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 Second GMC-320 plus with SBT-11A
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Alchemy2

Canada
87 Posts

Posted - 09/27/2014 :  21:53:29  Show Profile  Reply with Quote
I just finished my retrofit of my second GM unit, and it works great!

I mounted the tube off the battery slot, and moved the battery to where the tube was. I used a short piece of RG-174/U cable to connect the tube direct, no additional resistors needed. I also had to dremmel out the slot where the old tube sat to allow my battery to fit properly inside the unit.

After some fiddling, we got it done! It looks pretty neat after mounting a small piece of Lund screen to protect the tube from damage!

The unit picks up now, bremsstrahlung from a small tritium keychain lite I had. Nice! Background is very low, still in the 18-30 CPM range.

WAY more sensitive than the stock M4011 tube, and I kept the old one as a spare for my first unit. I am using 270 CPM/uSv/h as my initial sensitivity. (SBT-11A claims 44-49 cps/mR/h). So I took the mean. I will check it later on with my calibration samples.

Nice...

More to come.

The more I learn, the more I realize I do not know!

Edited by - Alchemy2 on 09/27/2014 21:54:57
Reply #1

ZLM

1055 Posts

Posted - 09/28/2014 :  19:29:51  Show Profile  Reply with Quote
Good. Pictures please.
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Reply #2

Alchemy2

Canada
87 Posts

Posted - 09/29/2014 :  21:42:00  Show Profile  Reply with Quote
Okay, second try!

Pix:

Image Insert:

125.16 KB

Basically, I mounted the SBT-11A tube by the battery cover and moved the battery to where the previous tube (M4011) was. I used RG-174/U coax for the tube connections to the board clips. No additional resistors required. Tube runs nice and quiet and is more sensitive and also responds to both alpha and low E X/gamma (<18keV Bremsstralung (X rays) from the low E betas off a tritium tube). I get around 80 CPM with the screen in place, vs 110 without it. I epoxied the tube to the back case, and same with the screen to protect the tube. The battery cover after trimming with a Dremmel was adhered using CA glue. The main board where the stock/old M4011 tube sat was carefully cut back by ~8mm to give more room for the battery size. It is tight getting together, but is good.

Another pic:


Image Insert:

79.02 KB

All in all, this was a great retrofit for unit #2 - more sensitive and better all around suitability to general samples. I get >4500 CPM on a Thorium sample which only reads around 900CPM with my unit#1, with stock 4011 tube.

For that fellow wanting low/soft X-ray responses, this would be a good choice! I get <18.6 keV! Tube should read soft X-rays to at least around 5 KeV now...

Alchemy2

The more I learn, the more I realize I do not know!
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Reply #3

ZLM

1055 Posts

Posted - 09/29/2014 :  22:25:39  Show Profile  Reply with Quote
It looks really cool.
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Reply #4

Alchemy2

Canada
87 Posts

Posted - 09/30/2014 :  20:24:50  Show Profile  Reply with Quote
THanks!

Yes, and it still remains handheld :)


The more I learn, the more I realize I do not know!
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Reply #5

CuaC

Germany
3 Posts

Posted - 04/23/2016 :  04:46:03  Show Profile  Reply with Quote
quote:
Originally posted by Alchemy2

I just finished my retrofit of my second GM unit, and it works great!

I mounted the tube off the battery slot, and moved the battery to where the tube was. I used a short piece of RG-174/U cable to connect the tube direct, no additional resistors needed. I also had to dremmel out the slot where the old tube sat to allow my battery to fit properly inside the unit.

After some fiddling, we got it done! It looks pretty neat after mounting a small piece of Lund screen to protect the tube from damage!

The unit picks up now, bremsstrahlung from a small tritium keychain lite I had. Nice! Background is very low, still in the 18-30 CPM range.

WAY more sensitive than the stock M4011 tube, and I kept the old one as a spare for my first unit. I am using 270 CPM/uSv/h as my initial sensitivity. (SBT-11A claims 44-49 cps/mR/h). So I took the mean. I will check it later on with my calibration samples.

Nice...

More to come.



I have just installed an SBT 11a in my 320plus, did you finally test the tube against your calibration sources? which values did you get?
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Reply #6

Distelzombie

Germany
176 Posts

Posted - 04/25/2016 :  13:20:24  Show Profile  Reply with Quote
Yeah. I would like to know them too.
Let's hope he's looking into this forum from time to time. :)

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.
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