Oscilloscope info

The 185 sampling scope was stunning. Heavy and ugly, but stunning. Dual-trace, 5 GHz bandwidth, about 10 ps RMS jitter, using *tubes* in about 1962.

John

I hear their new $995 color LCD scope is pretty nice. But then, it's actually a relabeled Chinese scope.

John

The quality of the output device substrate PNP determines a great deal of the distortion. Motorola's were useless in active filters.

...Jim Thompson

Good Lord. It is indeed 3 junctions.

No quiescent output stage bias whatever,

And ppl suggest these for audio amongst other things ! ?

Graham

Wasn't tht the one with an impossible to reach fuse in it?

The one where they build the oscilloscope by laying the fuse on the production line and assembling everything else around it?

Insane, huh? How much would a couple of diodes cost?

Golden ears indeed.

Adding a pulldown on the output pin helps a lot... becomes a class A opamp output stage!

John

Ah yes, used that trick even with 741s and 748s to keep them class A. Ummm - around 30 yrs ago in fact !

Graham

Is it that bad ?

Rene

That also depended on brand. Some knew how to do the mirror bias to prevent crosstalk.

Not *any* input... just a *certain* input ;-)

...Jim Thompson

I use two 54542a since 24 months now and I am quite happy with these. Regarding accuracy, user interface and signal quality they are OK. I higly appreciate that all functions are already included (you do not have to pay extra for FFT or so) and saving/recalling setups is quite fast - or at least faster than on contemporary TEK scopes.

So I do not really understand the issues of the other people who do not like the HPs. The only thing I fear in the 54542a's is that the included FLASH memory or CPLD may get corrupted which will render the instrument useless.

Best regards,

Erik.

Not National. If one section rails, you get huge (as in volts-level) spikes out the other three.

The classic National datasheet has a footnote in 1/2-point type that hints that weird things happen if any input is pulled below ground. Something like -0.3 hoses charge all over the chip. Is it only on certain inputs? This sure burned me a couple of times.

LM339 does the charge-spray thing too. I wonder if anyone has actually used this "feature" to advantage.

John

No "spray charge" to it. Depending on input, at about a Vbe below ground the mirror load on the lateral PNP diff pair saturates. The positive input, when taken that low, causes the output direction to reverse.

There is no current limit, so caution with low-Z input sources.

There was a time when I considered the LM324 and the LM339 to be "God's gift"... used them everywhere. I still like the LM339 if you don't need high speed.

...Jim Thompson

And at higher currents, it will reverse yet again.

But it can trash the other three amps, too!

John

I've got a Tektronics 545 that makes a great space heater. ;-)

"John Larkin" a écrit dans le message de news: snipped-for-privacy@4ax.com...

Yes to press where it hurts :-) Once "someone" designed a cpu board without bothering about BUS matching. Later he told me he didn't _believe_ those stories about TLines. The net result was an intermittent "software bug" in the CPU UART. A bit of investigation showed that the UART XTAL oscillator sometime stopped and slowly resumed a few ms later. More investigation showed that the databus surrounded the XTAL connections, and that the oscillator stopped when a high 1 bit count byte was read from the farmost RAM on the bus. Of course that ram was quite fast and quite far. Brilliantly "fixed" by the moron by pluging schottky clamps on the most conveinient place (on a daugther board, right in the middle of the BUS) where some diodes totalized about 100nH serial parasitics. Then run $50K worth daughter board with the success you imagine. Unfortunately the brilliant guy was the irremovable head of the engineering and design department and lot was to his image. So I did press as hard as I could... and left.

I have a 561A that just takes up space. I replaced it with a 32Ms/s pc-based parallel port scope.

No, that's what my old Polarad spectrum analyzer is for, and the fan noise is to keep you from falling asleep. ;-)

Duh, my wife could dry her hair with the airflow coming from my DAS9200 logic analyzer :-) In the winter I install more boards for better heating. Its 1900VA power supply doesn't care.

I don't know about that. After a few hours of that dull roaring noise, I start to think I hear voices embedded in it. Something telling me about 'a hockey mask and an axe', or something like that.