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Point Contact Transistor Oscillator (2N110)?

I'm trying to make an oscillator circuit using an old 2N110 point contact transistor (PNP) from the 1950s. Found a few circuits on the net, but they all seem to use some forward bias and the schematics are not clear.

Connecting the device using a 1K collector load resistor and 5 volt supply causes the transistor to turn on with the base open. The transistor turns almost completely off when the base is shorted to the emitter, so it seems to work. But I can't figure out why any forward bias is needed to operate the thing in a linear mode.

I tried hooking up an oscillator circuit with a tank circuit in the collector path and a feedback winding from the inductor connected between emitter and base, so the bias would be zero, but it won't oscillate. Also tried a little negative bias with same result.

What is the easiest oscillator circuit to construct using an old point contact transistor?

-Bill

Reply to
Bill Bowden
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The emitter-base junction has to be forward biased. What you saw with it open was leakage.

Try your oscillator with a little bit of _forward_ bias; maybe a voltage divider (100k/4.7k or so, maybe even a pot during development) with the return end of the feedback winding at the junction (or the wiper), and a bypass cap from the same point to ground.

Good Luck! Rich

Reply to
Rich Grise

Yes, I tried that, but it seems the state of the transistor (leakage) is the same with forward bias or the base open. The only way I've found to shut the thing off is with a low DC resistance between the emitter and base, such as a transformer winding or 100 ohm resistor. I managed to make a low gain amplifier using a 3k collector resistor to a 9 volt supply and a 510 ohm input resistor with a 100 resistor from base to ground. The leakage is minimum with the 100 ohm resistor connected and I can switch the state of the collector with a 1.5 volt battery applied to the 510 ohm resistor. But there seems to be no current gain, only voltage and power gain. The input current that forward biases the base is about 2 mA and the collector change in current is about the same 7/3000 =3D 2.3 mA. Anyway, it works as an amplifier with 1.5 volts going in and 7 volts coming out.

-Bill

Reply to
Bill Bowden

Most early transistors were quite leaky.

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What are you looking for, all the way down here?
Reply to
Michael A. Terrell

And got leakier the older they got.

Michael

Reply to
Michael Black

Or hotter. :(

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What are you looking for, all the way down here?
Reply to
Michael A. Terrell

Just a reminder that those old transistors were germanium, not silicon, so Vbe was much lower... about 0.2V instead of

0.6V. And, as you have already discovered, they were normally on at room temperature. Were the schematics you found specifically for germaniums?

Instead of a tank-type oscillator, how about a cross-coupled flip-flop type? I seem to recall those were pretty common, at least at low frequencies.

Best regards,

Bob Masta DAQARTA v6.00 Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta

Yes, that's a possibility. I have about a dozen of these things I bought years ago and now trying to sell on ebay and give a good description. I sold one for a dollar to somebody in Australia who paid $15 for shipping. I must have spent an hour wrapping it up and standing in line at the post office to mail it and make a dollar. Then, I sold another one for $9.50 plus $3 for shipping back east. So, now I'm trying to illustrate the old transistor with a schematic so the buyer will have a good idea how it works and can duplicate my results. But I'm having trouble with Photoshop trying to show a large view of the transistor and a schematic all in the same image. My next idea is to draw a small schematic of the amplifier circuit on paper and shoot a picture of the schematic and transistor, and then touch it up with Photoshop.

Thanks,

-Bill

Reply to
Bill Bowden

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