Chip with simple program for Toy

[Jon Slaughter]

<silusilusilu@gmail.com> wrote in message
news:b83fc31e-1383-4a66-931e-58fe1917ab7f@d45g2000hsc.googlegroups.com...
If i consider the open loop gain of an opamp with negative feedback
composed of 2 poles (with negative real part) and one zero (with
positive real part) and if i want a phase margin of 45°, from its
definition
360°-tan^-1[-A(jwo)F(jwo)]=45°
i have
+180°-tan^-1[A(jwo)F(jwo)]=+180°-[-tan^-1(w/p1)-tan^-1(w/p2) -tan^-1(w/
z)]=45°
where +180 is obtained from 360°-tan^-1[negative constant]=360°-
tan^-1[-1]=360°-180°
Instead i've found as solution
+-180°-tan^-1(w/p1)-tan^-1(w/p2) -tan^-1(w/z) =45°
what's wrong?
thanks
=================

wtf is all that?

maybe rewrite them using better notation tan^-1 is also known as arctan,
A(jwo) looks like a function such as f(x) and jwo looks like a single
object.

Also define all your symbols so it will be easier to decipher.


in anycase maybe http://www.intersil.com/data/an/an9415.pdf will help

 

[Kevin Aylward]

lionelgreenstreet@gmail.com wrote:

Thanks for the answer...

Now, knowing that ro of m4 and ro of m2 are in parallel, and the
expression for ro, you should be now able to calcualte the
instantaenous Ro at Vx, as the current is M2 and M2 varied.

Why are m4 and m2 in parallel?

er...well approximatly. Technically m2 source connects through the 1/gm of
m1 to ground

In large signal analysis i should
consider also Vdd (in small signal analysis instead Vdd is signal-
ground, so m4 and m2 are in parallel)... or not?

Only changes need to be considered. Vdd don't change. Technically there is a
"DC resistance" of (Vdd- Vdrain)/ID, but this doesn't really have much
relevance to calculating the "large signal" gain. As I noted, even if Vx
changes a few volts, ro is still the same as its small signal value for
light loads. If you take a lot of current such that this is no longer true,
the stage wont work well, or at all. A lowish resistive load will kill the
gain. Tyically, this stage drives a pmos.

Kevin Aylward

www.anasoft.co.uk
SuperSpice

 

[Andrew Holme]

"Jon Slaughter" <Jon_Slaughter@Hotmail.com> wrote in message
news:2umyk.81$YU2.3@nlpi066.nbdc.sbc.com...

silusilusilu@gmail.com> wrote in message
news:b83fc31e-1383-4a66-931e-58fe1917ab7f@d45g2000hsc.googlegroups.com...
If i consider the open loop gain of an opamp with negative feedback
composed of 2 poles (with negative real part) and one zero (with
positive real part) and if i want a phase margin of 45°, from its
definition
360°-tan^-1[-A(jwo)F(jwo)]=45°
i have
+180°-tan^-1[A(jwo)F(jwo)]=+180°-[-tan^-1(w/p1)-tan^-1(w/p2) -tan^-1(w/
z)]=45°
where +180 is obtained from 360°-tan^-1[negative constant]=360°-
tan^-1[-1]=360°-180°

This appears to say:

360 - arctan(-k) = 360 - arctan(-1) = 360 - 180 = 180

Surely arctan(-1) = -45 and arctan(-k) <> arctan(-1) unless k=1

No?

 

[Michael Robinson]

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:uM6dndsBlukiSlTVnZ2dnUVZ_q3inZ2d@web-ster.com...

jalbers@bsu.edu wrote:
I would like to know how to modify the diode equation: I = Io (Exp(eV/
NkT)-1) to work for a germanium diode. Using Io=10E-12, e=1.602E-19,
T=295, N=1, and k=1.380E-23 has the correct knee 0.6 for a silicon
diode. What needs to be changed (or is there a new equation) to move
the knee back to around 0.3 to model a germanium diode?

Any help would be greatly appreciated. Thanks

Here's one more for all the contradictory advise:

Increase Io. Dramatically.

Perhaps take some measurements of the diode voltage at several different
current values (i.e. 1uA if you can get that low, 10uA, 100uA, 1mA --
don't exceed the diode ratings). Then do a curve fit on semilog paper --
figure that you are going to see Io e^(eV/NkT) only, the "- 1" part will
drop right out.

--

Tim Wescott

Yes, go the empirical route. You can use ordinary graph paper if you want,
by graphing log I versus V, or by graphing I versus exp(V). The -1 drops
out to insignificance, as Tim says. You will find that the data points lie
on a very straight line, until self-heating kicks in, whereupon the graph
will start to curve away from the straight line established at low currents
(constant temperature) where you see the purely exponential side of the
relationship. For small diodes I agree with Tim's suggested current range.

You will have to take more than three measurements if you want to see just
where the curve diverges from the ideal, as a result of self-heating
effects.
Try it. I was pretty impressed at how precisely nature mirrors the math.

 

[christofire]

"goldenhound" <goldenhound104@gmail.com> wrote in message
news:fe75cc7f-42fd-4752-bea5-90b51b935dc9@r15g2000prh.googlegroups.com...

I've built some kits, and can use a soldering iron, but know almost
nothing about trying to troubleshoot a battery-powered electric guitar
effect. Its an Electro Harmonix Electric Mistress Flanger, and it
consists of about two dozen components. I can find where the power
source connects to the board. I hit the first IC and I don't get a
signal, but am I doing it right? How do I test it?

I built a signal probe. I plug a CD player into the "guitar in", and
touch the probe to the PCB trace (which connects to an audio
amplifier), and the music comes out of the amp if I'm following the
trace correctly. Will that help me find the bad component?

1. I should be able to trace power, no?

2. How do you follow a trace on a PCB when it hits an IC or cap or
resistor? Do you have to disconnect it or ?

Whats a good reference for troubleshooting PCB boards and circuits?
Either on the web or in a book?

TIA mucho,
Rob

I expect you'll get lots of suggestions from other users of this NG, some
helpful perhaps. My contribution is:

(a) get the schematic of the model you are working on from the web (e.g.
http://www.diystompboxes.com/pedals/EHmistress_deluxe.jpg) and, if you need
to, data sheet(s) for the semiconductors used (e.g. for the SAD1024 in this
case)

(b) figure out how the circuit works from the schematic and the data
sheet(s), and therefore what kinds of signal or other voltage should be
found at different points (i.e. junctions) in the circuit

(c) correlate components in the schematic with components on the PCB and
then you'll know what you should find by probing the PCB - you'll also
answer your own first two questions

A bright lamp is useful for following tracks on a single-sided PCB; perhaps
even a double-sided one if it doesn't have expanses of ground plane.

Good luck,

Chris

 

[ian field]

"Dan Beck" <biscuitbecks@*nospam*cableone.net> wrote in message
news:gagld5$erd$1@registered.motzarella.org...

Hello all,

years ago I was given a 10 MHz Heathkit oscilloscope. Both channels work
fine, and I use it to probe circuit boards powered up on the workbench. I
now own an old hobby car with the old fashioned plugs/points/capacitor
ignition. Is there any way I could use the 'scope to observe the ignition
signals, and would there be any value to it, besides academic information?

Thank you in advance for any and all thoughts!

Regards,
Dan

The LT back emf could spike as high as 600V (maybe even higher) if the scope
is all tube you should be OK, but if it uses transistors in the Y amplifiers
some caution might be wise. Study the spec for the x10 probe and if it isn't
rated for that voltage then make a voltage divider yourself, here again you
need to check the voltage rating of the resistors - if necessary make the
dropper section of the divider out of a number of series resistors.

 

[christofire]

"goldenhound" <goldenhound104@gmail.com> wrote in message
news:fe75cc7f-42fd-4752-bea5-90b51b935dc9@r15g2000prh.googlegroups.com...

I've built some kits, and can use a soldering iron, but know almost
nothing about trying to troubleshoot a battery-powered electric guitar
effect. Its an Electro Harmonix Electric Mistress Flanger, and it
consists of about two dozen components. I can find where the power
source connects to the board. I hit the first IC and I don't get a
signal, but am I doing it right? How do I test it?

I built a signal probe. I plug a CD player into the "guitar in", and
touch the probe to the PCB trace (which connects to an audio
amplifier), and the music comes out of the amp if I'm following the
trace correctly. Will that help me find the bad component?

1. I should be able to trace power, no?

2. How do you follow a trace on a PCB when it hits an IC or cap or
resistor? Do you have to disconnect it or ?

Whats a good reference for troubleshooting PCB boards and circuits?
Either on the web or in a book?

TIA mucho,
Rob

I expect you'll get lots of suggestions from other users of this NG, some
helpful perhaps. My contribution is:

(a) get the schematic of the model you are working on from the web (e.g.
http://www.diystompboxes.com/pedals/EHmistress_deluxe.jpg) and, if you need
to, data sheet(s) for the semiconductors used (e.g. for the SAD1024 in this
case)

(b) figure out how the circuit works from the schematic and the data
sheet(s), and therefore what kinds of signal or other voltage should be
found at different points (i.e. junctions) in the circuit

(c) correlate components in the schematic with components on the PCB and
then you'll know what you should find by probing the PCB - you'll also
answer your own first two questions

A bright lamp is useful for following tracks on a single-sided PCB; perhaps
even a double-sided one if it doesn't have expanses of ground plane.

Good luck,

Chris

 

[ian field]

"Dan Beck" <biscuitbecks@*nospam*cableone.net> wrote in message
news:gagld5$erd$1@registered.motzarella.org...

Hello all,

years ago I was given a 10 MHz Heathkit oscilloscope. Both channels work
fine, and I use it to probe circuit boards powered up on the workbench. I
now own an old hobby car with the old fashioned plugs/points/capacitor
ignition. Is there any way I could use the 'scope to observe the ignition
signals, and would there be any value to it, besides academic information?

Thank you in advance for any and all thoughts!

Regards,
Dan

The LT back emf could spike as high as 600V (maybe even higher) if the scope
is all tube you should be OK, but if it uses transistors in the Y amplifiers
some caution might be wise. Study the spec for the x10 probe and if it isn't
rated for that voltage then make a voltage divider yourself, here again you
need to check the voltage rating of the resistors - if necessary make the
dropper section of the divider out of a number of series resistors.

 

[christofire]

"goldenhound" <goldenhound104@gmail.com> wrote in message
news:fe75cc7f-42fd-4752-bea5-90b51b935dc9@r15g2000prh.googlegroups.com...

I've built some kits, and can use a soldering iron, but know almost
nothing about trying to troubleshoot a battery-powered electric guitar
effect. Its an Electro Harmonix Electric Mistress Flanger, and it
consists of about two dozen components. I can find where the power
source connects to the board. I hit the first IC and I don't get a
signal, but am I doing it right? How do I test it?

I built a signal probe. I plug a CD player into the "guitar in", and
touch the probe to the PCB trace (which connects to an audio
amplifier), and the music comes out of the amp if I'm following the
trace correctly. Will that help me find the bad component?

1. I should be able to trace power, no?

2. How do you follow a trace on a PCB when it hits an IC or cap or
resistor? Do you have to disconnect it or ?

Whats a good reference for troubleshooting PCB boards and circuits?
Either on the web or in a book?

TIA mucho,
Rob

I expect you'll get lots of suggestions from other users of this NG, some
helpful perhaps. My contribution is:

(a) get the schematic of the model you are working on from the web (e.g.
http://www.diystompboxes.com/pedals/EHmistress_deluxe.jpg) and, if you need
to, data sheet(s) for the semiconductors used (e.g. for the SAD1024 in this
case)

(b) figure out how the circuit works from the schematic and the data
sheet(s), and therefore what kinds of signal or other voltage should be
found at different points (i.e. junctions) in the circuit

(c) correlate components in the schematic with components on the PCB and
then you'll know what you should find by probing the PCB - you'll also
answer your own first two questions

A bright lamp is useful for following tracks on a single-sided PCB; perhaps
even a double-sided one if it doesn't have expanses of ground plane.

Good luck,

Chris

 

[ian field]

"Dan Beck" <biscuitbecks@*nospam*cableone.net> wrote in message
news:gagld5$erd$1@registered.motzarella.org...

Hello all,

years ago I was given a 10 MHz Heathkit oscilloscope. Both channels work
fine, and I use it to probe circuit boards powered up on the workbench. I
now own an old hobby car with the old fashioned plugs/points/capacitor
ignition. Is there any way I could use the 'scope to observe the ignition
signals, and would there be any value to it, besides academic information?

Thank you in advance for any and all thoughts!

Regards,
Dan

The LT back emf could spike as high as 600V (maybe even higher) if the scope
is all tube you should be OK, but if it uses transistors in the Y amplifiers
some caution might be wise. Study the spec for the x10 probe and if it isn't
rated for that voltage then make a voltage divider yourself, here again you
need to check the voltage rating of the resistors - if necessary make the
dropper section of the divider out of a number of series resistors.

 

[christofire]

"goldenhound" <goldenhound104@gmail.com> wrote in message
news:fe75cc7f-42fd-4752-bea5-90b51b935dc9@r15g2000prh.googlegroups.com...

I've built some kits, and can use a soldering iron, but know almost
nothing about trying to troubleshoot a battery-powered electric guitar
effect. Its an Electro Harmonix Electric Mistress Flanger, and it
consists of about two dozen components. I can find where the power
source connects to the board. I hit the first IC and I don't get a
signal, but am I doing it right? How do I test it?

I built a signal probe. I plug a CD player into the "guitar in", and
touch the probe to the PCB trace (which connects to an audio
amplifier), and the music comes out of the amp if I'm following the
trace correctly. Will that help me find the bad component?

1. I should be able to trace power, no?

2. How do you follow a trace on a PCB when it hits an IC or cap or
resistor? Do you have to disconnect it or ?

Whats a good reference for troubleshooting PCB boards and circuits?
Either on the web or in a book?

TIA mucho,
Rob

I expect you'll get lots of suggestions from other users of this NG, some
helpful perhaps. My contribution is:

(a) get the schematic of the model you are working on from the web (e.g.
http://www.diystompboxes.com/pedals/EHmistress_deluxe.jpg) and, if you need
to, data sheet(s) for the semiconductors used (e.g. for the SAD1024 in this
case)

(b) figure out how the circuit works from the schematic and the data
sheet(s), and therefore what kinds of signal or other voltage should be
found at different points (i.e. junctions) in the circuit

(c) correlate components in the schematic with components on the PCB and
then you'll know what you should find by probing the PCB - you'll also
answer your own first two questions

A bright lamp is useful for following tracks on a single-sided PCB; perhaps
even a double-sided one if it doesn't have expanses of ground plane.

Good luck,

Chris

 

[ian field]

"Dan Beck" <biscuitbecks@*nospam*cableone.net> wrote in message
news:gagld5$erd$1@registered.motzarella.org...

Hello all,

years ago I was given a 10 MHz Heathkit oscilloscope. Both channels work
fine, and I use it to probe circuit boards powered up on the workbench. I
now own an old hobby car with the old fashioned plugs/points/capacitor
ignition. Is there any way I could use the 'scope to observe the ignition
signals, and would there be any value to it, besides academic information?

Thank you in advance for any and all thoughts!

Regards,
Dan

The LT back emf could spike as high as 600V (maybe even higher) if the scope
is all tube you should be OK, but if it uses transistors in the Y amplifiers
some caution might be wise. Study the spec for the x10 probe and if it isn't
rated for that voltage then make a voltage divider yourself, here again you
need to check the voltage rating of the resistors - if necessary make the
dropper section of the divider out of a number of series resistors.

 

[Jon Slaughter]

"goldenhound" <goldenhound104@gmail.com> wrote in message
news:fe75cc7f-42fd-4752-bea5-90b51b935dc9@r15g2000prh.googlegroups.com...

I've built some kits, and can use a soldering iron, but know almost
nothing about trying to troubleshoot a battery-powered electric guitar
effect. Its an Electro Harmonix Electric Mistress Flanger, and it
consists of about two dozen components. I can find where the power
source connects to the board. I hit the first IC and I don't get a
signal, but am I doing it right? How do I test it?

I built a signal probe. I plug a CD player into the "guitar in", and
touch the probe to the PCB trace (which connects to an audio
amplifier), and the music comes out of the amp if I'm following the
trace correctly. Will that help me find the bad component?

it might... I guess better than nothing.

1. I should be able to trace power, no?

2. How do you follow a trace on a PCB when it hits an IC or cap or
resistor? Do you have to disconnect it or ?

you have to know what the ic does. It has inputs and outputs... to follow a
passive component you just "go through" the component. (same thing sorta
happens inside the ic but its extremely complex and you don't know the
"connections" so you have to know the macro function)

Whats a good reference for troubleshooting PCB boards and circuits?
Either on the web or in a book?

TIA mucho,
Rob

First look for the obivous. Any burned components or burnt smell? Any broken
wires or traces or loose components?

Look at what is happen? No power? No sound? Distorted sound, etc...

Look at the input, output and power stages. This are the ons likely to go
first. Components such as resistors and capacitors rarely go back so they
can be ignored at first(although if they do go bad and it's not obvious it
can be very frustrating figure it out). Digital logic also rarely goes bad.

Thing's like diodes, transistors, regulators, op amps, etc.. are the first
bet.

The main thing is to test power.. because it is the easiest and obviously if
it's not getting power your not going to get anywhere and this is really the
place that gets screwed the most(people trying to power it with different
voltage than it's rated for).

In fact I'd test the power pin of all the IC's starting with the power stage
and at the same time test the diodes(which you can try to do in circuit but
doesn't always work but might lead to a quick answer).

What you'll probably find is that either the power stage or discrete
transistors are bad but it could be something as simple as the input or
output comming loose or a connection breaking do to wear.

 

[Jon Slaughter]

"goldenhound" <goldenhound104@gmail.com> wrote in message
news:fe75cc7f-42fd-4752-bea5-90b51b935dc9@r15g2000prh.googlegroups.com...

I've built some kits, and can use a soldering iron, but know almost
nothing about trying to troubleshoot a battery-powered electric guitar
effect. Its an Electro Harmonix Electric Mistress Flanger, and it
consists of about two dozen components. I can find where the power
source connects to the board. I hit the first IC and I don't get a
signal, but am I doing it right? How do I test it?

I built a signal probe. I plug a CD player into the "guitar in", and
touch the probe to the PCB trace (which connects to an audio
amplifier), and the music comes out of the amp if I'm following the
trace correctly. Will that help me find the bad component?

it might... I guess better than nothing.

1. I should be able to trace power, no?

2. How do you follow a trace on a PCB when it hits an IC or cap or
resistor? Do you have to disconnect it or ?

you have to know what the ic does. It has inputs and outputs... to follow a
passive component you just "go through" the component. (same thing sorta
happens inside the ic but its extremely complex and you don't know the
"connections" so you have to know the macro function)

Whats a good reference for troubleshooting PCB boards and circuits?
Either on the web or in a book?

TIA mucho,
Rob

First look for the obivous. Any burned components or burnt smell? Any broken
wires or traces or loose components?

Look at what is happen? No power? No sound? Distorted sound, etc...

Look at the input, output and power stages. This are the ons likely to go
first. Components such as resistors and capacitors rarely go back so they
can be ignored at first(although if they do go bad and it's not obvious it
can be very frustrating figure it out). Digital logic also rarely goes bad.

Thing's like diodes, transistors, regulators, op amps, etc.. are the first
bet.

The main thing is to test power.. because it is the easiest and obviously if
it's not getting power your not going to get anywhere and this is really the
place that gets screwed the most(people trying to power it with different
voltage than it's rated for).

In fact I'd test the power pin of all the IC's starting with the power stage
and at the same time test the diodes(which you can try to do in circuit but
doesn't always work but might lead to a quick answer).

What you'll probably find is that either the power stage or discrete
transistors are bad but it could be something as simple as the input or
output comming loose or a connection breaking do to wear.

 

[Jon Slaughter]

"goldenhound" <goldenhound104@gmail.com> wrote in message
news:fe75cc7f-42fd-4752-bea5-90b51b935dc9@r15g2000prh.googlegroups.com...

I've built some kits, and can use a soldering iron, but know almost
nothing about trying to troubleshoot a battery-powered electric guitar
effect. Its an Electro Harmonix Electric Mistress Flanger, and it
consists of about two dozen components. I can find where the power
source connects to the board. I hit the first IC and I don't get a
signal, but am I doing it right? How do I test it?

I built a signal probe. I plug a CD player into the "guitar in", and
touch the probe to the PCB trace (which connects to an audio
amplifier), and the music comes out of the amp if I'm following the
trace correctly. Will that help me find the bad component?

it might... I guess better than nothing.

1. I should be able to trace power, no?

2. How do you follow a trace on a PCB when it hits an IC or cap or
resistor? Do you have to disconnect it or ?

you have to know what the ic does. It has inputs and outputs... to follow a
passive component you just "go through" the component. (same thing sorta
happens inside the ic but its extremely complex and you don't know the
"connections" so you have to know the macro function)

Whats a good reference for troubleshooting PCB boards and circuits?
Either on the web or in a book?

TIA mucho,
Rob

First look for the obivous. Any burned components or burnt smell? Any broken
wires or traces or loose components?

Look at what is happen? No power? No sound? Distorted sound, etc...

Look at the input, output and power stages. This are the ons likely to go
first. Components such as resistors and capacitors rarely go back so they
can be ignored at first(although if they do go bad and it's not obvious it
can be very frustrating figure it out). Digital logic also rarely goes bad.

Thing's like diodes, transistors, regulators, op amps, etc.. are the first
bet.

The main thing is to test power.. because it is the easiest and obviously if
it's not getting power your not going to get anywhere and this is really the
place that gets screwed the most(people trying to power it with different
voltage than it's rated for).

In fact I'd test the power pin of all the IC's starting with the power stage
and at the same time test the diodes(which you can try to do in circuit but
doesn't always work but might lead to a quick answer).

What you'll probably find is that either the power stage or discrete
transistors are bad but it could be something as simple as the input or
output comming loose or a connection breaking do to wear.

 

[ian field]

"Jasen Betts" <jasen@xnet.co.nz> wrote in message news:gaip33$33q$3@gonzo...

On 2008-09-14, Paul E. Schoen <pstech@smart.net> wrote:
It might be prudent to add a neon lamp or a TVS bidirectional zener type
suppressor across the scope inputs. I'm not sure how fast a neon lamp
triggers, but the type of suppressors used in telephone equipment should
be
pretty good, and rated about 60 volts.

at 60 they'd fire on the ring voltage.

Bye.
Jasen

Might not be so bad if the OP builds a scope lead breakout box to add the
neon so it can be shunt connected between a x10 probe and the scope input.

 

[ian field]

"Jasen Betts" <jasen@xnet.co.nz> wrote in message news:gaip33$33q$3@gonzo...

On 2008-09-14, Paul E. Schoen <pstech@smart.net> wrote:
It might be prudent to add a neon lamp or a TVS bidirectional zener type
suppressor across the scope inputs. I'm not sure how fast a neon lamp
triggers, but the type of suppressors used in telephone equipment should
be
pretty good, and rated about 60 volts.

at 60 they'd fire on the ring voltage.

Bye.
Jasen

Might not be so bad if the OP builds a scope lead breakout box to add the
neon so it can be shunt connected between a x10 probe and the scope input.

 

[ian field]

"Jasen Betts" <jasen@xnet.co.nz> wrote in message news:gaip33$33q$3@gonzo...

On 2008-09-14, Paul E. Schoen <pstech@smart.net> wrote:
It might be prudent to add a neon lamp or a TVS bidirectional zener type
suppressor across the scope inputs. I'm not sure how fast a neon lamp
triggers, but the type of suppressors used in telephone equipment should
be
pretty good, and rated about 60 volts.

at 60 they'd fire on the ring voltage.

Bye.
Jasen

Might not be so bad if the OP builds a scope lead breakout box to add the
neon so it can be shunt connected between a x10 probe and the scope input.

 

[ian field]

"Jasen Betts" <jasen@xnet.co.nz> wrote in message news:gaip33$33q$3@gonzo...

On 2008-09-14, Paul E. Schoen <pstech@smart.net> wrote:
It might be prudent to add a neon lamp or a TVS bidirectional zener type
suppressor across the scope inputs. I'm not sure how fast a neon lamp
triggers, but the type of suppressors used in telephone equipment should
be
pretty good, and rated about 60 volts.

at 60 they'd fire on the ring voltage.

Bye.
Jasen

Might not be so bad if the OP builds a scope lead breakout box to add the
neon so it can be shunt connected between a x10 probe and the scope input.

 

[ian field]

"Jasen Betts" <jasen@xnet.co.nz> wrote in message news:gaip33$33q$3@gonzo...

On 2008-09-14, Paul E. Schoen <pstech@smart.net> wrote:
It might be prudent to add a neon lamp or a TVS bidirectional zener type
suppressor across the scope inputs. I'm not sure how fast a neon lamp
triggers, but the type of suppressors used in telephone equipment should
be
pretty good, and rated about 60 volts.

at 60 they'd fire on the ring voltage.

Bye.
Jasen

Might not be so bad if the OP builds a scope lead breakout box to add the
neon so it can be shunt connected between a x10 probe and the scope input.