OC170 transistor with three leads.

[Station X]

I've come across an OC170 with only three leads instead of the usual four. Yes I have checked that the screen lead hasn't been cut off, but this is definitely a three lead transistor. It's marked OC170 with 328 below that.

It's in what looks like a T05 case with the leads arranged in a triangle. Diode testing the junctions shows that the lead at the apex of the triangle is obviously the base. The question is which leads are the collector and emitter?

I'm assuming an L01 layout which makes the lead nearest the tab the emitter. It would be nice to know for sure though.

Does anyone know the answer?

Thanks.

[gezza123]

hi.graham.according to my mullard data 1970.it is a TO-7 case,

Germanium pnp alloy junction transistor for use in f.m receivers.

construction TO-7
vcb MAX (IE=0
ICM max 10 mA
Ptot max (Tamb=45'c 50 mW
pOWER GAIN (f=10 MHz) Typ. 25 db
ICBO(VCB=-6V: IE=0)Typ. 1.2 uA
hfe (VCE=-6V IE-1mA Typ. 150
4 pin device
pins = left to right e.b.s=internal shield and metal case +colector

hope this helps Gezza

[gezza123]

Seems odd to have delta pins.
hereis my docs.Gezza

[Sideband]

I bet it's a remarked transistor. I have an odd AC127 which is very much thinner than a standard type...definately not made by Mullard. Your's may be a similar equivalent 'replacement' type.

Just speculating


SB

[TrevorG3VLF]

Try a 100k resistor from collector to base and measure resistance between emitter and collector with an analogue meter, get them the right way round and you will get gain and low resistance. The leads are likely to be the wrong way round i.e. red negative. I have never seen a C,B,E transistor in a can.

[neon indicator]

if you have an hfe tester the gain is always lower in reverse than correct way round. With Ge the reverse gain is closer to normal gain than with Si it's 10:1 to 50:1 ratio

[Philips210]

I have just built a very useful RF Transistor Tester from the American CQ magazine (May 1975) and I find it particularly useful. If the C and E leads are transposed then the dynamic gain is much lower than with the correct C E placement.

Symon.

[Station X]

A bit more info. This is fitted in a Codar T28 Receiver and has obviously been there from day one. The PCB pad marked "S" for screen is completely devoid of solder. Yes I know this is a carp receiver, so there's no need to remind me!

Finding that the voltage readings round the OC170 were all wrong I removed it thinking that I'd have to replace it with an AF127. I then found that one of the resistors in the potential divider on the base had changed in value from 10K to 2K, so I changed the resistor and got the voltages I'd expect with no transistor fitted.

Turning my attention back to the transistor I observed that it was a three lead device in a T05 case. Both junctions tested OK on a diode test with a volt drop of about 0.2V which points to the device being germanium rather than silicon. There were no shorts from any of the leads to the case. As you've guessed I'd forgotten the orientation of this component prior to removal.

Using the hfe test of my DMM showed zero when connected one way and about 120 when connected the other. This confirmed that the tag on the case was nearest the emitter. The transistor was replaced in the circuit and the voltage readings looked much better.

Interestingly this site shows the OC170 as being a three lead device:-

http://vintageradio.me.uk/info/germanium.htm

[oldticktock]

Some additional data you might like.

Chris

[Station X]

Thanks to everyone who posted data or links to it. What I'm really interested in though is any info relating to the three lead version. It probably dates from 1968.

Here's the best picture I could manage. It just about shows the trangular lead formation.

[murphyv310]

I have a couple of that type of OC170 as well as the normal 4 legged devices!

[KeithsTV]

I suspect that transistor is not made by Mullard and would probably not suffer from the tin whisker problem that afflicts the TO7 canned types.

Keith

[gezza123]

Here is some more data Gezza

OC170 are Germanium PNP transistors in a TO1 type package
for use as a medium power amplifier.

Absolute Maximum Ratings: (TA = +25°C unless otherwise specified)
Collector?Base Voltage, VCBO. . . . . . . . . . . . . . . . . . . . . . . . . . . 32V
Collector?Emitter Voltage (RBE = 68?), VCER . . . . . . . . . . . . . . . .10V
Collector Current, IC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1A
Total Device Dissipation (TC = +25°C), PD . . . . . . . . . . . . . . . 650mW
Operating Junction Temperature, Tj . . . . . . . . . . . . . . ?55° to + 90°C
Storage Temperature Range, Tstg.. . . . . . . . . . . . . . . ?50° to + 90°C

[murphyv310]

The above doesn't look correct for an OC170! I will compare it to my Mullard Maintenance manual later.

[Station X]

Originally Posted by KeithsTV

I suspect that transistor is not made by Mullard and would probably not suffer from the tin whisker problem that afflicts the TO7 canned types.

The example I have definitely doesn't have the tin whisker problem. Even if it did it wouldn't matter, as the can isn't grounded due to lack of a fourth lead. However I understand that whiskers can grow from more than one lead to the can, or between leads.

[neon indicator]

Originally Posted by murphyv310

The above doesn't look correct for an OC170! I will compare it to my Mullard Maintenance manual later.

Quite!

10mA IcMax and 80mW

According to the PDF attached. Which sounds more believable.

[Station X]

The same Codar T28 Receiver is supposed to have an AC155 fitted in the BFO and operating on 505 KHz. However in my receiver an ACY40 is fitted and it looks like it's been there from day one.

The ACY40 has a full short from the base lead to the case which I don't think should be there. However the voltages look OK and the BFO operates correctly. For that reason I'll leave it alone and won't attempt to blow away the tin whisker, if that's what it is.

Next step is to change the AF117s in the LP1156 IF Module.

[jimmc101]

Originally Posted by Station X

...The ACY40 has a full short from the base lead to the case which I don't think should be there....

I suspect that this is as it should be, my 1964 'General Electric Transistor Manual' lists all of the Germanium Alloy transistors in the TO5 case as having the base lead internally connected to header.

Jim

Just found a copy of a different edition online http://babel.hathitrust.org/cgi/pt?u...31924004608539 Outline 2

[Station X]

Thanks for that. It's a good job I didn't attempt to blow away the short.

[ronbryan]

I think the first transistor in the LP1156 is actually an AF115. I never understood why Mullard loaded higher spec transistors in parts of their modules, compared to an equivalent non-module radio. Maybe the test spec was onerous.

Ron