50s Prospectors geiger counter? - Page 1
Forum section: electronics / repair

author: nelsonm
author_rank: Contributor
timestamp: July 31, 2017, 07:53:04 am
content: So I took this neat little thing apart today, I'm curious as to what I'm missing, I strongly feel that the battery connector I was poking at may not have been the regular 9V that I assumed, and there's another pair of wires with two little stubby pokey bits at the end that I just don't understand. Any ideas on where to start my searches would be appreciated. I'd like to hear a crackle at least from this thing some day :-)https://www.youtube.com/embed/tcO-hSdJtWs**EditIt looks like the company "Sharpe Instruments Ltd." has evolved to "Scintrex Ltd." today (Obvioiusly I'm still searching aafter posting this)

author: chris_leyson
author_rank: Super Contributor
timestamp: July 31, 2017, 08:21:28 am
content: The battery connector with the two round pins is most likely for a 90V battery and the two press on connectors would be connected to a low voltage battery for the heaters, most likely 1.5V. Look up the data sheets for the tubes and they will tell you what the heater voltage is.

author: nelsonm
author_rank: Contributor
timestamp: July 31, 2017, 09:00:03 am
content: So I can find the datasheet for the big tube in the middle of the box. It's a CK1027 Cold Cathode Half-Wave Rectifier->Design center maximum ratings:Peak Inverse V: 2800VMaximum Anode Supply V (peak): 1700VMinimum Anode and Starter Electrode Supply V: 750VThese number seem... high... or there must be some sort of voltage amplification going on.The other tubes are about an inch and a bit tall and are marked RCA 4-45 Made in USAI can't seem to find anything on them.There's one more piece of glass without any markings at all on it. It looks kind of like a neon tube with a small white cylinder or plastic material of some sort in it.

author: chris_leyson
author_rank: Super Contributor
timestamp: July 31, 2017, 10:27:22 am
content: Hi Nelson, I'm guessing the thing that looks like a relay is going to be a vibrator supply, don't know what voltage it would run off maybe 6V or 9V, just a wild guess, wouldn't think it runs from 1.5V but I could be wrong. Looks like there are two small transformers, the one in the center next to the CK1027 is probably a step up transformer for the Geiger tube and the one by the speaker would be the audio output transformer. Couldn't find any data on the RCA 4-45. Miniature wire ended tubes from that era would have heater voltages either 1.25V or sometimes 0.625V so you would wire two heaters in series if running from a 1.5V heater supply.Many if not most of the miniature wire ended tubes do not have a cathode and would use one end of the filiament. If the tubes have 4 wires they are most likely triodes and the connections would be F-, F+, G and A, where F+ would most likely serve as the cathode, that way the grid would be biased to -0.75V (average heater voltage) assuming 1.5V heater supply. Pentodes would have five wire connections, F-, F+, G1, G2 and A, where G1 is the control grid, G2 is the screen grid and G3 the suppressor grid would be internally connected to either -F or even sometimes +F. Given time I think you will have to trace out all of the wiring to figure out what is going on.EDIT: I should add that maybe the HT battery could be 45V or 69V and not 90VChris

author: gadget73
author_rank: Regular Contributor
timestamp: August 01, 2017, 12:20:06 am
content: Looks like the GM tube (the silver thing on the bottom) is smashed. You can probably sub one pretty easily, though the calibration will be off since the response characteristics are not likely identical to yours.Probably only really sensitive for gamma radiation, but it may do beta as well if the window on the tube is exposed. It wouldn't make a great prospector's meter honestly. Uranium is primarily an alpha emitter. Alpha is very hard to detect, a sheet of paper will block it. In the soil you may as well forget it.

author: nelsonm
author_rank: Contributor
timestamp: August 01, 2017, 04:46:50 am
content: Yeah, grandpa was more a trapper than a prospector, so I don't know how much research he would have done before buying a tool like that. He mostly did gold panning to kill time between walking his trapline I think.This coming weekend I'm going to get out the pen and paper (or fritzing) to try and cobble together a schematic of sorts.I also emailed the company on the off chance that someone had hoarded their old marketing materials or manuals, but no luck... it was a long shot but never hurts to ask