Likely impedence of this scenario?

Cursitor Doom · Oct 7, 2019

Gentlemen,

Can someone guestimate the likely z between the horizontal deflection
plates of a CRO? The maximum PD between them from the sawtooth gen board
is approx 130V according to the schematic. Can I get away with assuming
this is entirely electrostatic and negligible current flows? I'm planning
to use a 1.2Meg 1/8W resistor as the load for the purposes of testing;
just wondered if that's in the right sort of ballpark?

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Phil Allison · Oct 7, 2019

Cursitor Doom wrote:

------------------------

Gentlemen,

** You are joking ??

Can someone guestimate the likely z between the horizontal deflection
plates of a CRO?

** A few pF of capactance - eg:

https://frank.pocnet.net/sheets/159/d/D14-280GH.pdf

Fromm plates X1 to X2 = 6pF

The maximum PD between them from the sawtooth gen board
is approx 130V according to the schematic. Can I get away with assuming
this is entirely electrostatic and negligible current flows? I'm planning
to use a 1.2Meg 1/8W resistor as the load for the purposes of testing;
just wondered if that's in the right sort of ballpark?

** Doubt it.

Gotta know the frequencies involved first.

..... Phil

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Winfield Hill · Oct 7, 2019

Cursitor Doom wrote...

Can someone guestimate the likely z between the
horizontal deflection plates of a CRO?

Resistive: infinite. Capacitive: "x" pF.

--
Thanks,
- Win

Cursitor Doom · Oct 7, 2019

On Sun, 06 Oct 2019 17:48:57 -0700, Winfield Hill wrote:

Cursitor Doom wrote...

Can someone guestimate the likely z between the horizontal deflection
plates of a CRO?

Resistive: infinite. Capacitive: "x" pF.

Thanks, Win.

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This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
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Winfield Hill · Oct 7, 2019

Cursitor Doom wrote...

On 06 Oct 2019, Winfield Hill wrote:

Cursitor Doom wrote...

Can someone guestimate the likely z between
the horizontal deflection plates of a CRO?

Resistive: infinite. Capacitive: "x" pF.

Thanks, Win.

Phil gave a capacitance value, 6pF. That's a
reasonable typical value. The big deal in the
old days, but not too old, when high-resolution
CRT video monitors were all that rage, like my
$2k Sony monitor, was: maximum current through
video output transistors, and minimum output
capacitance: High Ic for low-value collector
resistors, with low Ccb, to get fast response.
Alibaba has parts from that era, that I use to
make fast high-voltage amplifiers, see AMP-70A:
Not an easy combination. E.g., the KSC2682 was
rated 180V and 8 watts, but Cob was only 3.2pF.
KSC3503: 300V, 7W, 2.6pF and FOM = Pd/Cob = 2.46.
There were npn/pnp pairs, for EF-output stages,
able to handle even higher plate capacitances.

https://www.dropbox.com/s/suog3wy5f1rfskt/AMP-70A-2.pdf?dl=1

If you want all the info in a firehose:

https://www.dropbox.com/sh/dno89om1uezxs8a/AACoJsLyNazSQZvE9_cTcH4Ja?dl=1

--
Thanks,
- Win

Jan Panteltje · Oct 7, 2019

On a sunny day (Mon, 7 Oct 2019 00:02:09 -0000 (UTC)) it happened Cursitor
Doom <curd@notformail.com> wrote in <qndva1$455$1@dont-email.me>:

Gentlemen,

Can someone guestimate the likely z between the horizontal deflection
plates of a CRO? The maximum PD between them from the sawtooth gen board
is approx 130V according to the schematic. Can I get away with assuming
this is entirely electrostatic and negligible current flows? I'm planning
to use a 1.2Meg 1/8W resistor as the load for the purposes of testing;
just wondered if that's in the right sort of ballpark?

Depends on 'speed'.

Basically it is a capacitor (few pF),
but some scopes had a construction of deflection plates that looked more like a transmission line.
Look up the CRT and get the datasheet.
At 300 MHz everything matters including the leads to the defection plates,
some Teks were fine calibrated by bending those a bit.

So for HF it is a complex impedance.

For DC AFAIK no current flows UNLESS you put on such a high voltage that the electron beam hits the plates,

1.2 M is a much too high value look up time constant 100 pF at 1 M is about 10e-10 * 10e6 = 10e-4
or abour 10 kHz........

Not even audio...

50 Ohm and a BFY90 is better.

Winfield Hill · Oct 8, 2019

Jan Panteltje wrote...

50 Ohm and a BFY90 is better.

BFY90 ?

--
Thanks,
- Win

Gerhard Hoffmann · Oct 8, 2019

Am 08.10.19 um 13:44 schrieb Winfield Hill:

Jan Panteltje wrote...

50 Ohm and a BFY90 is better.

BFY90 ?

used to be the VHF NPN in Europe for quality applications.
Including metal case with shield connection.

regards, Gerhard

Cursitor Doom · Oct 9, 2019

On Mon, 07 Oct 2019 06:10:48 +0000, Jan Panteltje wrote:

> Depends on 'speed'.

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.

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Winfield Hill · Oct 9, 2019

Gerhard Hoffmann wrote...

vAm 08.10.19 um 13:44 schrieb Winfield Hill:
Jan Panteltje wrote...

50 Ohm and a BFY90 is better.

BFY90 ?

used to be the VHF NPN in Europe for quality applications.
Including metal case with shield connection.

Yes, I know, how does that work for wideband HV video?

--
Thanks,
- Win

Oct 9, 2019

On Tuesday, 8 October 2019 23:48:30 UTC+1, Cursitor Doom wrote:

On Mon, 07 Oct 2019 06:10:48 +0000, Jan Panteltje wrote:

Depends on 'speed'.

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.

infinite z then

Sort of.

NT

Cursitor Doom · Oct 10, 2019

On Wed, 09 Oct 2019 11:56:36 -0700, tabbypurr wrote:

> infinite z then

Sort of.

Well, quite.

I think the 1.2Meg resistor should take care of it; just really only need
something to very lightly load the outputs to *something* real at least.

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Jan Panteltje · Oct 10, 2019

On a sunny day (Wed, 9 Oct 2019 23:30:33 -0000 (UTC)) it happened Cursitor
Doom <curd@notformail.com> wrote in <qnlqip$8ol$1@dont-email.me>:

On Wed, 09 Oct 2019 11:56:36 -0700, tabbypurr wrote:

infinite z then Sort of.

Well, quite.

I think the 1.2Meg resistor should take care of it; just really only need
something to very lightly load the outputs to *something* real at least.

remember that for a scope horizontal scan the waveform is a sawtooth,
the flyback part of that sawtooth is usually very fast.
Then again it is the deflection plates capacitance + the capacitance of your driver stage
that matters.

You also need trace suppression (cut off CRT beam) during that flyback,
else you get a curved extra trace.

For very slow things I would not bother with a CRT,
just use a micro and some LCD..
http://panteltje.com/panteltje/pic/scope_pic/
China now sells scopes with a micro for < 40$ I think...

But for playing to get understanding CRTs are cool,
you could use magnetic deflection too

My first scope was a TV CRT

HV with a car ignition coil on the output of an audio amp, magnetic deflection...

Personal accelerator

Don Kuenz · Oct 10, 2019

Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Wed, 9 Oct 2019 23:30:33 -0000 (UTC)) it happened Cursitor
Doom <curd@notformail.com> wrote in <qnlqip$8ol$1@dont-email.me>:

On Wed, 09 Oct 2019 11:56:36 -0700, tabbypurr wrote:

infinite z then Sort of.

Well, quite.

I think the 1.2Meg resistor should take care of it; just really only need
something to very lightly load the outputs to *something* real at least.

remember that for a scope horizontal scan the waveform is a sawtooth,
the flyback part of that sawtooth is usually very fast.
Then again it is the deflection plates capacitance + the capacitance of your driver stage
that matters.

You also need trace suppression (cut off CRT beam) during that flyback,
else you get a curved extra trace.

For very slow things I would not bother with a CRT,
just use a micro and some LCD..
http://panteltje.com/panteltje/pic/scope_pic/
China now sells scopes with a micro for < 40$ I think...

But for playing to get understanding CRTs are cool,
you could use magnetic deflection too
My first scope was a TV CRT
HV with a car ignition coil on the output of an audio amp, magnetic deflection...

Personal accelerator

That's a good, informative webpage, Jan. You, Miles, and a few others
inspired me to "grow" my own like minded website.
A while ago a single channel JYE DSO was purchased by me. Peers
advised me to purchase it directly from JYE. It seems that in the
interim since my purchase, JYE evolved its entry level DSO into
2-Channels:

https://accudiy.com/products/wave2-2-channel-oscilloscope

Thank you, 73,

--
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

Oct 10, 2019

On Thursday, 10 October 2019 15:28:31 UTC+1, Don Kuenz wrote:

Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote:
On a sunny day (Wed, 9 Oct 2019 23:30:33 -0000 (UTC)) it happened Cursitor
Doom <curd@notformail.com> wrote in <qnlqip$8ol$1@dont-email.me>:
On Wed, 09 Oct 2019 11:56:36 -0700, tabbypurr wrote:

infinite z then Sort of.

Well, quite.

I think the 1.2Meg resistor should take care of it; just really only need
something to very lightly load the outputs to *something* real at least.

remember that for a scope horizontal scan the waveform is a sawtooth,
the flyback part of that sawtooth is usually very fast.
Then again it is the deflection plates capacitance + the capacitance of your driver stage
that matters.

You also need trace suppression (cut off CRT beam) during that flyback,
else you get a curved extra trace.

For very slow things I would not bother with a CRT,
just use a micro and some LCD..
http://panteltje.com/panteltje/pic/scope_pic/
China now sells scopes with a micro for < 40$ I think...

But for playing to get understanding CRTs are cool,
you could use magnetic deflection too
My first scope was a TV CRT
HV with a car ignition coil on the output of an audio amp, magnetic deflection...

Personal accelerator

That's a good, informative webpage, Jan. You, Miles, and a few others
inspired me to "grow" my own like minded website.
A while ago a single channel JYE DSO was purchased by me. Peers
advised me to purchase it directly from JYE. It seems that in the
interim since my purchase, JYE evolved its entry level DSO into
2-Channels:

https://accudiy.com/products/wave2-2-channel-oscilloscope

Thank you, 73,

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

NT

Oct 10, 2019

tabbypurr@gmail.com wrote in
news:7b7ec1ef-ff7b-4280-ad14-3bbf76970a78@googlegroups.com:

On Thursday, 10 October 2019 15:28:31 UTC+1, Don Kuenz wrote:
Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote:
On a sunny day (Wed, 9 Oct 2019 23:30:33 -0000 (UTC)) it
happened Cursitor Doom <curd@notformail.com> wrote in
qnlqip$8ol$1@dont-email.me>:
On Wed, 09 Oct 2019 11:56:36 -0700, tabbypurr wrote:

infinite z then Sort of.

Well, quite.

I think the 1.2Meg resistor should take care of it; just really
only need something to very lightly load the outputs to
*something* real at least.

remember that for a scope horizontal scan the waveform is a
sawtooth, the flyback part of that sawtooth is usually very
fast. Then again it is the deflection plates capacitance + the
capacitance of your driver stage that matters.

You also need trace suppression (cut off CRT beam) during that
flyback, else you get a curved extra trace.

For very slow things I would not bother with a CRT,
just use a micro and some LCD..
http://panteltje.com/panteltje/pic/scope_pic/
China now sells scopes with a micro for < 40$ I think...

But for playing to get understanding CRTs are cool,
you could use magnetic deflection too
My first scope was a TV CRT
HV with a car ignition coil on the output of an audio amp,
magnetic deflection...

Personal accelerator

That's a good, informative webpage, Jan. You, Miles, and a few
others inspired me to "grow" my own like minded website.
A while ago a single channel JYE DSO was purchased by me.
Peers
advised me to purchase it directly from JYE. It seems that in the
interim since my purchase, JYE evolved its entry level DSO into
2-Channels:

https://accudiy.com/products/wave2-2-channel-oscilloscope

Thank you, 73,

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

NT

Better off getting a USB scope and using your laptop or PC for the
display.

Michael Terrell · Oct 10, 2019

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.

NT

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

Don Kuenz · Oct 10, 2019

Michael Terrell <terrell.michael.a@gmail.com> 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

Thank you, 73,

--
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

Michael Terrell · Oct 11, 2019

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.

Oct 11, 2019

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.

NT

Likely impedence of this scenario?

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