Testing the TK Tar Baby

[TinselKoala]

This circuit cracks me up, man.
You could go crazy following the current paths around in the various conditions of operation. The battery and the power supply wind up in anti-series, with one current loop from the ps going through the zener in Festus, around backwards and upstream through Moses back to the power supply,while Moses is carrying the main current going the other way,  and the other current loop going around the other way goes up through the load and back to the main battery. Or something. And in the other condition, negative bias oscillations, the bias is in aiding series with the main battery so that the load actually experiences more voltage than the battery supplies alone and some of the current sneaks past the CVR without being noticed and the load heats like a whale eats: by straining through a mouthful of whalebone. It's as complicated as the circulatory system of a hopping green amphibian.
No wonder RA is nuts. This circuit both is a product and a cause of her madness.

[TinselKoala]

@GL: did you notice the bias current starting at 90 mA and increasing on up to 130 or even higher over the space of ten or twenty seconds or so? I thought that this was so strange that I tried some new, unused PG50s as Q2 and they behaved the same way, with maybe a few mA difference...

[TinselKoala]

Uh..oh.
I just noticed something.

We have feedback oscillations, call them parasitic or resonant or whatever, they are the same thing as the squeal on a PA system when the mic is too close to the speakers.

And we have negative feedback, a different thing that is causing the main current to decrease when the Q2 is in, during the positive bias mode.

And we have negative bias, a different other thing that causes the oscillations to happen in the first place during the negative bias mode.

And we thought that the confusion between power and energy was bad.............



This circuit cracks me up, I'm telling you. I can hardly keep a straight face.

[TinselKoala]

@GL, you are welcome, I'm glad I could oblige. Can you explain the significance of our findings?

Also, I hope you will continue on and explore the negative voltage bias mode with oscillations and without Q1 turning on,  too. I already measured this mode using the oscilloscope last week and I found a small AC ripple on top of the usual 180 mA main DC current or so that I like to run at. In this mode it seems to me that the bias ammeter and the main ammeter will read the same, I think, and the current is DC but with that little ripple on top from the oscillations. This mode seems to put the bias supply voltage in series with the main battery voltage, I think.

[Groundloop]

@GL: did you notice the bias current starting at 90 mA and increasing on up to 130 or even higher over the space of ten or twenty seconds or so? I thought that this was so strange that I tried some new, unused PG50s as Q2 and they behaved the same way, with maybe a few mA difference...

TK,

Yes, I did notice that the current did go up as my heat sink did get warmer. But I'm
using a fairly large heat sink so it flattens out over time.

GL.