What Germanium PNP transistor do I use?

Old rule: As long as Ge was only one cent less than Si, they'd use Ge. Maybe the fact that many cars were still equipped with 6V systems also favored Ge.

--
Regards, Joerg

http://www.analogconsultants.com

As a kid I always laughed when I saw yet another circuit proposal with a tunnel diode or a UJT. None of the stores had any, not even the big ones in large cities. Looked like someone just had to publish it to show off. I built my oscillators with scavenged AF139/239. Or sometimes tubes.

Most of what people thinks is fresh production is in reality just old stock. When it's gone it's gone, plus they often want top Dollar.

--
Regards, Joerg

http://www.analogconsultants.com

The 12V auto-electrics were well and truly established in the period I remember, and don't forget the first ever transistor radio used a 22-1/2V (tube) hearing aid battery - presumably the PP3 hadn't been invented yet.

A few years ago I had a project published in Television Magazine which was loosely based on a Programmable Unijunction Transistor (PUT).

The project met the need for testing opto-couplers that did not offer an electrical connection to the photo-transistor's base terminal making the usual "diode" tests impossible, this required a cheap simple and minimum parts count pulse generator to drive the LED, granted regular UJTs are very rare these days so initially I looked at the PUT which is basically a thyristor with a negative (anode end) gate, my first thought is that an SCS (silicon controlled switch) - a 4-layer thyristor device with both gates available would be relatively easy for a TV engineer to obtain, and failing that, one can be constructed easily with a complementary pair of small signal transistors.

However as I looked at the circuit - and the complementary asymmetry of the

4-layer device, I realised that it was possible to turn the circuit upside down and use a small TO-92 thyristor to the same effect. Thyristors of this type are quite common in TV & monitor PSUs - not least as safety trip devices, so almost by accident the project became a dual purpose component tester.

Don't be too hasty to count out the tunnel diode - according the manual, the Tek465 scope contains a couple of them.

Apparently, they're available _SOME_where - at least the audiophools seem to think so:

(although, a glance at the price tag kinda makes me think they've set up their own custom fab line or something ;-) )

Are schottkys not good enough?

Cheers! Rich

At the time, Ge was the only way that they could make cost-effective power PNPs. They still had some bugs to work out with making high-power Si PNPs. (they've apparently figured it out sometime in the last 30 years or so, however. ;-) )

Hope This Helps! Rich

I thought that was due to the curve of a new device. Transistors started out as being good for not much more than audio, and low power at that. They worked at it, until there were better frequency capability and they could actually build audio output amplifiers out of the transistors. Witness all those hybrid radios (not just car, but there were early lunchbox style walkie talkies that were hybrid), where the audio stages were transistorized and maybe some of the lower frequency stages, while tubes remained in most of the radio stages.

Silicon came along, and they had to start all over, working at improving their frequency range and power capability (though likely the curve wasn't as slow since they'd practiced on germanium). By then, they could make fully transistorized radios, but not always with silicon.

Look at the early transistor audio amplifiers, and they were basically copies of tube amplifiers, ie transformer or RC coupled, with an output transformer. A few years later, they were DC coupled, and depending on the design may not have even had a coupling capacitor at the output.

Michael

In the period I'm thinking of transformer coupled O/P stages still hadn't been completely outdated by complementary pairs so they could have chosen whichever polarity suited best - it just seemed to take a while to develop silicon transistors that could supersede germanium in power stages.

But that was one of the exceptions. IN the hobby realm, they were a novelty and nothing that was published could not be done with some other device.

In that scope, it's either in the trigger system, or it's generating a pulse (I forget, though I know at some point I did read what the tunnel diode was doing).

ANd yes, if you needed to replace that tunnel diode, you'd need a tunnel diode. But, even for that, there seems to be a fair consensus that getting a tunnel diode at this point would require effort at the very least.

Michael

There may have even been some chasm to leap to NPN. So many of the early circuits did use PNP transistors that one might suspect there was some problem in making NPN. But perhaps it was just lethargy, they started out with PNP and kept with them up to a certain point. Or those positive ground cars made PNP a better choice at the time.

Michael

Then you must be young. My first car was built in 1969 (I got it around

1980). A Citroen 2CV, 6V electrics all through out. Number of electronic components in that car before installing the radio with its Ge transistors: Zilch. Not even a diode.

--
Regards, Joerg

http://www.analogconsultants.com

Effort plus a well padded bank account. Unless you can find a similar scope with a shot CRT on EBay for parts. But then shipping will eat your money.

--
Regards, Joerg

http://www.analogconsultants.com

I needed something similar at a client. At my lab I have one, a plain old pencil shaped signal injector. But new TSA rules consider that a dangerous items. So.... I made sure the client had some CMOS logic at hand. Took a single Schmitt inverter (but a 74HC14 would also have sufficed), one resistor, one cap and bingo, I had a new pulser.

In their haydays those big scopes fell into the category "money is not an objective" :-)

--
Regards, Joerg

http://www.analogconsultants.com

Call that a car - its French FFS!

Maybe I got the number wrong - its not one of those big "double decker bus" scopes you wheel about on a trolley.

Don't know what FFS means but that was a great car. 16 horses, about

50mpg on regular unleaded and transported a huge fridge that a guy couldn't get into his VW bus. He was pretty embarrassed.

Heck, I could even adjust the shock absorber strengths on it with getting dirty.

--
Regards, Joerg

http://www.analogconsultants.com

16 HP? My dad's lawn mower is 18 HP.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

US cars were 12 volts a lot earlier than that. My '61 Ford Galaxy was

12 VDC. I could dig through my collection of Sams Photofact car radio manuals to find the exact dates, but 12 VDC was in wide use when car radios were still using vacuum tubes in the US.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

US car radio audio output transistors went from PNP Germanium to NPN Silicon in one step. The first I saw was the Bendix with the early TO-220 where they bent the leads right at the body to fit the spacing on a TO-3 transistor and had an almost 100% field failure rate within a year.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida