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"William Sommerwerck" <grizzledgeezer@comcast.net>: Dec 20 05:06AM -0800 Error! Error! Error!   My fault. The article about integrated amp/speaker systems //was// the article I was looking for. I had conflated it with photographs in KLH user manuals.   Looking at old magazines sure brings back memories -- and provokes a lot of laughs -- and I'm not talking about John Frye's short stories.

"Tom Miller" <tmiller11147@verizon.net>: Dec 20 06:43PM -0500 "Lee Gleason" <lee.gleason@comcast.net> wrote in message news:5495f247$0$13196$882e7ee2@usenet-news.net... > Lee K. Gleason N5ZMR > Control-G Consultants > lee.gleason@comcast.net I would recommend going through the adjustments section of the service manual. That will offer you a chance to find any out-of-spec parts. The Tek manuals are very complete and include a theory of operation section that will answer most questions. Pay attention to the ripple/noise specs on the power supply test points. The +55 volt rail serves as the main reference for the rest of the supplies.   Regards

amdx <nojunk@knology.net>: Dec 20 04:23PM -0600 On 12/20/2014 4:03 PM, Lee Gleason wrote: > Lee K. Gleason N5ZMR > Control-G Consultants > lee.gleason@comcast.net   There's a good TEK yahoo group that might be helpful.   Mikek

RobertMacy <robert.a.macy@gmail.com>: Dec 21 09:48AM -0700 On Sat, 20 Dec 2014 15:03:27 -0700, Lee Gleason <lee.gleason@comcast.net> wrote:   > Lee K. Gleason N5ZMR > Control-G Consultants > lee.gleason@comcast.net     Did you ask the TEK group?   <TekScopes@yahoogroups.com>   I saw some detailed info go by there, often.

Tim Schwartz <tim@bristolnj.com>: Dec 21 08:49AM -0500 > So I next got out the Strobeotac and put it on the motor capstan. The motor is rated for 1850 RPM at 115V, and it's running rock solid at 1795. I tried loading it while watching the speed and it remains steady, so it doesn't appear to be a load problem. Could such a slight motor speed reduction cause a 25 percent reduction in the frequency of my 1KHZ test tone off the tape? It doesn't seem possible, but I don't know.   > The motor has a label that reads that it uses a 3.0UF 330V capacitor. I haven't investigated this yet, but with four wires going into it I figure that the cap must be on the chassis somewhere. I wouldn't think that a cap problem though would cause my RPM's to drop 55RPM would it? Oh and I have no service manual, however I don't think that service manual would do me much good with this problem anyway.   > If anyone has any thoughts on this I'd sure appreciate hearing them. Thanks, Lenny   Hello everybody,   I doubt that his issue is a pinch roller no matter how badly glazed it is as his machine is running SLOW, and it the tape is being pulled ahead by the take-up torque overpowering the capstan/pinch roller, it would be running fast.   Regards, Tim Schwartz Bristol Electronics

Mook Johnson <mook@mook.net>: Dec 21 05:55PM -0600 On 12/21/2014 2:54 AM, Phil Allison wrote:   > A coin sized device made by "Epcos" that has 6 ohms cold resistance and jumps to circa 20kohms if overheated - and it can tolerate 240VAC.   > So, if the DC supply does not come up in the first 100mS, the PTC goes high and that is that. Brilliant.   > .... Phil   I believe some loudspeakers use that trick in tweeter and midrange crossovers. They called them "polyswitch" to protect them from too much continuous power.   Never used them but saw them referenced in Infinity, Polk and other consumer high'ish' end ($800+/set)loudspeakers of the 90's.

"David Farber" <farberbear.unspam@aol.com>: Dec 20 05:51PM -0800 "David K. Bryant" <dbryant_94585@earthlink.net> wrote in message news:m6itbj$1qko$1@adenine.netfront.net...   > Certainly not worth the effort and > possibly not even serviceable.   > --- news://freenews.netfront.net/ - complaints: news@netfront.net ---   Hi David,   I finally disassembled the printer again to look at the electromagnetic clutch and the related components. I put DC on the clutch terminals and manually turned the gear that the engine normally turns. I could feel the magnetic field pushing on the opposite end but the gear near the clutch did not engage. It seemed like something should have changed after energizing the clutch. Then I removed the gears and clutch from the shaft that held them. That's when I found that same type of sticky grease on the shaft that was present on the solenoids that caused a paper jam failure months ago. I cleaned the grease off with some alcohol, reinstalled the clutch and gears, and this time both gears turned when the clutch was energized with DC. I reassembled the printer and now paper processed through tray 1 works properly every time. It turned out to be an easy fix but I never would have thought to look in that area of the printer without your suggestion so thanks very much for that. (-:   -- David Farber Los Osos, CA

Jerry Peters <jerry@example.invalid>: Dec 27 09:17PM > the two bulbs in series at 40 mA input, is the resulting output > brightness going to be the same for the bulb combinations?   > 2) Which is the best method to use for preserving the longest LED life?   For 4 leds in parallel you want to *increase* the current. Assuming each led has an equal voltage drop, the current is divided among the leds, so at 10ma total, each led is getting 2.5ma. I'd go with a series configuration so you don't need a matched voltage. In a series configuration each led gets the same current with the voltage divided among them.   Since you have leds to spare, try increasing the current for a single led until it fails, this gives you an approximate upper bound on the current you can use.

Phil Allison <pallison49@gmail.com>: Dec 27 03:58PM -0800 Jerry Peters wrote:     > Since you have leds to spare, try increasing the current for a single > led until it fails, this gives you an approximate upper bound on the > current you can use.   ** IME leds do not fail in any simple way when driven with excess current.   Years ago, I repaired Mesa Boogie guitar amp that was almost new. The owner had purchased it in the USA so it ran here from a 120V step down transformer. After a few months, it developed multiple strange faults: the volume level would suddenly drop and then return, tone settings varied all over the place in a similar way and the problem got worse the longer the amp was running.   Another tech decided it must be due to bad output valves an changed the lot - for no good reason. The fault remained and then it came to me.   After verifying the owners weird story, I removed the chassis and eventually spotted something odd. The changing behaviour of the amp corresponded with varying DC voltages on the leds that were part of the many Vactec opto-couplers in this model. The Vactecs controlled tone settings and channel switching.   The 5VDC supply to the leds was quite steady so it must be faulty leds - but all 20 of them! How ?   Due to a screen printing error on the PCB, resistor positions that should have been 470ohm were installed with 47ohm parts increasing the led current to 50mA or more. The leds tolerated this for a couple of hundred hours then began to fail by dropping light output intermittently. Some would go dark and then come back minutes later, when dark the full 5V was across the led terminals.   New leds and resistors fixed it completely.   Naturally, diagnosis and repair took a fair bit of time (though leds and resistors are cheap) the owner got a substantial bill which she was quite grumpy about.   Because the amp was purchased in the USA, there was no warranty cover here in Australia. The tech who unnecessarily replaced the output valves worked for the warranty agents here in Sydney and she had paid a big bill for that work too. Her bargain priced Boogie turned out to be no bargain at all and she had to carry around a 6kg step-down tranny too.     .... Phil

mike <ham789@netzero.net>: Dec 27 06:18PM -0800 On 12/27/2014 7:28 AM, Sam Seagate wrote:   > 1) If I use either the four bulbs in parallel driven at 10 mA and/or > the two bulbs in series at 40 mA input, is the resulting output > brightness going to be the same for the bulb combinations? The brightness of each bulb is proportional to the current thru that bulb no matter what the configuration. Your numbers represent a 4:1 (or 16:1 if that's 10mA total for all 4) difference in current thru each bulb with a 2:1 difference in the number of bulbs. So, the answer is "no" but the relationships aren't entirely linear.   > 2) Which is the best method to use for preserving the longest LED life?   > Thanks in advance, > Sam The hardest part of any project is setting the objectives/specs.   My favorite system architect, Beyonce, said it best: "If you want it, put a ring on it." You need to tie down the objective. "Longest Possible" is not quantifiable and a useless constraint.   Sounds like the real objective is, make the wife happy.   Since we know zero about the LEDs, I'd assume that 17mA is a good number for reasonable life. 40mA is probably too much.   First, decide if you have 12V. If it's a regulated wall wart, you will. If it's one salvaged from a 20 year old screwdriver, it won't. Adjust the resistor to whatever it takes to get the current right.   See if there's anything you can do with tinfoil and LED positioning to aim the light where the wife wants it.   Beyond that, start adding lights at 20 mA until the wife is happy or you run out of space. With 12V, you can put up to three LEDs in series with appropriate dropping resistor to set the 20mA current. At four, I'd put two sets of two, with a separate dropping resistor for each series string. For maximum life, you probably don't want to connect LEDs directly in parallel.   Depending on the size of the lights you bought, you might find that the 27 LED's from a Harbor Freight free flashlight are smaller and can be packed in more tightly. Or you can buy unpackaged LED's dirt cheap. Just because you have Xmas lights doesn't mean that it's an optimum means to achieve your objective. Xmas lights are designed for low cost. They run for a few hundred hours and nobody worries much about whether they run at all next year. If you want high quality candles, it's better to start with high quality components.   Remember that, for most electronic stuff, reducing the temperature by 10-degrees C doubles the life. And that's the CHIP temperature, not the ROOM temperature. Chip temperature is proportional to current. If you pack stuff too tight and raise the temperature, you're defeating your purpose. While you can certainly buy single LED's that are bright enough, they're also hotter and will likely require some heat sinking. And the resistors add heat too. There is no free lunch.   If that's not enough brightness, you have to make a tradeoff. Shortening the life by increasing the current increases the wife's happiness. Anybody who has the slightest indecision about which way to go has never been married.   The lights probably came with sockets. Use the sockets and just replace them when they burn out. Spin it like a politician. Every time the light burns out, you're a hero for fixing it. Maybe you want them to fail every 28 days...be sure to get the phase right. ;-)   Bottom line is that it's not about the technology. Your tradeoffs are about the benefits of a happy wife.

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