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2018-12-18 Al And Trudy

from another blog on blogspot 2011-08-013

Saturday, August 13, 2011

Al And Trudy

Al and Trudy – Aug 13, 2011

Back in the ’70s, I rented an apartment to an older gentleman who said he was a minister, and his wife. I remember her name was Trudy, and I’m somewhat sure his name was Al.

Al and his wife minded their own business; I didn’t see them much. One day, I was working outside and Trudy asked me if I would like a dish of strawberries with whipped cream; well, I couldn’t turn that down. I sat down and she brought a dish out of the fridge, grabbed a spoon, and gave them to me. I dug in, but the very first bite tasted moldy. She was surprised when I said so, and tasted a bit, then she felt bad about it and apologized. I thanked her anyway.

A few months later, I noticed that I had seen Al around but not Trudy. I asked why, and Al told me that she had become depressed, and had to be hospitalized. After that, I never did see her again, but Al continued to live there for more than a year, maybe several years.

One day, Al knocked on my door and asked me if I knew anything about car ignitions. Being an electronic technician, I said yes. He told me he had put an ignition kit on his car and now it wasn’t running right. We went out and he showed me that it would start, but the old Chrysler V8 would cough and sputter if he put his foot on the gas pedal.

This was a big old ’60s Chrysler, with the big V8 engine. He had installed new points, plugs and condenser (capacitor), and they looked okay; he had done this before and knew what he was doing. I asked him if he had tried putting the old ones back in. He said no, because these were brand new. Well, that doesn’t mean the parts are not defective, I told him.

With the distributor cap off, I looked at the points but saw nothing unusual, I pulled the high voltage wire out of the middle of the cap and grounded it, and asked him to try to start the engine. I could see that the points were opening and closing, so they were adjusted somewhat okay. I put the high voltage wire back into the distributor and asked him to try the old condenser. He got the old one, put it back in and made sure everything else was okay, and put the distributor cap back on.

He got in, started it up, and stepped on the gas. VROOM! VROOM! The old V8 was running great. Al thanked me and said that he couldn’t understand why that brand new condenser was bad. I had no clue at that time, either, but I told him that condensers don’t usually go bad, and the old one would probably work okay until he needed to change the points again.

Later in life, after my own experiences with defective merchandise, I learned from the school of hard knocks that stores are often the victims of an insidious problem, but often contribute to the damage. Customers damage the goods, or pull out the good item and put a damaged one back in the package, and take it back to the store for a refund. The store restocks the item (they have a shrink wrap machine in the back so it looks just like it’s new from the factory). I buy the same item and end up with a lemon. And if I return it, it most likely will end up on the shelf again, and someone else will end up getting the same lemon.

I got a lemon from m Fry’s when I bought a ‘build your own’ computer. The CPU was dead, so I took it all back and got my 600 dollars refunded. For this reason, and also because many of Fry’s sale items have rebates (which have cheated me more than once), I no longer buy computer stuff from Fry’s. I have had much better results buying from online stores.

However I have had several bad experiences online when buying from sellers on eBay. In the summer and fall of 2010 I blogged my bad experiences when buying camera lenses on ebay. Prior to that I had several more bad eBay experiences, mostly with power supplies and test equipment. But eBay sellers may be victims of and contributors to the same subterfuge.

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2018-12-17 Radio Shack P-Box Kits

from FB group Building Transistor Radios 2018-12-17

Seems that what you’re saying is these P-box kits were very slow sellers, so they ended up as overstock at the surplus store. What I find odd is that I used to buy parts from RS but I can’t remember ever seeing these kits in the store. I remember the science fair kits, though. But I wasn’t interested in RS kits, I went to Heathkit and bought most of my kits, or bought the ones I saw in the electronics magazines.

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2018-12-14 Voice Filter For Telecom And Radio Comm

from FB group Building Transistor Radios 2018-12-14

A voice band filter for telecomm or radio comm. The .068 or .0068 uF caps can be made by putting a 0.1 and 0.22 or .01 and .022 uF capacitors in series. The opamp can be a 1458 ‘dual 741’ opamp.

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2018-12-12 LM78xx Linear Regulator Disadvantages

from FB group Building Transistor Radios 2018-12-13

Joseph Rotello
I agree with some of your claims. But I know far more about 3-terminal regulators than you think. First off, your claim that they are more efficient is unproveable. There are linear PSes that are more efficient. That was the reason LDO regulators were used. You claim they have far better regulation, but a few simple Opamps can do equal or better. I agree “they cost less to create.”

But you claim “they offer greater reliability” is simply not true. The built-in thermal shutdown ‘feature’ causes them to go into voltage brownout mode when they overheat. Suddenly the 5V output drops below 4.75V and the circuits the regulator is supplying start to have problems and errors. And don’t try to weasel your way out of this. The company I worked for had to send one of its repairmen overseas to replace 7805 regulators that were overheating and causing the microprocessors to get errors.

One thing you can’t do with 3-terminal regulators is get very good regulation. With a discrete design the sense leads can be run from the power supply through a four wire cable to the equipment, and the voltage will be precisely regulated at the equipment, with compensation for the IR drops in the cable.

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2018-12-09 Selectivity V. Sensitivity

from FB group Building Transistor Radios 2016 Dec 9

Jim Glover
An ideal receiver would have a bandpass shaped like a square wave where the bandpass is flat with no attenuation and the attenuation is infinite outside of the passband. In the real world this isn’t possible but any receiver buyer with the money would pay more to get a receiver that approaches the ideal. So I don’t see a necessity to compromise one for the other. For AM BCB the sensitivity is not as important because the atmospheric background noise is high and making a receiver more sensitive just gives more atmospheric background noise.

This higher selectivity is the reason why the superheterodyne receivers with IF stages are so popular. Superhets replaced Regenerative receivers when the costs of vacuum tubes came down. Selectivity is the reason why there are more than a single IF can in a decent receiver and why the receivers added ceramic filters. Good selectivity adds greatly to a good receiver.

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2018 Dec 8 Sinclair Book 22 Tested Circuits Using Micro Alloy Transistors

from FB group Building Transistor Radios 2018 Dec 8

Nick Bastian posted the schematic of a Sinclair Micromatic radio. I found the book by Clive Sinclair about the circuits using micro alloy transistors. Germanium transistors and especially micro alloy transistors are no longer made so it’s better to use silicon BJTs instead. Here is the link and the cover and first page.

http://www.americanradiohistory.com/Archive-Bookshelf/Author-Groups/Clive-Sinclair/22-Tested-Circuits-Bernard-181-Clive-Sinclair.pdf

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2018-12-04 FETs For Very Low Voltage Joule Thiefs

from FB group Building Transistor Radios 2018 Dec 4

Terry Harris
I didn’t try to mimic the ALD, I used the FETs for a voltage booster. The typical 5mm LED needs somewhere around 60 mW for Max brightness. If I was powering it with 60 millivolts, it would require over an amp to get the LED lit brightly. Since FETs might max out at a few tens of milliamps, there needed to be several in parallel. You have to remember that JFETs are already conducting with zero gate voltage, so they will oscillate with tens of millivolts supply voltage if the feedback winding is high enough turns ratio. Once the supply voltage gets below a volt, things that were once minor suddenly dominate the performance. Resistances of a small fraction of an ohm can cause a major drop in performance.

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2018-12-03 My Fluke 75 DMM

from FB group Building Transistor Radios

Joe Lima
That’s good to hear. More than a year after I bought my Fluke 75 DMM (and with light use at home) I turned the switch to off but it stayed on(!!) I had to unplug the battery. Luckily it was still under the 3 year warranty, so I sent it to Fluke to get it repaired and got it back fixed, calibrated, etc. I had used Fluke test equipment before that and I had a lot of faith in Fluke reliability, but my DMM failure destroyed a lot of that faith. The next DMM I bought was a B&K, and it has performed flawlessly for more than a decade.

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2018-12-02 How to Determine If Diodes Are Real Germanium

From comment left for Roger Kainka Labs video on YouTube

Another 100% accurate method of determining if it’s germanium is how sensitive the device is to changes in temperature. The leakage current of germanium is much more sensitive to temperature changes than silicon.

What angers me is that some circuits are designed with depending on the germanium diode’s leakage current to function. Some detector diodes charge a DC blocking capacitor and discharge the blocking capacitor through the diode’s leakage. These seem to be the problem circuits if low leakage Schottky diodes are used. It seems to me that a high value resistor to simulate the leakage would help the Schottky diode to work like the true gernamium diodes. I am speaking about detectors not used in crystal sets. The crystal sets may not work with a resistor because the resistor has a linear V-I characteristic, and the germanium’s leakage does not.

One thing that might help is to put many of the ‘fake germanium’ Schottky diodes in parallel to increase the leakage current. The fake diodes are so much cheaper than real germanium that a dozen or more of them could be paralleled. Or high current Schottky diode like the 1N5817 could be used to get high leakage current.

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2018-12-02 How to Determine If Diodes Are Real Germanium

From comment left for Roger Kainka Labs video on YouTube

Another 100% accurate method of determining if it’s germanium is how sensitive the device is to changes in temperature. The leakage current of germanium is much more sensitive to temperature changes than silicon.

What angers me is that some circuits are designed with depending on the germanium diode’s leakage current to function. Some detector diodes charge a DC blocking capacitor and discharge the blocking capacitor through the diode’s leakage. These seem to be the problem circuits if low leakage Schottky diodes are used. It seems to me that a high value resistor to simulate the leakage would help the Schottky diode to work like the true gernamium diodes. I am speaking about detectors not used in crystal sets. The crystal sets may not work with a resistor because the resistor has a linear V-I characteristic, and the germanium’s leakage does not.

One thing that might help is to put many of the ‘fake germanium’ Schottky diodes in parallel to increase the leakage current. The fake diodes are so much cheaper than real germanium that a dozen or more of them could be paralleled. Or high current Schottky diode like the 1N5817 could be used to get high leakage current.

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