Likely impedence of this scenario?

[Michael Terrell]

On Thursday, October 10, 2019 at 11:08:44 PM UTC-4, tabb...@gmail.com wrote:

On Friday, 11 October 2019 00:20:21 UTC+1, Michael Terrell wrote:
On Thursday, October 10, 2019 at 5:34:08 PM UTC-4, Don Kuenz wrote:
Michael Terrell wrote:
On Thursday, October 10, 2019 at 1:27:04 PM UTC-4, tabb...@gmail.com wrote:

80 is a lotta bucks for claimed 200kHz, real 80kHz. You could get a vintage
real 2 channel scope for that.

It does have an X/Y mode, though. Maybe it could be used to make a handheld
curve tracer.

It turns out that they still sell this /single channel/ DSO for $39:

https://accudiy.com/collections/kits-oscilloscope/products/dso-shell-dso150-oscilloscope-diy-kit

I had looked at that. You need at least two inputs and X/Y mode for a curve tracer.

There are several variants of the DSO138 things out now. They have their uses but bandwidth is firmly in the court jester ballpark. There's one claiming 20MHz that can manage about 2MHz iirc.

Still, they are better that the un-triggered hobby scopes of the past. OK, for some limited uses, but not for most tasks. My first scope was an EICO 460. It was barely useful for Audio.

 

>Yes, I should have stated I'm carrying out these tests at the >very lowest sweep speeds, so slow it's effectively DC. Sorry for >that omission.

You seem to do that quite a bit. Like right now. You do not say exactly what you want to do. Are you trying to use a scope amp for something else or are you trying to cobble up your own scope amp ?

It does make a difference. Now YOU talk of the frequencies being low and we still don't know.

You seem to be the type who would come in here, say "I am building a 100 watt amp, what transistors should I use ? We are supposed to read your fucking mind about all the other parameters. Well that ain't easy and you ain't making it any easier. Go look at my questions here. Some of them are stupid, which Phil will tell you because that is his function here, to call people on his stupidity. We could have all ignored him but we understand. You are not asking in basics, you are asking in design.

When i ask a question I give as many details as possible, except for the very few things I do not want to reveal. There is one thing that before I get into it I want an NDA. We are really talking about alot of money here. We are not talking about some dumb hobbyists shit.

So you can use a scope amp for something else, but why ? First of all if you want real flexibility you need to just use the output and that means youo have to feed it right, that means frequency and phase corrected, as well as SOMETIMES tialored to the CRT which may mean some non-linearity you might not even be able to see on another scope, and VERY rarely some tracking to give it some dynamic focus with the plates. I have only seen that once. In forty years, ONCE. but still you are talking a differential amp with an output impedance so high it can almost run nothing.

And if you want to build the shit and drive the CRT yourself, WHY ?

This is DESIGN. Phil, and I actually, we are just good enough to be here. the thing about design is to get the job done PROPERLY with the minimum time and materials. Now if you are a rich kid who happens to have 37,000 MJE3055s and 2955s in one of your 15 garages alongside your Mazerati and that Cadillac that used to belong to Elvis, fucking say so. Here, the assumption is you want to either DO something or learn something. But if it is simple shit it belongs in basics.

You ask about the load of CRT deflection plates ? I knew that when I was about 12 years old. There is no resistance, the load for the bias of the outputs is handled on the board. With higher bandwidths it may differ. When it come to high performance, like if you want a regular CRT with no digitizing to do 300MHz it takes a bit more. They might have four terminals for the vertical plates. The output of the amps, kinda open collector goes to one set of connections and the collector load resistors goes to the other two. This is because it is like propagation line. something like that. I do not understand it 100%, and I have no desire to sit here and try to explain it to someone who asks what you ask, especially the way you ask it. Even if I knew how every little electron moved in there, which I don't, I would not attempt to explain it because you would never understand it.

I am not pissed off but I am wasting my time telling you why I am not going to waste my time.

Out with it, if you want anything useful here you tell the purpose. The only exceptions are people with secrets, like working on military jobs, undeveloped technologies, trade secrets not ready to be published and under an NDA. I'm guessing you're not.