Rosemary Ainslie Circuit Demonstration, June 1 2013

[TinselKoala]

"So What?"

Do you see? She is now preparing to admit that the Q1 is indeed failed in the Figure 3 scopeshot... but she is claiming THAT IT DOES NOT MATTER.

[picowatt]

I'm curious why I would need to protect it to a level well below its output capability?

.99,

Is the PG spec'ed to drive the ouput shorted to ground indefinitely at that 10volt level or is it only spec'ed into a 50R load?

I would want a fault to blow the fuse as quickly as possible to limit voltage rise as well as current.

As I added in my previous post, I would be as much or moreso concerned about overvoltage spikes than overcurrent. Even the fuse arc voltage would concern me.

Hi speed output designs (fast rise times) of that era (Tek gear at least) were often a bit fragile concerning overvoltages.  I have not seen your HP's schematic/manual, but I know it is often a pain when any of my Tek gear goes down regarding finding parts or crossing to newer ones (and Tek liked using custom hybrids).  So if I was using one of my older Tek PG's or FG's to test this circuit, I'd want to do as much to protect it as possible.  I would also check the output section to see what the wattage on the internal 50R is and take a quick look at the output devices thermal management setup (heatsinks).

If you have the schematic for your HP, you could look at the output circuit and see if there are two diodes from the output to the supply rails to clamp overvoltages.  This is common on lower speed designs, but often omitted on fast rise time circuits due to their capacitance slowing things down a few ns.  If the diodes are there, you'll likely be OK with just a fuse.  If not, I'd add the zeners I suggested.  I'd mount the zeners and the fuse in the smallest diecast Bud box (abut 1.5X1.5X1") with a BNC mounted at each end and use a double ended BNC adapter to plug the box directly into the PG output (to minimize inductance between the zener clamps/fuse and the PG output).   

Either way, you'll be better off with just a 250ma fuse than no fuse!  Just take your time, insulate your PG connections and the supply rail connections reasonably to minimize accidental contacts, and keep an eye on device temps.

Looking forward to seeing your test results!

PW

[picowatt]

"So What?"

Do you see? She is now preparing to admit that the Q1 is indeed failed in the Figure 3 scopeshot... but she is claiming THAT IT DOES NOT MATTER.

What really matters is how long it has taken her to even come close to admitting that there was a problem with Q1 in FIG3.  Her team of "engineers" should have been able to recognize this immediately, particularly when it was first brought to her attention a very long time ago.  She should have immediately redone her tests and retracted/corrected her papers with the new data.

As well, the time wasted attempting to teach her how to read her scopes and her schematic,  her constant argumentative attitude and misquotes, and her subsequent character assassanations matter.   

If all her new demo is going to show is how easy it is to produce the neg mean pwr figure, or produce oscillations, I have little interest in watching it.  The fact that the oscillations and neg pwr measurement can be produced has never been in dispute and both .99's simulations and TK's replications have readily confirmed this. 

If she was going to show how easy it is to apply +12volts to the gate of Q1 and not have Q1 flow any current, that would be quite interesting, as the challenge would then be to discover the required trickery used to do so.

I am, however, quite interested to watch .99's work as his time permits.

PW

[poynt99]

PW,

This model at least has a current output (common base) amplifier, not voltage. So the 50 Ohms looking back into the output port is a resistor to ground, not in series.

Since it is a current output, surely the generator can tolerate a dead short on its output, otherwise it wouldn't be worth a damn to the professionals using it. Any FG for that matter that can not tolerate a dead short indefinitely at full output should be tossed in the garbage imo.

It does have output voltage protection as well. They call it "Excessive Voltage Protection" using a few diodes and a transistor for each half.

I have some 15V TVS diodes at work; I will install them as well as the 250mA fuse as a precaution.

[picowatt]

PW,

This model at least has a current output (common base) amplifier, not voltage. So the 50 Ohms looking back into the output port is a resistor to ground, not in series.

Since it is a current output, surely the generator can tolerate a dead short on its output, otherwise it wouldn't be worth a damn to the professionals using it. Any FG for that matter that can not tolerate a dead short indefinitely at full output should be tossed in the garbage imo.

It does have output voltage protection as well. They call it "Excessive Voltage Protection" using a few diodes and a transistor for each half.

I have some 15V TVS diodes at work; I will install them as well as the 250mA fuse as a precaution.

.99,

As it states that it has "EVP", you'd likely be fine with just a fuse, but the TVS diodes might add a bit more protection.

Looking forward to seeing your experiments...

PW