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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 2nd Feb 2016, 1:07 pm   #1
Station X
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Default What are these devices?

Sorting through my component stocks I found two devices in T-05 two lead cans. Printed on them is:-

78 (Unidentified Manufacturer's Symbol?) 28
T484
BRITAIN

Anyone know what they are?

Thanks.
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Old 2nd Feb 2016, 1:55 pm   #2
turretslug
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Default Re: What are these devices?

Do they have a thick central lead surrounded by insulating epoxy and a peripheral lead welded to the can? There are a few veteran HP things here that have rectifiers answering to this physical description, can't remember the type numbers though.
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Old 2nd Feb 2016, 3:08 pm   #3
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Default Re: What are these devices?

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Originally Posted by turretslug View Post
Do they have a thick central lead surrounded by insulating epoxy and a peripheral lead welded to the can?
No. They look like a T-05 transistor or regulator. I did a diode test on one and it tested like a transistor.

I'll try to photograph the logo later.
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Old 2nd Feb 2016, 3:14 pm   #4
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Default Re: What are these devices?

Sorry. It's a TO-3 can.
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Old 2nd Feb 2016, 6:00 pm   #5
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Default Re: What are these devices?

Try it as a transistor at fairly low power and see if it works.

Collector'll be the can, base'll be the leg that both the can and the other leg "diode" to.


Usually

.................O
.....................
.............B.......E


.................O

(Imagine the lozenge outline in this bottom view.
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Old 2nd Feb 2016, 6:28 pm   #6
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Default Re: What are these devices?

78[x]28 in a TO-3 can would make me think of a 28-volt regulator! Though that's an odd voltage (usually they were 7805, 7812, 7815 or 7824: I do vaguelly recall a 7828 being custom-specified in some aviation gear though).

What is the [x] logo? Post a photo and I may be able to dig up a memory of it from my 1970s/80s strange-semiconductors memory.
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Old 2nd Feb 2016, 6:34 pm   #7
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Default Re: What are these devices?

My initial thought was a 28V regulator, but I couldn't find a data sheet for a 7828. On a diode test it tests like a transistor. Would a VR do that?

Tried to photograph it under artificial light, but it won't play ball. I'll photograph it outside in natural sunlight tomorrow.
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Old 2nd Feb 2016, 7:17 pm   #8
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Default Re: What are these devices?

If you ever find a TO3 can where diode junction tests imply it's a PNP transistor with base to the can, it isn't. It's a double diode to use as a biphase rectifier, they turn up in some old PSUs.

I don't think a regulator will test as a transistor on diode test.

Assume it is a transistor. You can find base pin and whether it is npn or pnp. Does it match the pinout given above (there are few, if any, TO3 power transistors where the case is not the collector). Try testing it as a transistor.

I had guessed the 7828 was the date code (week 28 of 1978) and T484 is a house number.
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Old 2nd Feb 2016, 7:21 pm   #9
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Default Re: What are these devices?

The can isn't the base, as you say in a transistor it's generally the collector. One of the pins was the base and the other the emitter. I don't remember whether it was PNP or NPN though.
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Old 2nd Feb 2016, 11:03 pm   #10
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Default Re: What are these devices?

I'd guess 7828 is the date code. I'd say Texas Instruments but that's extremely speculative, so I'll wait for the picture before I say more dumb things.
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Old 2nd Feb 2016, 11:10 pm   #11
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Default Re: What are these devices?

Don't forget that most analogue IC processes use reversed diode junctions against the substrate as insulation for internal devices and connections, so finding diodes between various pins is inevitable, but they won't be shown on equivalent circuit diagrams.

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Old 3rd Feb 2016, 1:14 pm   #12
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Default Re: What are these devices?

that may be a Thorn part number for a tv or audio unit but I don't know the original part number
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Old 3rd Feb 2016, 5:28 pm   #13
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Default Re: What are these devices?

Here's a picture.

With the device inverted and aligned as in post #5, it tests out as a PNP device with the base connection being the left hand lead. There is no leakage from C to E either way.
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Old 3rd Feb 2016, 5:35 pm   #14
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Default Re: What are these devices?

The logo is that of Texas Instruments (TI).

http://inventors.about.com/od/Corpor...truments_3.htm

Their UK production-plant was in Bedford: http://www.electronicspecifier.com/a...ars--in-europe
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Old 3rd Feb 2016, 5:43 pm   #15
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Default Re: What are these devices?

That makes sense, because in 1978 I was working in Bedford and knew people who worked at TI.

I can't remember what I might have obtained the devices for though!
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Old 4th Feb 2016, 5:54 pm   #16
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Default Re: What are these devices?

I seem to remember that TI (Bedford) were making power silicon-diffused mesa transistors for use in TV line output stages (e.g. BUY69A) and if I remember correctly they were making experimental parts, hence the unusual number, with a higher breakdown voltage for use in a sequential-colour (10kV for orange/16kV for red) radar display. If the base and emitter terminals have more than the usual glass insulation around them it could be one of these. The other giveaway is a very low current gain ~less than 5 at 1A. The numbers either side of the logo form the date code as mentioned.
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Old 4th Feb 2016, 8:00 pm   #17
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Default Re: What are these devices?

Texas had a Semiconductor manufacturing plant in Plymouth as well.

No idea what they made there I went for an interview in 1975 I think it closed in 87?

Perhaps someone remembers

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Old 4th Feb 2016, 8:29 pm   #18
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Default Re: What are these devices?

Quote:
Originally Posted by BottleMan View Post
I seem to remember that TI (Bedford) were making power silicon-diffused mesa transistors for use in TV line output stages (e.g. BUY69A) and if I remember correctly they were making experimental parts, hence the unusual number, with a higher breakdown voltage for use in a sequential-colour (10kV for orange/16kV for red) radar display. If the base and emitter terminals have more than the usual glass insulation around them it could be one of these. The other giveaway is a very low current gain ~less than 5 at 1A. The numbers either side of the logo form the date code as mentioned.
I'm wondering if this is the same as was mentioned in "The Setmakers", where the Thorn TV-designers, having decided to do an all-semiconductor colour TV, found that the high-voltage TI transistors (which had originally been specified for a military radar) failed distressingly-often in the LOPT and EHT-generator stages and they were "steadily filling glass sweet-jars with burnt-out transistors at 14 a time" ??


[See page 379 of "The Setmakers" for more...]
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Old 4th Feb 2016, 9:46 pm   #19
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Default Re: What are these devices?

Quote:
Originally Posted by BottleMan View Post
If the base and emitter terminals have more than the usual glass insulation around them it could be one of these.
The only thing I've got to compare it with is a 2N3055 and they both have the same amount of glass.
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Old 18th Apr 2017, 3:31 pm   #20
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Default Re: What are these devices?

Put one of these on my Peak Atlas DCA55.

NPN Silicon Transistor.
Case is the collector.
hFE = 27
Test Current Ic = 2.50mA
VBE = 0.6V
IB = 4.81mA
Leakage = 0
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