My Bicron "Labtech" camp fire story

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Richard Hull
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My Bicron "Labtech" camp fire story

Post by Richard Hull »

I recently acquired a Bicron Labtech from a friend. He said that the last time he used it, some years ago, it was working. He forwarded it to me via UPS for test and inspection and once the condition was determined, we would talk price.

I attach images and you can refer to them in conjunction with the text.

The labtech is a nice plus ultra unit that can accept GM detectors or PMT gamma detectors. It can window specific gamma signatures of isotopes. My unit is a special Labtech not found in the literature. It has a side arm and an internal Bicron 10 stage, 2-inch PMT with a 1.25 - inch crystal holder. The large side arm, screw on canister is a mystery I have not figured out yet. The crystal stub protrusion allows for a 0.1 inch thick aluminum shield to stop very low energy background gammas. The unit came without a crystal, but a nice internal, 10 stage Bicron PMT. Cool beans. I would ultimately mill and machine a Bicron BC 400 plastic Scintillator for this little stub chamber out of about 30 lbs of various Bicron Scintillator plastic I obtained 10 years ago from Don Orie.

Telling the tale............

I recieved the unit with a broken shaft on the main function selector. Broken in shipment due to weak packing. (see first image) I called and my friend said we would adjust accordingly if I still wanted it. I accepted his offer. He said fix or replace the switch and finish my check out. The aluminum case body was also very shop worn with paint scratches and nicks from years of use somewhere.

The switch had a weird switching pattern and was of a custom design. (I obtained a rough schematic online) I decided to attempt repair. The swicth was of the PC board mount type and was a molded plastic unit with no visible wafers for me to noodle out...(@$#%#@*).

I had to break the thing down to its skivies and the switch was sandwiched between two large PC boards attached via all the controls to the front panel that I had to separate. (#%$&*(!!%^) They were connected by a 30 pin through board, pin system at one end and a similar 16 long pinned assembly at the other. To make matters worse, a 28 pin ribbon cable went from these to the main power and amp board in the base of the Labtech. (#@^%&*$) Lots o' pins to break and bend in disassembly and reassembly. I had to get this right on the first pass.

Once the damaged switch was desoldered and removed from the board...The first easy thing I had to do...... I found that I would have to pop the seam on this switch to noodle out the pattern. BAD...BAD idea..... Upon popping the seam and carefully separting the switch, all 20 pins on the switch fell out on the table! SUPER #$@#$%*&&($!!@. They looked all different lengths and angles...What a royal mess!

Steeling myself to what would be a 4 hour task, I noted that there were two of each type of pin and contact arm, (ten pairs) Well, at least things were symmetrical.... Should help on reassembly a bit.

To my amazement, there was only a silvered metal disk on the shaft! Upon this disk was a keyed polyethylene disk of the same size with square holes cut in it of various sizes in circular orbital patterns around the disk. I began to see the beauty in the design and the ugliness of my task. This was a simple switch with 20 contacts of idential contact arms reaching over the various orbital paths such that, in rotation, various wipers extending from the various PC board pins would drop into programmed holes in the PE disk and make contact via the silvered conductive disk. One switch would only need a customer's special swithcing needs for each postion translated into corresponding holes in a single small PE disk! Sweet idea.

Now, to figure out the repair of the shaft. It would be a fool's errand to super glue the non-super glue friendly shaft back together. The first resistant turn and it would snap. (#%$*&()!##$) I could not replace the shaft as it was molded to the metal disk (#$%^$*&). Repair, it was going to have to be. The first job was to temporarily glue the shaft together for the coming work, which I did.

Fortunately, I am a model railroader and commonly have to bore, tap and thread #2, #1, #0 and #00 shafts and holes. I have all the hardware on hand. I found an #0-72 screw of a suitable length. Next, I bored a tap hole through the center of the shaft to a depth through the glue joint and beyond. I tapped the hole and put super glue on the long screw and rapidly screwed it all the way in. It locked up just shy of full insertion, but enough to grab both halves of the shaft. SHAFT FIXED!!........Now, to put this pig back together so it works! A full day ++ had now passed in the effort, so far. Ain't retirement great! I hit the sack at 3:15AM to attack the reassembly in the morning.

The new day dawns and I figured out the layout of the contact pins in under 20 minutes. (fresh brain) The pins had little slots they fit in on the molded body, but I found that I would have to place the tiniest drop of super glue in the slot to hold the pin for re-assembly. It was imperative to use the smallest amount as the near super-fluidity of super glue might wick out to the contact wiper and foul the swithcing action. By noon I was ready for reassembly and testing. The two halves went together smoothly and I used small clamps to hold the item together for ohmic testing. by 2PM the switch was tested and molded via remelting along the edges. by 4pm I had the switch resoldered into palce and the boards reassembled and mounted back onto the front panel. Working the switch wildly showed the shaft to be fully restored and secure. Now to put it in manual mode and turn on the unit.

I left the thing more or less in a loose, but insulated and fully connected shambles. POWER ON! The LEDs all lit fine, but within 5 seconds went out. WHAT FRESH HELL IS THIS!!! The fuse was good. A look at the schematic showed the regulator was an LM317 which I know to be automatic thermal shut down on short. Ohmic check of the 12v buss showed a short to ground. Looking over the main board in the belly of the beast, I spied the evil gum drop tantalums of NIM module infamy. I pulled one or two and replaced them, until a third one tested short. I replaced it and two others that were in the circuit.

POWER ON! All circuitry seemed good and stayed on with a glowing LED display looking good. I put the entire rig back together. BAD MOVE! As I went through the modes on the repaired mode mode switch all was good. Back to manual mode and now to plug in my pancake probe and set the HV to 800 volts. WHAT?! No HV indication at all. Is it a meter circuit problem? NO! It turns out the oscillator to the step up transformer was not working. It was now nightfall of the second full day of work on this rig. Despondent, I went into the house for dinner and a full evening of mind rotting TV. My first laughter in days as a marathon of old Big Bang Theory shows was just what I needed.

The third day dawned and after about 2 hours I had replaced one IC and two diodes and the High voltage was up. Another 30 minutes was consumed putting it all back together again. Now, I tested the system and all was 100% across the board. The GM worked great and the counter worked, the timer worked the 2 channels of windowing worked. So after a full hour of this testing, I went in for a late lunch at 2 PM. I had always planned to repaint this orphan so when I came back out, I changed back to a GM probe and wheeled the multiturn pot back to zero, turned the unit on and as I raised the voltage, nothing happened on the meter. (@#$%^@#$) I tapped the main board and the meter slammed over to 2500 volts! YIKES! Taking my probe off the BNC jack, I started it back up and as I tapped the board, the voltage went from no reading, to pegging and to the proper voltage. Holding the board down in this latter manner showed full control of the voltage. I HAD AN INTERMITTENT CONNECTION ON THE MAIN BOARD. (#@$%^&%$**).

Out comes the board, yet again! I spent one hour resoldering all components and ICs on the board with fresh solder. With it all still apart, but connected and insulated, I turned it on and all was good. Whacking on the board had no effect and the voltage reading was stable. The third day came to an end and painting was reserved for day 4.

As the unit was already partially dis-assembled it took about 1 hour to prep the top and bottom halves for painting. Painting was over in under 20 minutes. While the painted case halves were drying, I decided to muse over the shiney, chromed, Bicron internal 2- inch PMT and mating base. With no crystal, it was useless and untestable. I had tested the Lab tech earlier with one of my sodium iodide 3" units and it worked fine and I windowed both Cs137 and Am241 just fine, Thus, I knew all was OK, electronically, for any PMT. I decided to use a tiny piece of my 30 pounds of scintillation plastic on hand. I milled and machined a perfectly fitting cylinder of Bicron BC 400 plastic. I polished one end to total clarity.

Yet a new day would dawn, (day 5) and I reassembled the dried case and all components. I dropped in the scintillator and just pressed the clear end against the internal PMT face using only the faom pad in the base of the threaded aluminum retainer cup for pressure. At about 1100 volts in manual mode I got a good steady clicking. A piece iof U ore brought to the aluminum stub made the thing really sing with a rush of noise and the counter loaded a kilocount a second, while the meter pegged. IT WORKS!

After about 40+ hours of work, I had a new looking, perfectly functional, Bicron labtech of a special release type with internal PMT. The unit was not yet mine and based on my effort, I called my friend and said that if he sent me a check for $800.00 I would take the unit. We both laughed, realizing this was a love's labor on my part. After telling him the saga, he said to just send him $100.00, which I did the next day.

Some times your eat the bear and sometimes the bear eats you................

Check out the finished images. Click to enlarge

Richard Hull
Attachments
Close up of broken knob.  What a chore lay ahead.  Seemed easy at first.
Close up of broken knob. What a chore lay ahead. Seemed easy at first.
Overall view of the finished Labtech
Overall view of the finished Labtech
second overall view
second overall view
the dual channel windowing control.  Center is manual PMT or GM mode
the dual channel windowing control. Center is manual PMT or GM mode
Odd side arm canister....What is it for?
Odd side arm canister....What is it for?
PMT stub chamber for the scintillator
PMT stub chamber for the scintillator
PMT port
PMT port
Plastic test scintillator and mount
Plastic test scintillator and mount
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
George Schmermund
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Real name: George Schmermund
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Re: My Bicron "Labtech" camp fire story

Post by George Schmermund »

Richard - If the plastic in your photo is any of the Bicron 400 series scintillators, it should be water clear with a tinge of blue in some lighting situations. The yellow cast is a sign that the plastic is very old and it's not going to work well, if at all.
Anything obvious in high vacuum is probably wrong.
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Richard Hull
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Re: My Bicron "Labtech" camp fire story

Post by Richard Hull »

The plastic shown is not my piece, but an old piece I had on hand to run a crude first test that I did not mention. I did not want to take the 3 hour job of milling from good BC-400 if the PMT was shot! This junk piece worked well and showed I had a viable PMT.

All of my scintillation plastic is of the blue-violet cast due to rayleigh scattering by the scintillator additive and is prime good stuff. I also have a large stock of various NE grades as well.

I cut an oblong, 1.5-inch square block out of a bar of BC-400 about 12 inches long by 3 inches wide and 1.5-inches thick. I milled the sides square and parallel. Next, I placed it in a four jaw chuck and machined it into a cylinder that was a perfect fit for the aluminum well stub. I cut to proper length and then, I fine finished the resultant cylinder ends with hair fine cuts. Next, I hand wet sanded one end from 600 thru 1800 grit fine and finish polished with wet Barnesite to crystal clarity.

To others...This fine organic scintillator that I made up is only good for detection and can give no useful fine windowing such as found in a formal inorganic crystal like NaI:Tl.

The junk, lop-sided, test scintillator cylinder was from a box of nuclear dept stuff discarded by UNC that I purchased at the Raleigh Hamfest a few years back. It was just under 1 inch and fit loosely, but was good enough for that first pass test.

I did not photograph my good cylinder as it is now properly optically coupled to the PMT with coupling grease.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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