Fwd: A missive from Mike C...

Sun Jan 22 01:20:15 CST 2006

A note from Mike in the Middle East...

Sorry: I'm not going to take out all the additional chevrons from the message.
If anyone knows how to stop this happening though, please let me know. 

--- Michael Chisena <ka2zev at yahoo.com> wrote:

> Date: Sat, 21 Jan 2006 22:59:16 -0800 (PST)
> From: Michael Chisena <ka2zev at yahoo.com>
> Subject: for tacos list
> To: Iain McFadyen <mcfadyenusa at yahoo.com>
> 
> L,
>   Could you please forward this note to the taco's guys.
>    
>   Hi all,
>   Got another request.
>    
>   Been transferred to the generator shop. This is a full time slot, so no
> more worries about being laid off when the job numbers run out. In fact Ive
> been told I can stay on as long as I want to. Should I choose to extend.
>    
>   Anyhow, generator controls are not my bag, and apparently not the bag of
> the guy who was here first. Let's say I'm fixing a lot of things he didn't
> want to try. I'm from the 'lets dig the defective SCR out school' and FB was
> of "order everything the slowest way and perhaps my time here will end
> before it gets in" school.
>    
>   This guy was notorious for avoiding work. So I'm finding a lot of odds and
> ends not taken care of. 
>    
>   I'm also making contact with vendors who may be able to fix their stuff
> that I can't. Some of these controllers have 20 or more inputs and outputs.
> The Army manuals have zero data on what all these points are supposed to see
> or do. Trying to do the RMA dance now to get some of these fixed.
>    
>   One of the problems I get to have is signal generation. Many of these
> controllers monitor the output voltage of the generator and use that to
> correct for load variances.
>    
>   The prior guy used variacs w/o current limiting for this task. Not exactly
> a safe thing to do. No isolation either. Also no frequency selection. We get
> a small number of 400Hz generators in for service and there are some
> frequency selective items that won't run properly at 50Hz (Kuwait's
> frequency).
>    
>   One of the tricks used at North Atlantic Industries was making their own
> 400 Hz power for the bench. NAI made neat Phase Angle Volt Meters. Their
> trick was to have a big audio amplifier fed by an HP 200 audio Osc. I never
> forgot that trick. Seems nobody here knows of it.
>    
>   I tried this on the small scale. In down town Kuwait city I got from a
> small shop a little 15 watt audio amp kit. And at the Radio Shack a 120 volt
> to 12 volt transformer. It made just enough energy to run some of my
> circuits. That is until I killed it by accidental hooking up the wrong dc to
> the thing.
>    
>   My first question is, who is a good source for TDA 2005 audio output
> chips. 
>   I suppose any vendor that has the chips will also have high wattage zener
> diodes too.
>   If I'm so smart, what am I doing here? Part of being human is making
> errors.
>    
>   Anybody got an old PA amp for sale. Figure about 100 watts into 8 ohms.
> With that tool and my audio generator, I can make more than enough zip at 50
> to 400 Hz, and use it to check filters and some other lossy items.
>    
>   Would consider an old car stereo amplifier, police siren, or some other
> potent but cheap (lets say less than 100 dollar) audio amp that can take an
> external feed.
>    
>   If someone has one for sale, I can send you a check via my bank, and for
> shipping take it to my re mail service in McLean. (sp??) Shipping won't cost
> you a nickel.
>    
>   Also thinking of a 10,000 count DMM if anybody has one for sale. 
>    
>   My Fluke 77 works great until I try to measure the 33.4 k ohm resistors.
> That puts the range into the bottom of the scale and LSD error makes it
> difficult to see if a 1% resistor is in spec or not. It would be kind of
> cool to have a Fluke 8600 or some four wire sensing unit. I don't want to
> ask the wife to have the HP 3456A shipped over since that thing is just
> huge. I'm thinking of a Keithley or something similar. 
>    
>   If nobody has one for sale, I may have to ask the company and see what
> they have, but it would be nice to own the item at the end of the tour.
>    
>   The Heathkit tube power supply has been working out well. It's great to
> have up to 400 vdc on tap when required. Some of the relays are offset with
> 1500 ohm resistor and a bridge rectifier s in the coil path. The relay is
> supposed to turn on at a higher voltage. With my high voltage AC source KIA,
> I use the Heathkit P/S and swap the leads to get the other side of the
> bridge.
>    
>   Picked up a "Basic Stamp" learning kit. On the digital side of things, I
> have a large amount to learn. Think I figured out a project worthy of the
> unit when the learning is done.
>    
>   This place uses a lot of mil type relays. The relay tester here is a home
> brew item with a switch and a couple of light bulbs. I'm thinking of
> adapting the Basic Stamp and some other parts into a fancy relay tester.
>    
>   Some years ago I got to work on an upscale relay tester at PRD. It
> measured contact resistance into the mili ohm range, the open contact
> resistance. Twenty measurement channels. It could also be programed for N
> counts. Most of the time 5000 counts was considered a pass, and that took a
> fairly short time.
>    
>   I might be able to make a one relay at a time tester using power mosfets
> to pulse the current into the contacts, and an opamp to measure the voltage
> drop across the contacts. Since the relay in question is a dpdt, there will
> be two closed contacts, and two open contacts to measure. Another power fet
> can run the coil circuit. The run speed will be limited by how fast the A to
> D in the Basic Stamp can settle and make the measurement. Failing that I can
> run the op amp's output into a comparator and make an educated guess as to
> pass fail in milihoms. 
>    
>   On the big contactors I run three amps and look for less than 5mv across
> the contacts. 
>    
>   I will work out numbers and if I check two or three units a day with the
> thing, by the end of the month, I will beyond a doubt clear out all the
> questionable relays that the mechanics collect in their kits. As you can
> imagine relays get the blame for a lot of things mechanics can't understand,
> and I have to sort out truth from fiction.
>    
>   In other news.........
>    
>   I get a lot of comments about the little vacuum tube amplifier + mp3
> player combo. Anybody with three or more gray hairs sees the glass and a
> blast of instant nostalgia breaks out. Had a full bird in here on a tour and
> that's what he wanted to talk about.
>    
>   If anybody is interested, got the current letter home available. It's just
> too many pages for the AMRAD Taco's list. It's part news, part gripe and
> whine. Shoot me an e mail and I will do the cut and paste for you.
>   Try ka2zev at yahoo.com for best results.
>    
>   Sandy, I still owe you for the e proms, let me know how much and where to
> send please. The guilt is building up. Mental hospitals here are too cheap
> to have a rubber room, and cement is so hard on the forehead.
>    
>   That's the news dudes
>   Thanks again for your support.
>    
>   Mike Chisena aka KA2ZEV
>   Camp Arifjan Kuwait
> 
> 
> "You are, what you do, when it counts"
> The Masso

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