Trio Amplifier KA-2002A mystery component

[Richard_FM]

Until 2 years ago I was using my Dad's old amplifier with my laptop's sound output.

The sound quality was usually good but adjusting most of the controls seemed to produce lot of noise through the speakers.

Recently I've been cleaning it up internally, especially as there seemed to be years of dust trapped inside, which I carefully brushed out with a half inch paint brush.

After doing that I have all the pots & switches a dose of switch cleaner.

All of this work seemed to do the job & it's now working alright with no sound from the controls.

While doing this I could smell a lot of that old electronics smell that seems to be common on vintage technology made up to the mid 1970s.

While cleaning the dust out I found a loose component in the interior, it's brass cased with a tag, a clear domed top & 2 legs that look unsoldered.

The number seems to be: 1842 M 811, I'm not sure where to start reading from.

I'm guessing it's a diode of some sort.

Considering it's been in there 40 years I'm surprised it's managed not to short out anything, & no-one had heard it rattle around at any time.

I've tried to photograph the component but it's small size makes it tricky, even with my camera in macro mode.

I think there has been a thread before about things found in devices.

[paulsherwin]

It looks like a light dependent resistor (LDR), but I've no idea what one of those would be doing inside an amplifier. It could also be an early LED.

[Refugee]

It looks like a "posh" photo diode.
Have you measured it on a diode tester?
If so does it respond to light while it is on the diode tester?

[Herald1360]

Looks like a LED. Or maybe a photodiode.


See if you can find its forward voltage drop with a DMM diode check.



In the dark you may see some light outoput if it's a LED.

[Refugee]

Originally Posted by Herald1360

In the dark you may see some light outoput if it's a LED.

That might not be so if it is an IR LED.

[Radio Wrangler]

I suspect it is not a native resident of the little Trio. Unless it's the 'ON' indicator light?

It might have fallen in through a vent or been one of those things fired across a workshop by sidecutters.

David

[Boater Sam]

Eye of Horus, beware of weird looking dogs following you.
Don't peer into it too long,
Looks like an IR diode to me too.

[julie_m]

A couple of quick tests with a multimeter, each way around in the dark and in broad daylight, should show whether it's a source or a sensor. If it passes a current one way only in light and not at all in darkness, it must be a photodiode or phototransistor. If it passes a current both ways in light but not in darkness, it must be an LDR. If it has a forward voltage drop greater than about 1.5V, it must be an LED; if it is emitting a visible wavelength, you might even be able to see a glow, but not all meters can put out enough voltage to light an LED.

[rontech]

I seem to have read somewhere that an LED can be used to establish a stable (low) voltage in a circuit. Maybe a bit like a zener diode?

[julie_m]

A little bit, but LEDs used as voltage references are usually forward-biased. (They do actually exhibit constant-voltage behaviour in reverse breakdown, but the PIV is not accurately specified. Good noise sources, though!)

[Herald1360]

Originally Posted by Refugee

That might not be so if it is an IR LED.

Look at it with a phone/digital camera- IR shows up on those as a purple colour, at any rate for the LEDs in remote control handsets.

[Richard_FM]

Thanks for the suggestions I'll have to see what I can test with my multimeter.

[snowman_al]

My guess is it is a TO-18 cased LED...
Lead closest to the tab will be the Anode. Could be any colour but IR most likely. Nothing to do with the old Trio though.
Alan

[Richard_FM]

In the 1970s infra red wasn't even common in remote controls, as most early ones had ultrasonic communication.

[Refugee]

It looks too "posh" to have come out of a remote control.
I have got a 4-wire one that is an IR LED and a matching Photo device in a TO18 can.
The photo shows it being prepared for use.

[snowman_al]

Originally Posted by Richard_FM

In the 1970s infra red wasn't even common in remote controls, as most early ones had ultrasonic communication.

You are correct, but I doubt very much if it is contemporary with the Trio being built...

[Richard_FM]

That makes things even more interesting, I don't remember my Dad ever taking it to anywhere to be repaired at any time.

[Radio Wrangler]

I wonder if it was a bit of Trio's production machinery that fell off and dropped in?

Those sorts of parts did exist at the time, but as said earlier in the thread, it's a bit posh and expensive to be part of the product.

David

[Richard_FM]

That's a possibility.

The quality of the amp in general is good, with a sheet steel case including a thick alloy plate making up the base.

[Boater Sam]

Sensor from a CD player or a disk drive? Its not a cheap plastic one so could be a good find.