ←

The CD V-700 !

When we’re looking to buy a (another) great-looking vintage Geiger counter, we’re looking to save money, and we are using a standard Geiger–Müller probe (possibly even relatively sensitive ones) then our hands-down winner is the CD V-700!

CDV-700 Geiger Counter


Our refurbished Lionel CD V-700 (left) is very similar to our stock Victoreen 493 (right). We may put the end-window probe on the V-700, recalibrate it, and refurb the Victoreen later.

The CDV-700:
Were produced (and still exist) in countless number
Can be found very inexpensively
Are easy to repair, as they are simple and spacious inside
Can be modified and upgraded in numerous, well-documented ways
Have considerable technical information available for them
Have plenty of compatible parts and even prefab assemblies available
Are a real piece of world history, connected to Civil Defense

Numerous versions of the CDV-700 were made by a number of companies for Civil Defense issue. Usually colored yellow and emblazoned with the cool, Civil Defense “CD” logo, they were made by the thousand by companies including Lionel, Anton, Electro-Neutronics, and Victoreen.

CDV-700 Vintage Geiger Counter

They are similar in general design to the Ludlum 3 discussed., but would require an inordinate amount of work to adapt to scintillation probes or to accomodate advanced adjustments and functions.

The CDV-700 does employ a standard 900v power supply which will run many, typical probes, anywhere from the stock, side-read, gamma/beta “hot dog” probe, to a thin mica end-window probe, to a pancake probe (each example increasing progressively in sensitivity from first to last). Geiger counters require re-calibration if not other minor adaptations if upgraded in this fashion, but it is a straightforward process.

CD V-700 Resources

There are too many makes of the CDV-700 (some with minor internal differences) to to feature them all the manuals here by exact name, but you will have no problems finding the standard literature for yours doing a simple search. The main thing is to seek out not only the primary users manual (usually called “Instruction and Maintenance Manual”) but also, if available, the Shop Manual. This can be more difficult to find but contains more information. The Shop Manual for the Lionel CD V-700 Geiger counter, at least, is below (along with numerous users manuals). Also, it is the authors’ understanding that the Lionel and Anton units are particularly similar.


GeoElectronics CD V-700 Stuff

George Dowell of GeoElectronics is, among other things, a pioneer of refurbishing the CDV-700 (with solid state hardware) as well as modifications and upgrades.

Here he shows how to take an Electro-Neutronics Inc. CDV-700 (dubbed the “ENi”) and use its preferred layout to host the preferred components from the Lionel unit, merging the best of both models into what he calls the “LENi”. He also does various other things like adding a speaker and a built-in pancake probe. You don’t have to intend on doing all of this to get a lot of extra understanding of the CDV-700 Geiger counters with this fabulous article that has been hosted on multiple amateur radio forums:

KFF Homebrew Tips: Geiger Counters in the Ham Shack (at


KFF Homebrew Tips: Geiger Counters in the Ham Shack (at eHam, with comments)

The only sub-link that doesn’t work lately for us is his “Speak2Me” CDV-705 Clone audio module instructions in PDF format, but here is a working HTML copy of that:

Speak2Me CDV-705 Clone Audio Module Instructions

audio module for cd v-700


GeoElectronics offers key parts for the repair, refurbishing, or modification of your CD V-700. You can find two accounts on Ebay, both valid.

The main one seems to be simply:


and the other to try is:


CD V-700... Software?!

One of the advantages of modern (but sometimes joylessly plastic) radiation meters is that they can log data and save the record digitally. Believe it or not, you can do this with the CD V-700 or any other Geiger counter that sends clicks out of an audio jack, using Windows freeware called CDV Counter! We just tested it in Windows 10 and it runs fine!

CDV Counter Freeware for Windows:
SourceForge Download Link for CDV Counter

SciHobby Direct Download:

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Geiger Check Website

In Closing...

While a Ludlum is on our own wish list for prospecting with a 3-inch-wide gamma scintillation probe (there are some great scintillation probe refurbs and DIY kits on Ebay) we love turning people on to the community support, resources and possibilities still available for the CD V-700 which one may find seriously lacking for many other vintage Geiger counters.