Dual Trace /Electronic Switch build

[Smithdoor]

Here one I just found from Electronic World 1964
https://www.worldradiohistory.com/Ar...ld-1964-02.pdf

[Smithdoor]

Here is a online oscilloscope

https://academo.org/demos/virtual-oscilloscope/

[Jez1234]

Originally Posted by Craig Sawyers

I'd copy a circuit from eg the Tektronix 453. All discrete, with ch1/ch2/chop/alt/add switching too. 50MHz bandwidth.

But your options are going to be of very limited bandwidth with simple potentiometers as input attenuators. Switched attenuators with careful compensation are essential if you want a bandwidth more that a few hundred kHz.

Craig

That's where the fault was in my 453. Just a transistor in the end but I'm guessing the fault was what put it in abeyance probably not long after the guarantee ran out hence it being near as damn it NOS when I got it

[mhennessy]

Interesting... I appreciate that a high bandwidth is not required, but I'll be interested to learn what the bandwidth is like once it has been finalised. Using a 500k potentiometer straight into a common-emitter amplifier which might present significant input capacitance that might be increased by Miller effect - not a promising idea. As Craig suggested earlier. BTW, the fact the transistors might have an fT of 250MHz does not mean you'll get anywhere near that bandwidth in a complete circuit - sorry if that's stating the obvious, but just in case...

Not sure how the input transistors are biased. Assuming you want to put analogue signals through this (it might be fine for TTL or similar). Note that circuits you refer to either have separate bias, or use JFETs with source resistance.

Also, the input protection is curious. One of the LEDs will prevent the base going too far negative, so that's OK, but the other one (right hand on your schematic) will never conduct because of the 0.6V Vbe of the transistor. So unless a resistor is added between the LEDs and the base of the transistor, it is redundant. But it would be OK if you were using JFETs.

For this, I'd consider a 4000-series analogue switch IC. Can be powered from plus/minus 7V or thereabouts, but single rail operation would be doable. Cheap, widely available, and decent performance. You could probably use a 4053, which is a triple dual-throw switch. One section can switch the signal, and the other two could be used to form the multivibrator, so no transistors needed - just a single 16 pin DIL package. Probably too late into the process for this suggestion, but worth bearing in mind for others?

[Smithdoor]

I am looking at 4066 switching chip and a LM358 op amp.
To make even simpler using a 555 chip for flip flop.

Dave

Originally Posted by mhennessy

Interesting... I appreciate that a high bandwidth is not required, but I'll be interested to learn what the bandwidth is like once it has been finalised. Using a 500k potentiometer straight into a common-emitter amplifier which might present significant input capacitance that might be increased by Miller effect - not a promising idea. As Craig suggested earlier. BTW, the fact the transistors might have an fT of 250MHz does not mean you'll get anywhere near that bandwidth in a complete circuit - sorry if that's stating the obvious, but just in case...

Not sure how the input transistors are biased. Assuming you want to put analogue signals through this (it might be fine for TTL or similar). Note that circuits you refer to either have separate bias, or use JFETs with source resistance.

Also, the input protection is curious. One of the LEDs will prevent the base going too far negative, so that's OK, but the other one (right hand on your schematic) will never conduct because of the 0.6V Vbe of the transistor. So unless a resistor is added between the LEDs and the base of the transistor, it is redundant. But it would be OK if you were using JFETs.

For this, I'd consider a 4000-series analogue switch IC. Can be powered from plus/minus 7V or thereabouts, but single rail operation would be doable. Cheap, widely available, and decent performance. You could probably use a 4053, which is a triple dual-throw switch. One section can switch the signal, and the other two could be used to form the multivibrator, so no transistors needed - just a single 16 pin DIL package. Probably too late into the process for this suggestion, but worth bearing in mind for others?

[Smithdoor]

This the schematic with label for building.

[mhennessy]

Have you tested your circuit yet, perhaps on a breadboard?

[Smithdoor]

Originally Posted by mhennessy

Have you tested your circuit yet, perhaps on a breadboard?

I do not have breadboard just pc boards and solder.
Try as good as can on drawing before soldering.

It should work

Dave

[Smithdoor]

Originally Posted by mhennessy

Have you tested your circuit yet, perhaps on a breadboard?

I ordered a breadboard today will here Tuesday

Dave