Anybody know what this is?

[StuUK]

Hi there

Anybody have a clue what this is? i took the can off so you can see the internals...

Picture attached and thanks in advance.

Stu

[Simon]

some sort of filter, not sure what the diodes are for.

[bktemp]

Could it be a Foster-Seeley discriminator (fm demodulator)?

[edpalmer42]

Is that a coil in the center (the long white cylinder).  Is there a tuning slug inside it?

Ed

[StuUK]

yes definitely a coil

[Tac Eht Xilef]

Could it be a Foster-Seeley discriminator (fm demodulator)?

Certainly looks like it.

[Paul Price]

It is either a Forster-Seely Discriminator or Ratio Detector demodulator for an FM radio.
Because the two germanium diodes are mounted in reverse to each other, it more likely a Ratio Detector.


https://www.google.dk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwid07uf_rHKAhUF6g4KHYTiA9cQFggqMAA&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FFoster%25E2%2580%2593Seeley_discriminator&usg=AFQjCNGjsyMxFG_glXz9VCQD-ZsaK1A5uw



Ratio detector
A ratio detector using solid-state diodes

The ratio detector is a variant of the Foster-Seeley discriminator, but one diode conducts in an opposite direction. The output in this case is taken between the sum of the diode voltages and the center tap. The output across the diodes is connected to a large value capacitor, which eliminates AM noise in the ratio detector output. The ratio detector has the advantage over the Foster-Seeley discriminator that it will not respond to AM signals, thus potentially saving a limiter stage; however the output is only 50% of the output of a discriminator for the same input signal. The ratio detector has wider bandwidth but more distortion than the Foster-Seeley discriminator.

But, if this device is from a premium Hi-Fi FM tuner, it is more likely to be a Foster-Seely discriminator because of lower recovered audio distortion, but if it is from a cheaper FM  or oldie boombox it would be the choice for cutting cost, so it would use a Ratio Detector.

[bills]

RF coils and I don't believe those glass devices are diodes, They are low value caps.
I have some in my junk box and they test as caps. (Let the debate begin)

[T3sl4co1l]

1N542 = Ge point contact diode, 45V 10mA.

I'm going to dissent from popular opinion, because the coils on top have far too many turns to be an FM detector stage (typically done at 10.7MHz).  And there are far too many coils and diodes for this to be just an FM IF/detector module.

The lower coils might be consistent with a ~45MHz TV IF stage, in which case the one diode (unmarked) should be detecting that, and the 4.5MHz audio carrier will be present in that detector output, which is tapped off by the top pair, and immediately detected.

So I think it's from a classic TV, probably 50s-60s era.

Tim

[AF6LJ]

1N542 = Ge point contact diode, 45V 10mA.

I'm going to dissent from popular opinion, because the coils on top have far too many turns to be an FM detector stage (typically done at 10.7MHz).  And there are far too many coils and diodes for this to be just an FM IF/detector module.

The lower coils might be consistent with a ~45MHz TV IF stage, in which case the one diode (unmarked) should be detecting that, and the 4.5MHz audio carrier will be present in that detector output, which is tapped off by the top pair, and immediately detected.

So I think it's from a classic TV, probably 50s-60s era.

Tim

I think you nailed it.

[StuUK]

Must admit my first thought was that it was likely from a really old TV.

I guess these days it's no use for anything and I've inherited about 30 of them

Thanks for all the help though.

[MrSlack]

Stick the diodes on ebay. Some idiot will pay £20 for them for a fuzz pedal or something 

[Simon]

Stick the diodes on ebay. Some idiot will pay £20 for them for a fuzz pedal or something 

You mean valued customer don't you ?  or is it valuable customer

[MrSlack]

Valuable

[StuUK]

Stick the diodes on ebay. Some idiot will pay £20 for them for a fuzz pedal or something 

You mean valued customer don't you ?  or is it valuable customer

Worth a punt I guess..... What are the diode types, can you tell from the picture?

[MrSlack]

The red/yellow/green ones are likely to be 1N542 germanium point contact detector diodes (1N,then read the colours like resistors; same code!). Seem to be popularish on ebay.

The other one with the orange band; no idea. If you've got a multimeter with a diode tester, check it with that after desoldering or clipping it out and post the forward voltage drop.

[StuUK]

Clipped one (the orange band) out and tested it with an Atlas DCA which read a Vf of 0.64v and an If of 4.77mA

[MrSlack]

Sounds like a boring old silicon one then. I'd ignore it. The Vf is too high for a nice germanium one.