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Proud Mary

Sat Feb 20 2010, 10:43PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Refurbishing and recalibrating 6 Mini-Instruments Mini-Monitors Mod 5.10 GM Counter, and 1 Mini-Monitor Scintillation Counter Mod 5.40 which I bought for very little in an auction of government junk.

So far, I have replaced three rotary wafer switches, three rocker switches, one leaky electrolytic and two resistors that had changed their value. I've also stripped the cases down to bare metal and have applied coats of red oxide and grey metal primer, which will be finished with Hammerite blue hammer finish in keeping with the original design.

The tube voltage can be varied between 350V and 700V by a pot on the PCB board, while re-calibrating is done by injecting a pulse stream from a function generator into the rate-meter circuit, and adjusting two pots to get the best match for 100pps and 1000pps on the meter scale.

The Mini-Monitor has been the great workhorse of decontamination, education, and radio-medicine in the UK for about thirty years, and is very repair friendly.

I already have one of the yellow and black 900 series Mini-Monitors with a gamma/uSv scale, so I shall optimize three of this lot for X-rays, beta-gamma, and alpha respectively, and give the rest away to friends, as I simply have no more space for equipment and parts in my small home!

Fitted with a Centronics B12N glass GM tube, the Mini-Monitor can detect the extra gamma counts due to a small chunk of pitchblende placed 150cm from the tube.

I have cribbed this photo off the web, as mine are exactly the same except in the GM tube case, where I have several different designs to cope with end-window GM tubes.

MinorityCarrier

Sat Feb 20 2010, 10:55PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Because of where I work, I get freebie power mosfets and IGBT's, engineering runs and parametric outliers that can't be sold, so I'm building a HTGB/HTBV HV burn-in test station.
I want to use digital panel meters for displaying high voltage current, so I am building a rack display with digital meters in a faraday cage and built a 24VDC-to-5VDC regulated 10KVDC-isolated power supply to run the meters.

The first two photos are of the acrylic assembly housing the digital meters in the faraday cage, and the 10KVDC-isolated DC-DC power supply.

The last photo is of a 12VDC to 350VDC 200ma DC-DC converter for a project I'm working on aimed at repelling dogs that attack me while I'm riding my mountain bike.

Steve Conner

Sun Feb 21 2010, 10:36AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

MinorityCarrier wrote ...

HTGB/HTBV HV burn-in test station.

HTGB, HTBV? Just curious, what are those?

wrote ...

I'm working on aimed at repelling dogs that attack me while I'm riding my mountain bike.

Ride faster :)

MinorityCarrier

Sun Feb 21 2010, 06:39PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

High Temperature Gate Bias & High Temperature Breakdown Voltage.

Basically heating the devices to 120C or 150C with a stress voltage applied for an interval of time.

For HTGB, a measurement of Vt is taken before and after the stress. during stress, the gate is biased relative to source, usually at 25V, (our gate oxide Bv is rated at 50 volts). If the Vt shifts much, there may be mobile ion contamination (rogue charge) in the gate oxide or some other problem. Repeating the test with gate-source voltage reversed is also performed to see if Vt can be returned to its original value.

For HTBV, the dervice is biased near avalanche then the leakage current is monitored while the device is elevated to stress temperature and kept there for awhile. If the leakage current climbs too high, it could mean something with the processing was defective, in field termination, with channel stop implants, etc. If the device goes into avalanche during the test, I don't want to use it. If enough devices of a run go into avalanche, I throw the whole run into the company reclaim drum.

Dr. Drone

Sun Feb 21 2010, 11:56PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Dave Marshall

Mon Feb 22 2010, 04:00AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

I'm actually working on a very large project that is broken down into a number of smaller ones.

I run a large storm chasing team here in the US, and I'm hoping this year is going to be a particularly good one for storms. As such I'm completely rebuilding the electronic systems in my pickup truck. Photos will be coming soon, but it will include a touch-screen laptop in the console, another onboard computer for streaming video, an HF/VHF/UHF amateur radio system using at least 3 radios, and a number of other little tweaks and gadgets, all of which I'm tackling as solo projects.

Should keep me busy until the season really gets rolling here in late April or early May.

-Dave

rp181

Mon Feb 22 2010, 04:38AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Sounds awesome Dave, would be awesome to pictures of your truck!

As for me, still working of the railgun. Im just about done with it, I am going to try to sell it to fund a new project: autonomous 6WD ground vehicle (terrain capability of focus, along with artificial neural networks and image analysis). The entire platform will be ~2 feet long.

dmg

Mon Feb 22 2010, 06:37AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

awsome projects, thank you for sharing those

Zeus

Mon Feb 22 2010, 10:41PM

Registered Member #2316 Joined: Tue Aug 25 2009, 03:04AM
Location: Bendigo, Australia
Posts: 107

I would be working on the design for a quad-band modular yagi, but I can't get MMANA-GAL to work.
350V 200mA DC-DC converter to discourage dogs, Hmm I think you shall be popular with the Aztecs.
All the same I would like to see that schematic, Is it a boost converter, push-pull transformer or maybe
a flyback topolgy.

MinorityCarrier

Mon Feb 22 2010, 11:44PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Its a saturation-limited push-pull using MJE3055's and a Triad/Utrad TY-79 transformer. I got the transformer secondary voltage wrong, its only 300 V not 350. Obtained a handfull of these transformers years ago, along with some TY-92's. Used them for strobes, cap chargers, etc, great fun. I believe their original intent was for plate supply in vacuum tube auto radios, to replace the electromechanical chopper design.

I'll post the schematic this evening if you wish.

(P.S. I don't think Aztec dogs, the Mexican Hairless or Chihuahua, would have anything to fear from me)

UPDATE: Here's a schematic of the DC-DC converter in the photo (minus the 450V electrolytic).

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