The '63 is an interesting unit electronically speaking. The low range unit uses a 700V G-M tube, but on some ranges is operated below its Geiger region at 500 or 570V. Naturally it doesn't count at the HV. WHy do this? Because all G-M tubes are subject to "saturation" at high count rates.
What this term means is the tube is literally saturated with radiation coming in so fast, it loses the ability to reset itself between pulses, resulting in a ZERO reading, not good.
In practice this is observed when a user is walking or driving into a radiation filed with a G-M instrument, the readings will increase steadily then suddenly drop to zero! High end civilian meters have an alarm, the CDV-700 does not. In the instructions, the manuals always state that they are for training and in-shelter (low radiation fileds) testing of food and water supplies. We're all hobbyists here on this group (for now anyway).
Military recognized this that's why there's an ion-chamber unit in the '63 too, to cover those high radiation fields. Some other RADIACS, instead of an ion-chamber have a very small high-range GM tube piggy-backed onto the main probe body to handle the issue.
But in the '63 while the low range tube is connected, the higher ranges, way outside it's normal capability are access by reducing the DC voltage below the threshold of detection, then briefly pulsing an additional Voltage over the top of it to take a single measurement, knowing the tube may saturate, the pulse is very brief and turns itself off quickly, giving the G-M tube time to reset itself for the next pulse. In this way the G-M tube's upper limit of detection is greatly increased. But this is at a cost, since only a fraction of the radiation strikes are actually being reported.
Some civilian detection units operate with a similar system continuously, therefore their CPM are different from other units using the same tube.
Keep these facts in mind when seeing something being reported strictly in CPM.
Also ALWAYS, always, suspect ANY reports given in mR/Hr units form any instrument, unless all the other measuring parameters are listed as well. Many factors are responsible for correct mR/Hr readings.
Geo
From: "STEPHEN CARLILE via groups.io" <smcarlile@...>
To: "CDV700CLUB" <
[email protected]>
Cc: "tanner carlile" <
tanner.carlile@...>
Sent: Wednesday, April 20, 2022 6:14:56 AM
Subject: Re: [CDV700CLUB] Need Help Modifying the Low Range Probe from AN/PDR-63
Excellent! Thanks,
------ Original Message ------
From: "Geo Dowell" <GEOelectronics@...>
To: "CDV700CLUB" <[email protected]>
Sent: Wednesday, 20 Apr, 22 At 12:10
Subject: Re: [CDV700CLUB] Need Help Modifying the Low Range Probe from AN/PDR-63
That's what I thought.
When you or your son gets a chance, verify the tube # inside there.
That is a great unit to adapt directly to the CDV-700, but is needs a HV adaptor, because the Geiger-Muller tube in it is a typical US military 700V tube.
So conversion is to strip out all that is not associated with the long G-M tube and it's support, install the HV adaptor pcb in the probe body, convert to coax connector on the base of the probe. and it's ready for use on the CDV-700. Nothing need be done to the CDV-700.
Alternatively a single HV adaptor mounted in a slender inline housing box could serve any number of 700V probes.
Those end window probes are sensitive and rugged, as are all the RADIAC series housings, to be sure.
Good project, thanks for posting it.
Geo
From: "STEPHEN CARLILE via groups.io" <smcarlile@...>
To: "CDV700CLUB" <
[email protected]>
Sent: Wednesday, April 20, 2022 5:45:43 AM
Subject: Re: [CDV700CLUB] Need Help Modifying the Low Range Probe from AN/PDR-63
------ Original Message ------
From: "STEPHEN CARLILE via groups.io" <smcarlile@...>
To: [email protected]
Sent: Wednesday, 20 Apr, 22 At 11:23
Subject: Re: [CDV700CLUB] Need Help Modifying the Low Range Probe from AN/PDR-63
George,
Thanks very much. I have looked everywhere for this manual..
The probe is the Low Range Unit, DT-507/PDR-63 as described on page 5-11 and shown in figure 5-5 page 5-19.
It goes thru a box with resistors to calibrate the pulses / voltage...as shown on pages 5-11, 5-12, and 5-13.
Thanks,
Steve
------ Original Message ------
From: "Geo Dowell" <GEOelectronics@...>
To: "CDV700CLUB" <[email protected]>
Sent: Wednesday, 20 Apr, 22 At 10:59
Subject: Re: [CDV700CLUB] Need Help Modifying the Low Range Probe from AN/PDR-63
Start with this manual Steve, and identify the model # of the probe.
Geo
From: "smcarlile via groups.io" <smcarlile@...>
To: "CDV700CLUB" <
[email protected]>
Sent: Wednesday, April 20, 2022 3:26:57 AM
Subject: [CDV700CLUB] Need Help Modifying the Low Range Probe from AN/PDR-63
Hello, I have a probe from a non-working AN/PDR-63 and want to modify it to fit on a CDV-700. I do not have the book so I cannot share the schematics. I'd appreciate guidance from anyone who has done this modification. In addition, I am trying to track down a copy of the manual so I can post the schematics. Thanks Steve
