BC108C equivalence

[Magister]

Hi, first post here, I am more a software guy than an hardware guy but I like to play with electronics nonetheless

I am looking for a BC108C equivalence, for an antenna preamp for my car radio, the schematic comes from an old book and is like this:

**broken link removed**

I searched for cross-reference and found a lot of "roughly equivalent", I also found the NTE123A, but I would like to be sure as the "C" in 108C seems to mean a special characteristic.

TIA!

 

[Nigel Goodwin]

The C is just a gain rating, pretty well any small silicon NPN should do (as long as it works to a high frequency - and most do). BC is actually an audio transistor, BF would be RF.

 

[audioguru]

I think the antenna preamp circuit will be overloaded by all the very powerful AM, FM and TV stations in a big city. They would cause severe cross-modulation.

The circuit was used when there one only one or two low power stations in the entire country.

 

[Nigel Goodwin]

You're rather assuming everyone lives in a big city - in which case he wouldn't be needing a preamp!

 

[Magister]

In Montréal there is powerful stations, but I often listen to some that are weaker, in my previous car which had a fender telescopic antenna I had no problem, but in my new car the antenna is embedded into the rear window (with the defrost?) and the station I used to listen has more noise and sometimes my radio even lose it, this is why I wanted a preamp, for the weaker stations.
Will it still work?

 

[Nigel Goodwin]

In Montréal there is powerful stations, but I often listen to some that are weaker, in my previous car which had a fender telescopic antenna I had no problem, but in my new car the antenna is embedded into the rear window (with the defrost?) and the station I used to listen has more noise and sometimes my radio even lose it, this is why I wanted a preamp, for the weaker stations.
Will it still work?

I wouldn't say it's a good choice - but it's cheap to build, so give it a go - do you have a layout for it?, as it's likely to be fairly critical.

 

[audioguru]

The preamp's input is not tuned. So the powerful stations will overload it and the weak stations will not be heard.

 

[Nigel Goodwin]

The preamp's input is not tuned. So the powerful stations will overload it and the weak stations will not be heard.

But it's cheap and easy to try! - even a tuned one is only going to be broadly tuned - you can't track the tuning in an external preamp.

 

[Magister]

I doubt now as we have a station every 0.2MHz...

Also I will build it on a small PCB, point-to-point soldered wires.

And for the BC108C, the NTE123A will work?

 

[audioguru]

I think the preamp is designed for 1MHz AM radio stations. It won't have much gain at 100MHz for FM stations.
A good FM receiver has tuning before the RF amplifier transistor or FET so that other stations don't overload it.

The NTE123A is completely different than a BC108C. Its minimum current gain is 8.4 times less and its datasheet does not say what is its typical current gain.

The circuit is simple so try it. I think it will be overloaded by all the AM radio stations in Montreal.

 

[Hero999]

How old is the BC109?

Does anyone still use it?

Use a more modern transistor like the PN2222A.

 

[Nigel Goodwin]

How old is the BC109?

Well it's the BC108 we're talking about

Does anyone still use it?

Yes, both 108 and 109.

Use a more modern transistor like the PN2222A.

What do you have against European transistors and 'proper' numbering?

 

[audioguru]

The BC108 and BC109 had old metal cases. They are listed in my Philips 1968 transistors manual. They were replaced long ago by BC548 and BC549 in newer epoxy (plastic) cases.

 

[Hero999]

What do you have against European transistors and 'proper' numbering?

Wht do you mean?

I thought nearly all transistors were made in China these days.

 

[Nigel Goodwin]

Wht do you mean?

'BCxxx' is European pro-electron coding, which tells you it's a silicon (B) general purpose audio (C) transistor.

There are still plenty of European transistors made and available, why suggest foreign numbers?.