Archive for February, 2019:

2019-02-26 BF199 Half Price Offer Accepted

I made an offer for a lot of BF199 transistors on eBay, and got it. They wanted $9.90 for 200, so I offered $5.00 and they accepted my offer. That works out to 2.5 cents per transistor, not including shipping. There was only a single photo and the transistor in the photo was labeled PH

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2019-02-20 Old 2N708 Transistors

Feb 20 I got 21 ‘packages’ of 2N708 transistors for $.99 a package from Goldmine-elec.com. In the box were 42 plastic zip bags, each having 5 2N708 transistors, so apparently one ‘package is two bags. Each transistor is marked with the Motorola logo and 2N708 and on the top KOREA is stamped into the metal.

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2019-02-19 Transistor Tester & Running From Single AA Cell

from FB group Building transistor radios 2019 Feb 19 I use a wall wart on mine. It’s a 6VDC regulated output. The tester says battery is low (it expects 7 to 9V) but it still works okay. I have a few of these, it uses a microcontroller. Notice that it runs using a single AA

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2019-02-16 The Old Time Rejected Components Cartel

Left link to this on FB. I saw the Electronic Goldmine email ‘flyer’ ad for 2N708 transistors on sale so I had to order a bunch of those to experiment with. But their ad said nothing about them being NOS (new old stock). I’ve bought some junk from them before that were rejects or floor

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2019-02-12 FM Microphone Schematic and Parts Placement

I got three of these no name, unbranded kits from a seller on eBay. The kit comes with all parts and a PC board, but the labels on the board are R1, R2, R3… but no values for the parts. There is a schematic and photo of the completed board, but the schematic has no

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2019-02-11 The College IT Datacomm System

from FB group Bell Telephone… 2018-02-12 After the early ’80s when the RBOCs created the MPOE, all their wiring on campus became ours, and we never got any records from them of what was in the ground. On top of that we had a contractor come and install gel filled telephone cable along with ITV

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2019-02-10 Parallel Resistors Made Easy

Something that should be memorized by every technician. This also applies to capacitors in series.

2019-02-09 AA5 OPTs And Winding

from FB group Building transistor radios All the AA5 single ended OPTs I’ve taken apart have had the ‘air gap’ which is really a piece of paper. I presume that is because the DC current magnetized the core and if it didn’t have the gap it would saturate and have a lot of distortion. I

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2019-02-08 Solenoid Used To Switch a Toggle Switch

from FB group Building transistor radios Feb 11 Cool! I found one circuit that used a neat trick. They put a large value electrolytic in series with the coil, and a low value power resistor across the capacitor. When the coil is energized the full current goes through the coil until the capacitor is charged,

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2019-02-05 Floating Detector Diodes Are Not A Good Design.

from FB group Building Transistor Radios 2019-02-05 Graeme Heal Aaron Cake has a lot of good circuits and projects. But this one uses the ‘floating detector diode’ with no DC return path, so the circuit will only work if the diode’s leakage current provides the discharge. That means the diode must be germanium, not silicon,

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