Today's Dubious Use of Time and Money

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SteveHGraham
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Re: Today's Dubious Use of Time and Money

Postby SteveHGraham » Tue Apr 18, 2017 1:15 pm

I don't agree that solid state electronics are shockproof. If I threw one of my Chinese meters on the floor, the dial would come off, the case would shatter, and God only knows how many connections would break.

I'm sure it's tougher than the old meters with tubes and cooling fans, however. But to throw one of those on the floor, you would first have to be able to lift it.

All this being said, I lost a lot of my enthusiasm for Fluke products when I learned about used Ebay bench meters. They don't fall over. They have big, bright displays. And no batteries to change!
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John Hasler
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Re: Today's Dubious Use of Time and Money

Postby John Hasler » Tue Apr 18, 2017 1:28 pm

The electronics (that is, the circuit boards, not the cases) aren't shockproof but they are fairly shock-resistant. No connections would break unless the case shattered (quite likely with a flimsy Chinese meter, of course). It doesn't cost hundreds of dollars to provide a tough case and some padding. Fluke has competitors who do as at much lower prices.

I wasn't talking about VTVMs like my RCA Voltohmyst (which I've converted to use an op amp and batteries): more like my Simpson. The passive components and switches inside are about as sturdy as those in a modern meter but the jeweled meter movement is fragile: no way around it.

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BigDumbDinosaur
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Re: Today's Dubious Use of Time and Money

Postby BigDumbDinosaur » Tue Apr 18, 2017 1:58 pm

warmstrong1955 wrote:You should see what happens to a Simpson when it falls on a muckpile from about 15 feet......
Or when they make a splash in the water when you are wiring in a Flygt 58 in a rubber raft.

:)
Bill

In the Navy, we had the PSM-4, which was a militarized version of the Simpson 260 analog multimeter. It was water-proof and could actually float if dropped overboard, not that I ever did anything like that (one of my buddies did, however).

I was up on the mast one time fixing a problem with a UHF antenna when I lost my grip on my PSM-4 and dropped it. It just missed going down the forward funnel and landed on the torpedo deck some 30 feet below where I was perched. I climbed down to retrieve it, expecting to find the thing all smashed to hell. I was astonished, to put it mildly, to discover that it was still functional and that the meter movement had survived the shock of bouncing off the side of a torpedo tube before landing on the deck. The only damage was a crack in the side of the case, which meant it was no longer waterproof. :D
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John Hasler
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Re: Today's Dubious Use of Time and Money

Postby John Hasler » Tue Apr 18, 2017 10:37 pm

BigDumbDinosaur wrote:
warmstrong1955 wrote:You should see what happens to a Simpson when it falls on a muckpile from about 15 feet......
Or when they make a splash in the water when you are wiring in a Flygt 58 in a rubber raft.

:)
Bill

In the Navy, we had the PSM-4, which was a militarized version of the Simpson 260 analog multimeter. It was water-proof and could actually float if dropped overboard, not that I ever did anything like that (one of my buddies did, however).

I was up on the mast one time fixing a problem with a UHF antenna when I lost my grip on my PSM-4 and dropped it. It just missed going down the forward funnel and landed on the torpedo deck some 30 feet below where I was perched. I climbed down to retrieve it, expecting to find the thing all smashed to hell. I was astonished, to put it mildly, to discover that it was still functional and that the meter movement had survived the shock of bouncing off the side of a torpedo tube before landing on the deck. The only damage was a crack in the side of the case, which meant it was no longer waterproof. :D


Sounds like those PSM-4s were made with sailors in mind. Over the years I've managed to bugger up several meter movements by dropping them from much lower heights or whacking them in other ways (I did manage to fix some of them).

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BigDumbDinosaur
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Re: Today's Dubious Use of Time and Money

Postby BigDumbDinosaur » Wed Apr 19, 2017 1:13 am

John Hasler wrote:Sounds like those PSM-4s were made with sailors in mind. Over the years I've managed to bugger up several meter movements by dropping them from much lower heights or whacking them in other ways (I did manage to fix some of them).

Everything on that ship seemed as though it was designed to take serious abuse. Particularly interesting were the methods used in electronic equipment to protect tubes from damage. Most of this stuff was shock-mounted and tubes were positively retained in their sockets so the shock of firing the main guns wouldn't cause them to unseat. Despite all that, we'd occasionally have a piece of gear conk out after simultaneously firing all of the main guns. The tremendous shock kicked back into the hull would find tubes that were marginal and finish them off. :twisted:
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John Hasler
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Re: Today's Dubious Use of Time and Money

Postby John Hasler » Wed Apr 19, 2017 11:14 am

BigDumbDinosaur writes:
> Particularly interesting were the methods used in electronic equipment to protect tubes from damage. Most of this stuff was shock-mounted and tubes were positively retained in their sockets so the shock of firing the main guns wouldn't cause them to unseat.

Yes, the tank radios I serviced at Fort Knox were built that way. The tank main guns weren't nearly as hard on the equipment as the tankers were, though.

The complex series-parallel schemes used to run the low-voltage filaments from 24VDC made finding the open filament tedious.

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BigDumbDinosaur
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Re: Today's Dubious Use of Time and Money

Postby BigDumbDinosaur » Wed Apr 19, 2017 2:53 pm

John Hasler wrote:The complex series-parallel schemes used to run the low-voltage filaments from 24VDC made finding the open filament tedious.

Fortunately, we didn't have that problem aboard ship. It was the typical parallel filament setup connected to a 6.3 volt CT transformer secondary.

What was interesting was the use of three-phase bridge rectification to produce B+ voltages in the radio receivers. In the mid-1960s the Navy was starting to get some hybrid gear that used solid state rectification to produce B+. As power on the ship was distributed as 480 volt, three-phase, it could be directly rectified in some cases to generate the appropriate DC. With a ripple frequency of 360 Hz instead of 120 Hz, the B+ was a lot cleaner and needed much less filtering. However, if one of the diodes opened up, a phase would be dropped and the power supply would produce really dirty DC because so little filtering was present. The radio was essentially useless when that happened. It wasn't a good place to have to stick your hands while power was applied to do some troubleshooting... :shock:

More fun was fixing radar transmitters. Our air search radar pumped a maximum of 750 kilowatts into the antenna, making it possible to detect high speed aircraft over 300 miles from the ship. The final power tube that drove the antenna, a water-cooled tetrode the size of a scrub bucket, operated with 25,000 volts on the plate when at full power, with about 55 amps of plate current. The final was pulsed by a thyratron that was about three feet tall and operated at a mere 4500 volts. Needless to say, I was very cautious around that radar unit. At those voltages you didn't have to make contact to make contact. :twisted:
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tornitore45
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Re: Today's Dubious Use of Time and Money

Postby tornitore45 » Fri Apr 21, 2017 3:19 pm

Opened it up and found a tiny 3.15-amp fuse (Why not 3?)


Excellent question!
Look at: https://en.wikipedia.org/wiki/Renard_series

You will notice that 3.15 is in the second column while 3 is in the fourth column.

For sake of standardization and inventory minimization the first, sparser, column is to be a preferred choice and denser and denser columns with more intermediate values are considered less preferred.
In the early days of electronic preferred values were a little less expensive, today quantities are so high it does not matter.

Since these series are all based on a modulus derived from a N-root of 10, N being either a multiple of 6 or 10 the resulting value have a good chance of being irrational or at least with many digits.
All this was wonderful until somebody started building Rseries based on 12 like R12 and R48 and beating the results into a 3 digits approximation and then beating them some more into 2 digits for the most sparse serie R6.

Now ya now.
Mauro Gaetano
in Austin TX

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SteveHGraham
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Re: Today's Dubious Use of Time and Money

Postby SteveHGraham » Fri Apr 21, 2017 5:19 pm

My hat is off to you for knowing something that obscure.

The amplifier is working fine with a 3-amp fuse, because I was too immature to wait three or four days for 3.15-amp fuses to arrive.

Here's something weird. I was wrong about the fuse being blown. The filament in the fuse had a blob of metal in the middle of it, so I assumed it had melted and refused in a blown state. I didn't bother checking it. I just looked at it through my $1.00 reading glasses. I checked the resistance a few minutes ago, and it's not infinite, so the old fuse is okay. Apparently, it's a type of slow-blow I'm not familiar with, and the blob is part of that.

So now I wonder...why did it stop working, and why does it work now that I replaced a good fuse? The wall wart checks out, and the switch seems okay.
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tornitore45
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Re: Today's Dubious Use of Time and Money

Postby tornitore45 » Fri Apr 21, 2017 5:56 pm

The only thing I can think is that the fuse holder clips oxidized and your actions scraped them clean enough.
South FL humidity and salinity can do that.
That is my story and I stick with it.
Mauro Gaetano

in Austin TX

Harold_V
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Re: Today's Dubious Use of Time and Money

Postby Harold_V » Sat Apr 22, 2017 1:23 am

Hmmm. Not infinite? As if implying that there is resistance, but not an overwhelming amount of resistance?
If so, the fuse IS the problem, as it should display very little resistance. Well under one ohm.
The blob you witness is the result of the blown fuse, as you alluded. What may have happened is a flash of metal deposited inside, the results of the arc created when the fuse blew. That can result in very high resistance continuity.

The condition mentioned, above, has been an experience I've had on a couple occasions, when the micro-switch in the joy stick of my Graziano erodes enough to cover the switch innards with a fine metallic deposit. The result is for the spindle to start at random. I shudder to think what would happen (three horse motor) if that were to happen while tightening the chuck.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

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SteveHGraham
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Re: Today's Dubious Use of Time and Money

Postby SteveHGraham » Sat Apr 22, 2017 10:22 am

I don't actually know what the resistance is. I was looking for an open circuit, so when I didn't get infinite resistance, I dropped the test leads without paying attention to the number. I can look at it again.

The blob is a "feature" of this type of fuse. I was looking for replacements on the web, and I saw a brand-new slow-blow fuse with a blob.
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