Need help determining components for a circuit.

[tommis15]

I have an old Science Fair kit for a radio. I am a beginner at electronics and I don't know if it's AM or FM. The kit was given to me because components were missing and it was going to be thrown out.

I will attach a picture of the kit... can someone help me find the components I need and tell me if it's AM or FM.



I know the diagram shows 2SB and 2SA for the transistors but when I googled there were many 2SB and 2SA transistors. I was also told that these were Toshiba transistors. The guy throwing it out said something about 2sa52x and 2sb56x. I googled and found an equivalend for the 2sb56x called nte126 but couldn't find that on ebay canada. I couldn't find an equivalent for the other one though. I don't know if they still make them or not... If they don't I would appreciate if someone could help find an equivalent.

Then there was a diode but I don't know which one... I was told it was glass...

Also there is short and long antenna... How long should each one be?

It says earphone so I guess that normal speakers won't work? I'm not sure... How much resistance between speaker/earphone?

Thanks for any help!

 

[KrisBlueNZ]

That's an old AM radio. It's actually just a crystal set with a two-stage audio amplifier.

The two transistors are old Germanium PNPs. Yes, Toshiba did make these, but so did other companies.

You're right, there are many "2SA" and "2SB" transistors.

2SB transistors are designed for use at low frequencies, i.e. audio frequencies.

2SA transistors are designed for high frequencies and would be used for the first stage if it was an RF (radio frequency) amplifier, but it's not. So you can also use a 2SB transistor for the first one.

In practice, almost any small germanium PNP transistor with a 2SA or 2SB prefix will work in both positions. 2SB56 is (was) a common germanium PNP transistor and would be suitable for both positions. The NTE126 looks suitable - in fact it's a high-frequency transistor, but any small-signal germanium PNP such as an AC128 will do as well.

The diode should be a germanium diode such as an OA91.

Right, speakers will definitely not work. It's probably designed for a high-impedance headphone - 1 kilohm or so. These aren't widely available. But you can feed the signal into your stereo, if you connect a DC blocking capacitor (e.g. 1 µF) in the signal path (positive side to amplifier input).

 

[tommis15]

For the transistor can you tell me which would be the best on the following page:

https://www.taydaelectronics.com/catalogsearch/result/?q=2SA

For the diode would any of these work:

http://www.taydaelectronics.com/diodes/germanium.html

you can feed the signal into your stereo, if you connect a DC blocking capacitor (e.g. 1 µF) in the signal path (positive side to amplifier input).

I'm a noob in this stuff, so just to make sure... what pins in the image does the cap connect to?

Also what about the antenna length?

 

[duke37]

Transistor
2SA1015 50V 150MA, this is a bit unlikely, it is probably 150mA
Gain about 100.
According to my book it is a silicon dvice and would need different biassing. Perhaps my book is wrong. 2SA numbers under 480 are shown as germanium
Quite an acceptable price.

Diode
1N34 I have not looked up the specification but it seems to be a familiar number.
There seems to be some confusion about the 1N60 diode. This was a popular germanium diode and is now sold as a silicon schottky diode, I have bought some and they seem to have a similar voltage drop to a germanium device.

The set should have a ground connection at the bottom left and the antenna should be connected to one of the connections at the top left. Choose the one to give the best compromise between strength and selectivity.

 

[KrisBlueNZ]

As duke37 says, the 2SA1015 is silicon, not germanium. None of the 2SA devices on that page is germanium. You can use any small-signal 2SA or 2SB transistor that's germanium. Other suitable germanium transistors are AC126 and AC128.

The 1N34A should be fine.

 

[tommis15]

Ok. So I have a better idea of what I need to make this so that's great. Thanks.

Just to confirm:

AC126 * 2
1N34A * 1

I'm having trouble locating that transistor too... I can buy it on ebay but the prices are outrageous and the shipping is even worse since it all comes from russia, bulgaria, czechoslovakia, etc...

If I use that 1 uf cap could I get it to work with normal speakers (computer speakers)?

Are 1/4W resistors good enough or should I go for a higher wattage?

 

[KrisBlueNZ]

Yes, you need two PNPs and a diode.

Radio Shack have a few: http://www.radioshack.com/product/index.jsp?productId=12651122

If you put your location in your profile, I can search for suppliers near you.

Adding the 1 µF capacitor will not enable you to drive anything less sensitive than high-impedance headphones or an amplifier.

1/4W resistors are fine.

 

[tommis15]

I bought AC128 off of ebay. I actually checked and I had some 1N34A's. I just bought a ceramic high impedance earphone on ebay. I hope that's good enough. I just need to go shop for some resistors and caps. Thanks for all the help. I need to wait for the components to come in the mail so I might not respond for a while.

 

[tommis15]

I got the transistors today! The seller shipped me 4 ac128 and 4 unknown transistors and a ton of diodes. I ordered 4 transistors and got a ton of stuff. It might take another 2 weeks to get the other components. I got cheap shipping, I'd rather wait instead of paying 3-4 times the cost of the component on shipping.

 

[KrisBlueNZ]

Cool

 

[tommis15]

Anyways, here is a shot of the diodes I got. Very low quality, but the best I could get since it is very small. My camera is very bad and it doesn't focus well.

They are glass, they have 2 yellows stripes on them.

 

[tommis15]

Please help identify.

 

[KrisBlueNZ]

The image you linked to can't be viewed. imgur says it "cannot be displayed because it has errors".

 

[duke37]

The common small silicon diodes are 1N914 and similar 1N4148.

Yellow is 4, look up the other colours.

 

[KrisBlueNZ]

I think I've seen two yellow stripes on some germanium diodes. I don't know what they signify (apart from marking the cathode end). 1N44, perhaps?

If the stripes are yellow, brown, yellow, grey, then yes, it's a 1N4148.

Can't say one way or another without a picture.

 

[tommis15]

I removed the image now, since you said it wasn't working for you. Anyways, as I checked my email for the imgur deletion links that I had sent to myself, I realized the seller contacted me. He told me they were SFD106-112 diodes. Are these better for the circuit, or should I stick to 1N34A. I did a google and http://english.electronica-pt.com/components-cross-reference?ref=SFD106 led me to believe that these diodes are similar to 1N60.

Thanks for all your help and have a great weekend!

 

[KrisBlueNZ]

I Googled that part number, SFD106. It's clear that it's a germanium diode. Two sites say it's a UHF/Microwave detector diode; one says it's a "Germanium point contact diode intended as AM demodulator." I haven't been able to find a data sheet, or even the name of any manufacturer. Most likely it will be fine for this application.