MORNING STAR OBSERVATORY
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RCA WF-12A Geiger Counter

This RCA geiger counter is a prospecting and survey instrument from the 1950's and provides three indicators for detecting radiation; a meter that reads counts per minute (CPM), a flashing neon lamp on the front panel, and audio output to a set of headphones.

​When calibrated the meter's sensitivity is 2000 CPM = 1 mR/Hr. The meter scale is 0 - 100, and the instrument has three ranges, X1, X10 and X100. On X1 a full scale reading of 100 CPM = 0.05mR/Hr.

Picture
The counter is in decent condition, no rust to speak of and only a minor scratch or two, and there is a bit of a crack in the clear face of the meter. As found, it did not work and needed some troubleshooting. The "toilet lid" cap on the 1/4" phone jack was also broken so I removed it. It's useful in that it keeps dirt and moisture out of the counter, but it also makes it a pain to get the headphone plug in and out, so I don't really miss it. But if I can repair the cap I'll probably reinstall it.

Picture
Inside the unit is clean, for once no dead, leaky batteries to deal with. Battery-wise, it uses three 1.5V "D" cells to power the filaments of the three 1U5 tubes, and two 67.5V "B" batteries that provide the 135VDC B+ for the tubes.

The biggest downside to restoring equipment like this is the "B" batteries, it's just not cost effective to buy the batteries anymore. They cost more than the instrument itself. So in this counter I'm doing away with them.

Picture
I only needed to replace a few parts to get the counter working again. To start I replaced the old 500uF electrolytic capacitor in the meter circuit, and the selenium high voltage rectifier, which was open. It was replaced with a 3000PIV silicon diode. Also several out of tolerance resistors were replaced.

​One issue I had working on this counter was the placement of the inductor leads for the high voltage oscillator. If the leads are not kept clear of the circuitry as much as possible it will cause the counter to run away clicking, and can quickly peg the meter and possibly even damage it.

Picture
The 1B85 geiger tube is housed in an aluminum probe.

Picture
This is the DC-DC boost converter I'm using to replace those expensive 67.5V "B" batteries. I'm setting it up to convert 12VDC to 135VDC for the B+. The model number is YH11068A and can take a 10 to 32VDC input and boost it to +/- 45 to 390VDC. (There is also a version with the same model number that only has a single +45 to 390v output). The higher the output voltage the higher the duty cycle and current draw from the batteries.

To replace these batteries I ​adjusted the module for +/- 67.5V to the module common (marked as GND), and since it's providing a positve and negative output, the negative out is actually used as the ground to the counter. This provides +135VDC with the caveat that the module's common is not used and is kept isolated from the metal chassis so as not to short out the negative output.

Picture
The DC converter mounted in the battery compartment. There's still plenty of room for a 12V 2000 mAh Ni-MH "AA" battery pack. All that's left to decide is how I want to go about recharging the pack.
So far the counter is working very well with this high voltage boost module. I'm running the module from a power supply while testing, but as soon as the battery pack arrives in the mail I'll check the run time on batteries. I'm already sure there won't be any more expensive "B" batteries needed for this geiger counter.

Picture
This is the 12V 2000mAh NiMH battery pack. I have been using it for several days testing the counter and it's hardly dropped the battery voltage at all. The power supply's ammeter I was using for testing shows the module draws ~40ma, so I can already see the battery is going to last a good while on a single charge.

Picture
Picture
A cardboard sleeve was added around the battery so it wouldn't knock about in the compartment, and it's connected using Anderson power pole connectors. The section of the range switch that powered the 135V "B" battery on and off was rewired to switch the 12V battery instead.

Picture
This is the 12V NiMH charger for the battery pack. All together the boost converter, battery pack and charger cost about $45, less than the price of just one expendable "B" battery.

Picture
The meter is working well and is just counting background radiation in this photo.

Page created 4/22/2021
​Last update 4/30/2021
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  • Home
    • About
    • Contact
  • Astrophotography
  • The Observatory
    • The New Observatory
    • - About the ExploraDome
    • - About the Lancaster Dome
    • - Building the Lancaster Dome
  • Equipment
    • CCD Cameras >
      • Orion Starshoot Pro
      • QSI 683WS
      • ZWO ASI-178MM
    • Eyepieces
    • Filters
    • Mounts >
      • Orion HDX-110 (EQ-8) >
        • New HDX-110 Setup
        • Orion HDX110 EQ-8
    • Observatory Computers
    • Telescopes >
      • Astro-Tech AT6RC
      • Celestron C-11 XLT
      • Zhumell 152mm Refractor
  • Projects
    • Arduino Focuser
    • C11 XLT Mods
    • Orion SSPRO Camera >
      • Disassembled Views
      • Noise Reduction Mod
      • Temp Controller Mod
    • Ultima 8 Mods
    • Zhumell Refractor Mods
  • Non-Astronomy
    • Amateur Radio >
      • Boat Anchor Radios >
        • BC-348N Receiver
        • Collins 51J4 HF Receiver
        • R-392 HF Receiver
      • DIY >
        • Station Boom Microphone
      • Ameco >
        • Ameco AC-1
        • Ameco OCM
        • Ameco PT-2
        • Ameco R5A
      • Heathkit >
        • Heathkit SB-102 Station
      • Knight-Kit >
        • Knight Kit Span Master II
      • Yaesu FT-817 >
        • Yaesu FT-817ND
        • LDG Z-817 Autotuner
        • Windcamp LiPo Battery
    • Antique Radios >
      • Building A Radio Workbench
      • Radio Dial Neon Clock
      • Radios >
        • 1938 Zenith 6-S-254
        • Echophone EC-1
        • Eltz Radione 2
        • Panasonic RF-5000A
        • Silvertone Model 4465
    • Geiger Counters >
      • AN/PDR-27G Radiac Set
      • Lionel CD V-700 Geiger Counter
      • RCA WF-12A Geiger Counter
    • Test Equipment >
      • DIY Test Equipment >
        • DIY Curve Tracer
        • DIY Signature Tracer
      • Military Test Equipment >
        • BC-221-AF Frequency Meter
        • LM-21 Frequency Meter
        • TS-323/UR Frequency Meter
        • TS-465 C/U Sweep Generator
        • TS-505D/U VTVM
        • TV-3C/U Tube Tester
      • Tube Testers >
        • Alternating Current Sink
        • Drug Store Tester
        • EMC Model 200 Tube Tester
        • Hickok Model 6000A Tube Tester
        • Hickok OZ-1 (550X)
        • Precise Model 111 Tube Tester
        • Precision Model 10-12
        • Supreme Model 385
        • TV-3C/U Tube Tester
      • VTVMs and Multimeters >
        • B&K Model 290 Hi-Low FET Multimeter
        • Hickok 225K VTVM
        • McMurdo Silver VOMAX 900
        • Micronta 22-220 FET Multimeter
        • Simpson 360-2 Digital FET DMM
        • TS-505D/U VTVM
      • Hickok >
        • Hickok 19X RF Generator
        • Hickok 225K VTVM
        • Hickok 288X RF Generator
        • Hickok OZ-1 (550X)
        • Hickok 6000A Tube Tester
      • Simpson >
        • Simpson 360 DMM
        • Simpson 360-2 DMM
        • Simpson 480 Genescope
      • Supreme Instruments >
        • Supreme 385 Automatic
        • Supreme 560 Vedolyzer
        • Supreme 560A Vedolyzer
        • Supreme Model 561 AF/RF Generator
        • Supreme's Model 562 Audolyzer
        • Supreme Model 562 Audolyzer circa 1941
        • Supreme Model 562 Audolyzer circa 1946
        • Supreme Model 563 Audio Generator
        • Supreme Model 576 RF Generator
      • Other Test Equipment >
        • Heathkit IT-28 Capacitor Tester
        • Rider 162 Chanalyst
        • Tektronix 326 O'scope
        • VU-Data Model 941B Oscilloscope
    • ---------------
    • Fossils
    • Rocks and Minerals
    • Star Trek >
      • Star Trek Rock Mood Lamp
      • Star Trek Communicator