Tag Archives: 2n5160

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Motorola 2N5160 PNP RF Transistors: new-old-stock, medium old stock, fake stock?

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Some of the 1980s, 1990s pulse and signal generators use push-pull power amp stages to provide output levels of +-10 V into 50 Ohms, and similar. These are often discrete circuits, utilizing PNP-NPN small power transistors. While the NPN types are still widely available, there used to be some shortages of 2N5160 PNP transistors. Recently, there are are many offers for “Motorola” branded parts, with datecodes from about 1998 (K98xx) to about 2004 (K04xx). In contrast to the earlier Motorola parts (Rxxxx date codes), these have shiny cases. It is quite unlikely that Motorola actually manufactured RF metal can transistors in 2004… (1999 onwards, Motorola no longer made transistors, but transferred the business to ON Semiconductors).

Strangely, the cans have “KOREAN” stamped into them, in various styles and sizes. Would a fake producer have stock of many different kinds of fake cans? Or did ON Semi produce these parts with some existing stock from the 1990s? Many semiconductor producers actually have decade old wafers in stock that they package whenever there is a need.

Let’s have a closer study. Unfortunately, no electron microscope here. But we do our best. Here the die of the defective HP branded original Motorola part. Red arrow shows the burn mark, defect area.

I sacrificed one of the 0.7 USD suspicious parts with K0439 datecode. To my great surprise, they are exactly identical in die, bonding method, and die attachment method.

A quick function test – put the new K0439 date code 2N5190 into an 5 MHz power amplifier. And working just great at >20 dB gain and about 1 Watt output.

Further, we study the collector-base capacitance, at -28 Volts bias U_CB (note that some datasheets specify “28 Volts U_CB” but this won’t work with a PNP transistor – it is conducting like a diode in C-B, if the collector is positive vs. base).

A test with the trusty HP 4192A, and 2.5 pF measures. Exactly the typical value. Also checked one of the certainly genuine Rxxxx date code transistors, and this measured at about 2.7 pF.

Test done at 1 MHz, and calibrated the 4192A with open and short.

So far, so good. All I can say is that these transistors are good 2N5160, whoever made them.

Various

HP 3325B Synthesizer/Function Generator: a quick fix, and a hot transistor

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Recently, I got a defective HP 3325B, it is a very useful generator even for today’s standard. It features some highly linear ramps, has great frequency resolution and a powerful output (10 Volts p-p into 50 Ohm). This unit reportedly had major issues, no output, and failures with startup. So even before switching it on, I removed the panels to check. Nothing obvious at first glance.

After a quick power on, some smell from the output section, and clearly, there are some burned resistors, and one of the power stage transistor is terribly hot, so hot that the solder melts… don’t burn you fingers!

Removed the board altogether (take care not to damage the connection flat cables!), and even the solder had some spray by heat effect, so I cleaned the area well.

To get access to the resistors, and to also do a proper test, all the transistors in the area were removed, and the transistors desoldered. All cleaned up pretty well, the board seems to be of good quality.

The 3-440 transistor aka 1853-0440, cut open. It has a tiny chip, difficult to see the damage with my means, but it is shorted to base.

The resistors, the only issue is a slightly discolored 47 Ohms carbon composition resistor, part EB4701, a 0.5, 10% tolerance resistor. Quite expensive to get, and the part, despite some signs of heat, tested good and within tolerance. So I decided not to replace this transistor, because it has an effect on the high frequency performance of the circuit.

The power amp, it is a marvelous push-pull design. It relies on complimentary NPN-PNP transistors that have high frequency power.

Nowadays, the PNP RF transistors of this sort are rare, probably they even were rare and expensive during their time.

The damaged resistors, fortunately, after a good amount of searching, I found the bags here in by temporary Japanese workshop.

The transistors, these 3-440 are equivalent to the 2N5160, and I happened to have 3 of these back in Germany, new old stock. Purchased them some years back, because they are generally not easy to get.

After these replacements, I run the adjustments and performance checks as per service manual, with no trouble at all. Also the self test passes flawlessly. We can call the generator fixed.

Out of curiosity, I checked with ebay, and there are very reasonable offers of what appear to be Chinese copies of 2N5160 transistors. They have the Motorola label, but to my knowledge, the date code is much past the obsolescence of these parts at Motorola. So I am waiting to receive these parts, and will give them a good test and study, to see if these are good replacements, or just fake.