I know this is an old PNP germanium transistor magnetometer design, but is it likely to work? I'd like to build and demonstrate this magnetic field detector for a class as an example of 1960s technology when comparing it to modern equivalents. (Magnetism is our topic this month.)

As far as I can see it's just a audio amp with a Darlington pair (TR2/3) but not sure what happens after that!

By the way, TR4 is shown E-C swapped over in error.

Thank you.

Janet W

 

If you are building this from scratch why do you want to duplicate that same circuit exactly?

 

I know this is an old PNP germanium transistor magnetometer design, but is it likely to work? I'd like to build and demonstrate this magnetic field detector for a class as an example of 1960s technology when comparing it to modern equivalents. (Magnetism is our topic this month.)

As far as I can see it's just a audio amp with a Darlington pair (TR2/3) but not sure what happens after that!

By the way, TR4 is shown E-C swapped over in error.

Thank you.
Janet W

It looks more or less OK - ish.

You might need to go round the voltages and fault find a bit to get it working.

Not entirely sure - but new old stock germanium transistors may deteriorate that long in storage. Silicon transistors would be scrap if as leaky as you're likely to find germanium parts.

You could probably get away with silicon transistors if you had to. The simple bias is a mixed blessing - not many parts to change, but you end up fiddling about manually setting the collector operating point with a high resistance pot in place of the base resistor.

 

If you are building this from scratch why do you want to duplicate that same circuit exactly?

Thanks Mr Chips and Ian F.

Yes, I'd like to build it as close to the original as possible (I have a number of modern equivalent circuits for comparison), although some of of the electrolytic capacitors seem a bit low in value. We have all the old transistors tested and working - they're not the AF### types that grow the tin whiskers inside.

Maybe an old Post Office relay coil will do as the pick-up, although some experimentation may be required here.

This is to demonstrate to the iPhone generation that all manner of electronic designs were possible before 1999! This particular circuit was presented for reproduction - hence my interest.

Janet W