Recent content by VA7JHI

I'm through with AliExpress. They talk big talk about returns and refunds. But their process is inscrutable when you actually try to use it. Their listings are deceptive — perhaps through incompetence rather than design. I ordered a camera lens cover. It comes in varieties. The one in the...

I have a kilowatt power supply, Raytheon-Sorensen 40-25B. up to 40 volts at up to 25 amps, coarse and fine adjustable volts and current. But it trips the ground-fault breaker my "tech trailer" is plugged into when I plug it in. I stuck a DVM set to the highest resistance range across either...

One of my two drill batteries stopped working. I opened it up, and measured all five cells. One was very low compared to the others. I pried the spot welds off and worked the battery out of the pack. (It was in the centre.) I worked a new cell into the pack, and spot-welded it to the old...

I understand the rules and wish to enter into the drawing.

I don't have the time to explain this to the nay-sayers. ( Links removed by Admin)

It doesn't. It's the ratio of R10 to R11, both of which have the same value. That sets the AC gain. The cap allows it to have a different DC gain. It self-biases at 0.6 volts DC.

But with the given feedback resistors, it's running at unity gain. By your logic, just about any op-amp design should be an oscillator.

That's only possible for a gain of two or less. Unless you want an attenuator! fT is defined as the point of unity gain in a gaussian (6db/octave) roll-off. Oh yea. Like I really need one more project… :-)

As an RF Engineer, I've done dozens of such designs. This one might work a bit better with high ft transistors with some PCB layout tweaks, but I see nothing obviously wrong with it.

That's what bypass caps are for. I see several of them in the circuit. They need to be physically close to the high ft transistor. I'd rather have too much ft than too little!

R10/R11 and R13/R12 provide negative feedback. It appears to be set for unity voltage gain (1k for both resistors). I imagine the input transformer supplies needed voltage gain, and the push-pull output only supplies current gain. Regarding having the "wrong frequency" for the transistors...

I understand the rules, and wish to enter the contest. I promise to post an unboxing and plaster it all over social media if I win. ("PICK ME, PULEEEZE!")

Well, the first one I bought would put out 20 amps at 40 volts into a 2Ω load (800 watts) on a giant heat sink, pretty much indefinitely. Then, I ordered four more. Whenever I hear someone say "such devices" I know it means they don't have any experience with the specific device I was talking...

Try this. <—LINK That will give you 24VDC at 12A from 12VDC… at least, according to the specs.