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2018-08-27

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on August 27th, 2018 by - No Comments

From FB group Building Transistor Radios 2018-08-27

Michael Kronsteiner
I would say that germanium transistors could not handle “high” currents because the designers were unwilling to use anything more than the cheapest germanium transistors that could barely do the job. In the 1960s there was the Workman “99 Power” that was in the TO-3 diamond metal case and sold for 99 cents. This was a popular replacement transistor. There were the AD161 and AD162 and the 2SB492 germanium transistors in the TO-66 or similar package but the makers were too cheap to use them. These could handle much higher current safely compared to the cheap output transistors on most consumer electronics.

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2018-08-24 2N3904 & 2N3906 for Output Transistors

Amplifier Audio Transistors
on August 24th, 2018 by - No Comments

From FB group Building Transistor Radios 2018-08-24 – The discussion was about the OTL complementary symmetry audio amplifier that Mr. Barnett has posted several times to the group, which uses a 2N3904 and 2N3906.

Willie Barnett
Let’s talk about current. Suppose your amp has a 9V supply. When the output transistor is turned fully on, the peak current can be as much as 1 amp through the 8 ohm load. The absolute maximum rating for the 2N3904 or ‘6 is 0.2 amps. So the peak current is *five times* the absolute maximum rating for those transistors. Now do you understand why I have said that you should not use the 2N3904, 2N3906 or the BC547 or BC 557. These small signal transistors will go into thermal runaway. If they don’t, you’re just lucky.

The better choice is to use the PN2222A / PN2907A or the BC337 / BC327 or the C8050 / C8550. These were made for this amplifier.

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2018-08-22 “Crooked Donald” Trump

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on August 22nd, 2018 by - No Comments

Quoted from end of this article

https://www.theatlantic.com/amp/article/568147/

“Whatever legal and political consequences ensue, Trump voters should know that they cast their ballot for a man who has lied to them all along, even about a felony that would help him win the 2016 election. A nickname that pithily distilled his behavior would be “Crooked Donald.” America cannot be great again so long as he corrupts its presidency, poisons its discourse with lies, shows disregard for the authority of its laws, and sets an example of mendacious debasement for its children.“

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2018-08-20 2N3904s From Mouser And Ebay

Measurement, environment Transistors
on August 20th, 2018 by - No Comments

from FB group Building Transistor Radios 2018-08-22

Olek Kopyto
I recently did some tests on 2N3904s I got from Mouser and from a Chinese eBay seller. The ones from Mouser had a current gain of right around 200, right in the middle of the 100 to 300 gain range according to the data sheet. The Chinese were all 300 or more, some as high as 390. This is out of range, and it doesn’t seem to be as bad as if it was too low. But if a circuit is designed for below 300, using one with higher than 300 could cause stability issues such as oscillation or instability.

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2018-08-18 Two Types Of Germaniums In Old Radios

AM Band Radio, Television entertainment Repair, alignment
on August 18th, 2018 by - No Comments

From FB group Vintage Transistor Radios

There are really only two types of germanium transistors in older radios. One is for the RF and IF stages and has low collector to base capacitance. The other is audio and can handle a few hundred milliwatts. I recently replaced the germanium audio transistors with silicon, with change to the base bias resistor.

The old radios I’ve troubleshot have seldom had problems with the transistors. Mostly problems with electrolytic capacitors drying out, and carbon composition resistors changing to a much higher value. Before you remove a transistor (and risk damaging it), check the capacitors and resistors.

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2018-08-16 Cancer Loves Fat Cells

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on August 16th, 2018 by - No Comments

Sci Am article

https://www.scientificamerican.com/custom-media/cancers-hidden-helper-your-fat/?utm_medium=Display&utm_source=1865911&utm_term=226398931&utm_content=101129235&utm_campaign=20582999

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2018-08-03 GE Special Speaker And Iron Particles

Mechanical devices Meters and Test Equipment
on August 3rd, 2018 by - No Comments

From FB group Building Transistor Radios, Aug 6

This also happens with the meter movements of old analog meters. The iron particles get into the magnet assembly and stop the coil from moving. The only way I’ve found that gets rid of the iron particles is to very gently put a thin piece of steel into the gap and get the particles to stick to it then pull it out. This may have to be one particle at a time, and may take a long time with many particles. You can’t use a magnet because that can demagnetize the speaker magnet. A nonmagnetic tweezers is helpful. One thing I haven’t tried is adhesive tape. But tape could damage a meter movement. A speaker might be less delicate and the tape might remove many particles at a time.

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2018-08-01 Almost Electrocuted by HV

Electrical System Health
on August 1st, 2018 by - No Comments

From FB group Bell Telephone… Aug 1

We got to move into our new computer center bldg in ’96, and the old bldg was being demolished. Two guys were jack hammering in a ditch when I drove by going to another site. When I came back later, they were gone but all the equipment was still in the ditch.

Turned out they were cutting into concrete in the trench, and they broke through. Well, this was red colored concrete that identified it as high voltage underground cables, 4 kV at hundreds of amps. When they punctured through the cable, it went off with a huge arcing fireworks, and luckily for us, it ended with the cable going open, not shorted. Scared the hell out of the workers, and they were lucky they didn’t get electrocuted! IIRC, they run red warning tape over the conduit in the dirt. Apparently these fools were never trained on any of that, and it could’ve cost them their lives! 😱

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2018-07-30 How Are LED Lights Made Dimmable?

LED LEDs Lighting
on July 30th, 2018 by - No Comments

From FB comment to Bill Sherman’s candelabra lamps.

Bill Sherman
Sometimes I wonder what is meant by dimmable. If a LED light uses hundreds of microfarads for the DC filter capacitor, then when the light is dimmed, the long time constant causes it to flash on and off when it is dimmed. So if the filter capacitor is much smaller, the flashes get much faster until they are too fast for the eye to see. Then the light doesn’t “act weird” when it is dimmed. So is this all that is done to make a LED light dimmable? 😮😮

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2018-08-29 High Temperature And Nylon Screws

Building projects and kits Do It Yourself Electromechanical Mechanical devices Repair, alignment Transistors
on July 29th, 2018 by - No Comments

From FB group Hobby Electronics, 2018-09-01

I faced this dilemma before. I’ve repaired power supplies where the transistor failed because it was not held tightly to the heat sink because of a nylon screw that got hot. I used a steel screw and a fiber washer, and heat shrink tubing over the threads to insulate. Another way is to use mica washers which will not yield under heat.

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