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Warning: Turn down gain before switching input

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10/6/2010 04:05 AM EDT

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FWB
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re: Warning: Turn down gain before switching input
FWB   11/25/2010 2:53:15 PM
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Some engineering took some doing. A rugby feed from UK to New Zealand first time had the players followed some distance by the color of their uniform. Group delay equalizers were needed. The feed from the US had to go through a Rank analog TV standards converter which took 3 racks and used crystal delay lines for interpolation. Both are probably no longer documented designs, but they are how we got to where we are now.

Diseased
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re: Warning: Turn down gain before switching input
Diseased   11/25/2010 3:04:44 AM
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Sometime back, more years than I care to consider, I was a young engineer part of a team developing a sonobouy receiver for the Navy's S3A aircraft. The specifications were tight enough that we had an interesting time with the crystal filter designs. By the end of the project these and the entire RF chain were my sole responsibility. I'd managed to specify some rather nice filters and they worked nicely. To prove the filters I'd developed a nice test board and some procedures that got me past some of the limitations of the then current spectrum analyzers that plagued anyone without a tracking signal generator. So we really had good equipment to deliver to the Navy. So we built the prototype. Somewhat predictably for the era we found a problem or two and generated tiny work arounds for them. Then we ran preliminary tests and it worked like a champ. Finally we entered the qual testing phase. This involved a large shake table, LTV I believe. We sailed through the shock and vibration tests. Unfortunately these were not the last tests to be run on that ill fated receiver. The test technician at the shake table facility accidentally pulled the signal source before cutting power. The predictable rather extreme shock rather rattled the receiver's brains. Some of the 31 receivers failed on the spot. So I had to pull all the boards and find the good ones and replace the bad ones. The failures often were not "instantaneous", which if memory serves led to replacing ALL the boards. I watched one fail under retest. It looked fine one moment and showed garbage moments later as another crystal departed from one of its mounting leads. This would have been late in the ASR33 era (about 1970). So I guess the shake table people took a long time to learn about click and pop filters. I feel your pain, Charles. {^_^}

Stargzer
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re: Warning: Turn down gain before switching input
Stargzer   11/24/2010 11:59:15 PM
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There once was a Star Trek game in BASIC that depended on the Model 33's timing of the auto carriage return / line feed. The PRINT statement centered the title words "S T A R T R E K" but left out one of the characters, printing it as the 73rd character of the 72-character line. If the ASR was set up for auto carriage return, it did a return before a line feed, and the missing character was printed as the print head returned, before the line feed (the original bi-directional printer!). Some software was set up to put out two CRs before the LF to make sure the print head was all the way back to the left. If the auto carriage return was not set, all the characters after 72 piled up on the 72nd character.

Butch Weber
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re: Warning: Turn down gain before switching input
Butch Weber   10/28/2010 8:09:10 PM
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This brings back many fond and not so fond memories. I hated being a teletype repairman in the US Navy, but I like typing on them. I was a Radioman and we used mostly the model 28s. When I got out of the Navy I found an old Kleinschmidt table top teletypewriter. It was something to behold. I used it on Ham Radio for many years before going electronic. What Fun!

WKetel
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re: Warning: Turn down gain before switching input
WKetel   10/17/2010 1:57:21 AM
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I didn't get to play with the ASR, but I certainly had to run quite a few shake tests on vehicle bodies and parts of cars, all using those old tube type amplifiers. They were indeed very impressive, and they could produce fast transients, with far more than their rated output, for two or three seconds, which was plenty of time to do a whole lot of damage. So we would start with the gain control at minimum every time. Of course, some of the testing was done with a feedback controller, either holding constant force with a force sensor in the drive link, or with constant velocity, using a displacement sensor, and recording the force, which drops as resonance is approached. That can be exciting, I have seen a pickup truck broken just by driving it at the resonant frequency for a few minutes. It was quite a show.

daveismissing
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re: Warning: Turn down gain before switching input
daveismissing   10/14/2010 1:19:18 PM
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'28s and '29s? were the Cadillac designs.Indestructible. 32's (5 level) and 33's (8 level) were brilliant from a low cost design POV. Fresh out of electronics curriculum I spent my first 6 months with the local "Telex" carrier R&R'ing machines, Freon baths, re-grease, disassemble clutches, checking clearances, replacing contacts. Feeler gauges and a voltmeter! 33s pretty much operated at their mechanical limits, fussier that 32's IIRC.

NevadaDave
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re: Warning: Turn down gain before switching input
NevadaDave   10/13/2010 7:17:36 PM
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Actually, looking at some old pics now that my interest has been piqued, I think we used the Model 28 back in the late '60's/early '70's when I was in the Guard.

NevadaDave
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re: Warning: Turn down gain before switching input
NevadaDave   10/13/2010 7:03:49 PM
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Oh, man! I remember using the old mechanical Teletype machines when I was in the USCG. It may be apocryphal, but when we were in tech school, we were told that the designer of the model then in common use (I don't remember the number maybe the 23?) was a mechanical genius who eventually committed suicide. Watching those machines work was absolutely fascinating, and makes me even more appreciative of modern comm devices. I also remember acoustic-coupled 110 baud ASR33 machines talking to our IBM 370 many years ago. Now I complain if my connect speeds are lower than 1.5 mbit!

CharlesGlorioso
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re: Warning: Turn down gain before switching input
CharlesGlorioso   10/13/2010 4:26:13 PM
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All great comments about ASR33 Teletypes, and early computer usage of them. (By the way "Teletype" is a registered trademark of the company by that name. Like Kleenex, they had such a high market share that they almost lost their trademark due to common usage.) Those Model 33 devices were designed for light duty usage in Telex and TWX (Telegram) usage. But they hit the market at exactly the right time for use in the first time sharing computers, as described by Mtripoli. As a result they were a much more successful (profitable) product than planned. Charles

Itinerant Engineer
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re: Warning: Turn down gain before switching input
Itinerant Engineer   10/12/2010 10:07:56 PM
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My father was a communicator in Civil Air Patrol (CAP), the USAF's poor relation, which always had to make do with hand-me-down equipment. Over the years, we had several TTYs in the basement; their racket was a familiar, even comforting sound. Since the machines had attached punched tape readers, Dad created several loops of tape with routine message headers, etc., with the drive holes cut out at points where he would insert message-specific information. When the machines wore out beyond repair, upon decommissioning, he'd give them to me to tear apart. I had a wonderful collection of micro-switches and other state-of-the-era parts. Lance ==)--------------

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