Point Contact Transistor Oscillator (2N110)?

[Bill Bowden]

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

 

[Rich Grise]

Bill Bowden wrote:

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?

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

 

[Bill Bowden]

On Jan 5, 7:47 pm, Rich Grise <ri...@example.net.invalid> wrote:

Bill Bowden wrote:
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?

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

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 = 2.3 mA. Anyway, it works as an
amplifier with 1.5 volts going in and 7 volts coming out.

-Bill

 

[Michael A. Terrell]

Bill Bowden wrote:

On Jan 5, 7:47 pm, Rich Grise <ri...@example.net.invalid> wrote:
Bill Bowden wrote:
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?

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

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 = 2.3 mA. Anyway, it works as an
amplifier with 1.5 volts going in and 7 volts coming out.

Most early transistors were quite leaky.


--
What are you looking for, all the way down here?

 

[Michael Black]

On Fri, 7 Jan 2011, Michael A. Terrell wrote:

Bill Bowden wrote:

On Jan 5, 7:47 pm, Rich Grise <ri...@example.net.invalid> wrote:
Bill Bowden wrote:
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?

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

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 = 2.3 mA. Anyway, it works as an
amplifier with 1.5 volts going in and 7 volts coming out.


Most early transistors were quite leaky.

And got leakier the older they got.

Michael

 

[Michael A. Terrell]

Michael Black wrote:

On Fri, 7 Jan 2011, Michael A. Terrell wrote:

Bill Bowden wrote:

On Jan 5, 7:47 pm, Rich Grise <ri...@example.net.invalid> wrote:
Bill Bowden wrote:
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?

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

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 = 2.3 mA. Anyway, it works as an
amplifier with 1.5 volts going in and 7 volts coming out.


Most early transistors were quite leaky.

And got leakier the older they got.

Michael

Or hotter.


--
What are you looking for, all the way down here?

 

[Bob Masta]

On Wed, 5 Jan 2011 19:36:30 -0800 (PST), Bill Bowden
<bperryb@bowdenshobbycircuits.info> wrote:

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

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
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
Science with your sound card!

 

[Bill Bowden]

On Jan 8, 4:48 am, N0S...@daqarta.com (Bob Masta) wrote:

On Wed, 5 Jan 2011 19:36:30 -0800 (PST), Bill Bowden



bper...@bowdenshobbycircuits.info> wrote:
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

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
             www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
    Frequency Counter, FREE Signal Generator
           Pitch Track, Pitch-to-MIDI
          Science with your sound card!

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