One was how to implement a 30 uA current source in a scope (early 1970's, solid state chassis with a CRT).

Did they define the stiffness required for the current source?

 

When I was in school, Tektronix was on campus recruiting, and came with a short quiz with some real-world problems. One was how to implement a 30 uA current source in a scope (early 1970's, solid state chassis with a CRT). The answer they were looking for was a single 10 M resistor to the regulated +300 V plate supply.

ak

I once had a _really_ old Tek scope. It started with 800 volts regulated it to 400 volts and then used a resistor to charge a cap to get the "linear" horizontal sweep sawtooth. The sweep was 20 volts p-p.

http://w140.com/tekwiki/wiki/513
bee.mif.pg.gda.pl/ciasteczkowypotwor/Tek/513.pdf

 

Hi,

i already found a few circuits but i really need it to to be small.

Similar to this

Any suggestions?

Thanks!

For super easy, just use an LM317 and a resistor.
Good for about 4V to 35V

Maximum heat at 35V voltage drop is about 0.5watt (turn down your power supply voltage when working in solutions that are high conductivity) or use a small heat sink. If you can keep your supply voltage within 15V of your electrolysis voltage, you won't need a heat sink.

The LM317 is one of the most common chips and can be found anywhere for $1 to $3 each.

Note (GND pin will be labeled ADJ on a real LM317)

 

I once had a _really_ old Tek scope. It started with 800 volts regulated it to 400 volts and then used a resistor to charge a cap to get the "linear" horizontal sweep sawtooth. The sweep was 20 volts p-p.

I've crawled around in a lot of gear in many different industries, and *nothing* compares to Tek power supplies. Those boys were just plain strange. And it wasn't just their scopes - their broadcast pulse and test gear were just as weird. Diagnosing a Tek scope supply was a graduate course in circuit analysis.

ak

 

See

 

I've crawled around in a lot of gear in many different industries, and *nothing* compares to Tek power supplies. Those boys were just plain strange. And it wasn't just their scopes - their broadcast pulse and test gear were just as weird. Diagnosing a Tek scope supply was a graduate course in circuit analysis.

ak

I can attest to that, having recently fixed the power supply in my Tek 2225 scope.

 

I've crawled around in a lot of gear in many different industries, and *nothing* compares to Tek power supplies. Those boys were just plain strange. And it wasn't just their scopes - their broadcast pulse and test gear were just as weird. Diagnosing a Tek scope supply was a graduate course in circuit analysis.
ak

The oddest circuit I can think of is in the FG504 -- a 40MHz function generator. It uses a dual differential pair inside a CA3102 to make a voltage comparator . That part makes sense.

What I have never figured out is why they drive the _substrate_ pin on the CA3102 transistor array.