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Here is a really interesting microscope photograph and analysis of the insides of a TL084 op-amp: http://www.righto.com/2018/06/silicon-die-analysis-op-amp-with.html, link posted by marcelomd over at DIYSB.  The author breaks down the structure of the various transistors and why they are shaped that way.  The amount of engineering that goes into even a "simple" op-amp has always impressed me.

Of note re the recent discussion of the LM308 and its need for an external frequency compensation capacitor, you can see that the TL084's internal capacitors are the largest area on the chip, even though they are a very small value cap (because there's no high-dielectric material to work with).

It's a Ruby amp (LM386) on veroboard built into the enclosure of a desktop PC power supply. The speaker was salvaged from an old intercom unit, and actually doesn't sound too bad. Though a slightly larger real guitar speaker would fit, and probably sound a little better.

Hi gang,

There have sometimes been questions about cheap DIY oscilloscope kits here. I just built one and will post some pictures and comments. Feel free to use this thread to ask questions, post your own kit experiences, or suggest things for me to try it on to test its usefulness.

The kit I got is a DSO 150 made by JYE Tech: http://www.jyetech.com/Products/LcdScope/e150.php  This is supposed to be an improvement on the DSO 138 model that I've seen a few posts about. Notable changes include a rotary encoder for setting parameters (like volts/div, sec/div) and that it comes with a compact housing.  I got mine from the inartfully named banggood.com, which sells a lot of electronic kits and whatnot. (And drones. Prepare to get marketing emails advertising drones.) JYE Tech says there are a number of knockoff sellers on ebay or aliexpress, so be aware of that.

I got a version that has all the SMD parts pre-soldered. It was just US $20.
I should have ordered an inexpensive function generator kit at the same time.

This is what comes in the box, including 2 sheets of nicely detailed and legible instructions. A main board with display, analog board, bag of components, clip leads with BNC connector, and plastic case.

Edit: you will also need a 9 vdc center positive power supply.

The general Baby Board 1590A build guide isn't linked from either the Shop page or the tutorials. (It turns out I have a saved copy anyway.) Or did it become obsolete in some way? I see that many of the current baby boards have some way of board mounting pots.