Date   
Re: HV Probe and DMM Input Impedance

Chuck Harris
 

The 410C has a 200Mohm DC input impedance. Any HV probe
not designed for the 410C will work poorly, if at all.

That said, to use a probe designed for 11M on a higher
impedance meter, you can add a parallel resistance to
bring the meter's impedance to the probe's design value.

Be careful when using any HV probe with an autorange DVM.

Most higher quality DVM's have super high input impedances
on their native input range... typically the lowest voltage
range. If the autorange starts on that range, the meter will
be likely burn out due to the HV surge.

-Chuck Harris

n4buq wrote:

I do have older VTVMs (HP 410B, 410C, etc.) so I could use it with those as well. I have an older HP probe (459A) designed to be used with those (has a different resistor) but it's missing the spring-loaded end-cap as well as has a different resistor value. I took a look at that one yesterday and noticed the resistor has a rather sticky film on it. I wonder if that was originally there to reduce the effect of arcing?

If the resistor in my "new" probe didn't have fingerprints on it before, it does now. I'll be sure to wipe down. Thanks for the tip!

Thanks,
Barry - N4BUQ

Re: 11801 bug fixes

Chuck Harris
 

I presume that you have some of the path I mentioned...

If your "unlettered" scope is truly missing this function,
it is a strong indication that tektronix knew about the
LED's affecting the timing, and added it in as a non-electrical
fix.

-Chuck Harris

Leo Bodnar wrote:

My CSA803 does not have this function.
Leo

On Mon, Oct 28, 2019 at 02:16 PM, Chuck Harris wrote:
Assuming that this isn't exclusively a "C" function:
WAVEFORM
-> SAMPLING HEAD FNC'S
-> SELECTED CHANNEL IDENTIFICATION
-> QUIET


Re: HV Probe and DMM Input Impedance

n4buq
 

I do have older VTVMs (HP 410B, 410C, etc.) so I could use it with those as well. I have an older HP probe (459A) designed to be used with those (has a different resistor) but it's missing the spring-loaded end-cap as well as has a different resistor value. I took a look at that one yesterday and noticed the resistor has a rather sticky film on it. I wonder if that was originally there to reduce the effect of arcing?

If the resistor in my "new" probe didn't have fingerprints on it before, it does now. I'll be sure to wipe down. Thanks for the tip!

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Michael A. Terrell" <@michaelaterrell>
To: TekScopes@groups.io
Sent: Monday, October 28, 2019 9:42:01 AM
Subject: Re: [TekScopes] HV Probe and DMM Input Impedance

That probe was made for a common, TV shop grade VTVM, with a 10M input
impedance, for AC measurements. In DC mode, a 1M resistor at the probe tip
gave a total of 11M impedance. This was done to reduce the input
capacitance which would detune RF stages, or quench an oscillator. This was
critical while servicing the high impedances encountered on tube based
electonics.

Add 1090M to 10M, and you get 1,100M wich is 100 times the impedance with
the HV probe. Be sure there are no fingerprints on the body of that
resistor, or it may arc over under HV use.

On Mon, Oct 28, 2019 at 9:36 AM n4buq <n4buq@...> wrote:

This last weekend, I found an EICO HV probe in very nice condition at an
estate sale. Opening it up, it contiains a 1.09G ohm resistor in series
with the tip and cable. I connected it to the input of my Fluke 27 DMM and
measured a low voltage source (all I had handy at that moment). From what
I could tell, the probe gives me a 100x scale factor (e.g 10VDC measured
0.1VDC). While I may need to measure some higher voltages to confirm
whether this is really accurate, it appears to be at least somewhat
accurate.

I have a question, though, regarding the theory of the way this works.
The Fluke has a 10M ohm input resistance which, if I'm thinking about this
correctly, makes the measuring circuit 1100M ohms of which 10M ohm is the
meter and the remaining resistance in the voltage divider network is the
probe's resistor; however, I'm having trouble with the math.

Intuitively, (for me, at least), to obtain a 1/100 divider, I would think
that ideally the probe resistance should be 0.990M ohms with the meter
providing the remainin 10M ohms. But I find it odd that the resistor has
that odd value which makes it seem like it was almost intended to work with
a 10M device.

If I'm not mistaken, those probes were intended to be used with a
particular device (meter) that provided the proper readings but not sure
about that either (not finding a lot of info on this probe).

Am I off base here? I know that some of the HV probes designed to work
with the Fluke are designed to connect differently and I think the meter is
used in mA mode with them but not sure about that.

Is it a false expectation that the meter give me a 1/100 reading when used
with the probe in that manner? Is it also possible that the 1090M ohm is
giving me a "close enough" with that low voltage test and the difference
would become more measurable with higher voltages?

Sorry - this should be simple but, for some reason, I can't make it make
sense to me at the moment.

Thanks,
Barry - N4BUQ





Re: Tektronix 475 Oscilloscope - Help With Repair

Mlynch001
 

I have visually checked the “glow” of the heater filament on 465B, 468 and 475A over the past few weeks. They are all just barely discernible through that white area in the very center of the rear of the CRT. None of my functional scopes has a “bright” glow. My experience with this series of scopes is that These things just do not glow that bright. Probably to save wear and tear on the filament?

--
Michael Lynch
Dardanelle, AR

Re: 11801 bug fixes

Leo Bodnar
 

My CSA803 does not have this function.
Leo

On Mon, Oct 28, 2019 at 02:16 PM, Chuck Harris wrote:
Assuming that this isn't exclusively a "C" function:
WAVEFORM
-> SAMPLING HEAD FNC'S
-> SELECTED CHANNEL IDENTIFICATION
-> QUIET

Re: HV Probe and DMM Input Impedance

Michael A. Terrell
 

That probe was made for a common, TV shop grade VTVM, with a 10M input
impedance, for AC measurements. In DC mode, a 1M resistor at the probe tip
gave a total of 11M impedance. This was done to reduce the input
capacitance which would detune RF stages, or quench an oscillator. This was
critical while servicing the high impedances encountered on tube based
electonics.

Add 1090M to 10M, and you get 1,100M wich is 100 times the impedance with
the HV probe. Be sure there are no fingerprints on the body of that
resistor, or it may arc over under HV use.

On Mon, Oct 28, 2019 at 9:36 AM n4buq <n4buq@...> wrote:

This last weekend, I found an EICO HV probe in very nice condition at an
estate sale. Opening it up, it contiains a 1.09G ohm resistor in series
with the tip and cable. I connected it to the input of my Fluke 27 DMM and
measured a low voltage source (all I had handy at that moment). From what
I could tell, the probe gives me a 100x scale factor (e.g 10VDC measured
0.1VDC). While I may need to measure some higher voltages to confirm
whether this is really accurate, it appears to be at least somewhat
accurate.

I have a question, though, regarding the theory of the way this works.
The Fluke has a 10M ohm input resistance which, if I'm thinking about this
correctly, makes the measuring circuit 1100M ohms of which 10M ohm is the
meter and the remaining resistance in the voltage divider network is the
probe's resistor; however, I'm having trouble with the math.

Intuitively, (for me, at least), to obtain a 1/100 divider, I would think
that ideally the probe resistance should be 0.990M ohms with the meter
providing the remainin 10M ohms. But I find it odd that the resistor has
that odd value which makes it seem like it was almost intended to work with
a 10M device.

If I'm not mistaken, those probes were intended to be used with a
particular device (meter) that provided the proper readings but not sure
about that either (not finding a lot of info on this probe).

Am I off base here? I know that some of the HV probes designed to work
with the Fluke are designed to connect differently and I think the meter is
used in mA mode with them but not sure about that.

Is it a false expectation that the meter give me a 1/100 reading when used
with the probe in that manner? Is it also possible that the 1090M ohm is
giving me a "close enough" with that low voltage test and the difference
would become more measurable with higher voltages?

Sorry - this should be simple but, for some reason, I can't make it make
sense to me at the moment.

Thanks,
Barry - N4BUQ



Re: HV Probe and DMM Input Impedance

EB4APL
 

Hi,

I have a couple of HV probes, one is a Metrix HT-212 with a 990 MOhm resistor that is intended for 10 MOhm meters, and your math is ok.

The other is an old RCA WG-206, with a 1090 MOhm resistor, just as yours.  These old HV probes were designed to be used with the (then) common VTVM's.

These meters usually have a 10 MOhm input resistance which was complemented with one 1 MOhm resistor inside the normal DC probe, so the VTVM - probe combination have 11 MOhm input resistance. The meter scale was made in such a way to account for this 1 - 10 MOhm resistor divider (10/11 ratio).

If instead a 1MOhm input resistor a HV probe with a 1090 MOhm resiswtor is used, the new input voltage divider is now 1100 - 10 MOhm (10/1100 ratio, 100 times bigger), so the multiplication factor is 100.

I got the RCA probe first, and I had planned so use an adaptation circuit between the probe and the DVM, which had to reduce the ratio to 1000/1, still useful with the sensitivity of normal DVM. In part due to the probe connector was an old microphone connector almost impossible to obtain today at a reasonable price, and the acquisition of the Metrix HV probe, I left the RCA one as is, to mate my Kyoritsu K-142 VTVM.

Best regards,

Ignacio EB4APL

El 28/10/2019 a las 14:47, n4buq escribió:
BTW, this is what the probe looks like:

https://www.etsy.com/hk-en/listing/491393770/eico-high-voltage-uni-probe

Not sure, but it appears the one pictured has a scale factor of 106 (as stated on the home-made label when used with a 10M ohm meter) so maybe that's more the case (e.g. not exactly a 100:1 divider when used that way)?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: TekScopes@groups.io
Sent: Monday, October 28, 2019 8:36:37 AM
Subject: [TekScopes] HV Probe and DMM Input Impedance

This last weekend, I found an EICO HV probe in very nice condition at an
estate sale. Opening it up, it contiains a 1.09G ohm resistor in series
with the tip and cable. I connected it to the input of my Fluke 27 DMM and
measured a low voltage source (all I had handy at that moment). From what I
could tell, the probe gives me a 100x scale factor (e.g 10VDC measured
0.1VDC). While I may need to measure some higher voltages to confirm
whether this is really accurate, it appears to be at least somewhat
accurate.

I have a question, though, regarding the theory of the way this works. The
Fluke has a 10M ohm input resistance which, if I'm thinking about this
correctly, makes the measuring circuit 1100M ohms of which 10M ohm is the
meter and the remaining resistance in the voltage divider network is the
probe's resistor; however, I'm having trouble with the math.

Intuitively, (for me, at least), to obtain a 1/100 divider, I would think
that ideally the probe resistance should be 0.990M ohms with the meter
providing the remainin 10M ohms. But I find it odd that the resistor has
that odd value which makes it seem like it was almost intended to work with
a 10M device.

If I'm not mistaken, those probes were intended to be used with a particular
device (meter) that provided the proper readings but not sure about that
either (not finding a lot of info on this probe).

Am I off base here? I know that some of the HV probes designed to work with
the Fluke are designed to connect differently and I think the meter is used
in mA mode with them but not sure about that.

Is it a false expectation that the meter give me a 1/100 reading when used
with the probe in that manner? Is it also possible that the 1090M ohm is
giving me a "close enough" with that low voltage test and the difference
would become more measurable with higher voltages?

Sorry - this should be simple but, for some reason, I can't make it make
sense to me at the moment.

Thanks,
Barry - N4BUQ




--
El software de antivirus Avast ha analizado este correo electrónico en busca de virus.
https://www.avast.com/antivirus

Re: TDS3044B repair

Oz-in-DFW
 

I'd still remove and reseat both ends.

Where are you in the world? I have a VGA/serial/GPIB card in my 3014 that we might be able to mate with your scope briefly.

Re: HV Probe and DMM Input Impedance

n4buq
 

Hi Jerry,

That's about what I thought but the 1.09G ohm seemed too coincidental and kept bugging me. At the same sale, I bought a new-old-stock-still-in-the-box RCA resistor with that same value but a slightly smaller form-factor. In the box were two 45M ohm and one 25M ohm resistors. It appeared whoever had owned these had done a lot of electronic experimentation as there were several pieces of homemade boxes for things like a transistor testor, etc. I bought a nice inductance substitution box as well.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Jerry Ingordo" <gjingordo@...>
To: TekScopes@groups.io
Sent: Monday, October 28, 2019 9:08:12 AM
Subject: Re: [TekScopes] HV Probe and DMM Input Impedance

These HV probes we designed so that you can replace the series resistor to
match the input resistance of the meter you intend to use with it. As you
know its just a voltage divider. The resistor has to be nine times your
meters input resistance (at the scale you intend to use). So for 10m input
the resistor would be 90M for a X10 probe. I made a resistor once form a
wooden chop stick with end caps from a fuse with series resistors on a lark.
It worked so well I never changed it. I have a few RCA probes along the
lines of the Eico. RCA also sold different resistors to match different
input resistances. I used it many time to check HV on Tek gear.
Jerry
W2JI



Re: Tektronix 475 Oscilloscope - Help With Repair

necromancermi@...
 

It is very hard to see because of all the shielding that is present. From the rear socket in a dark room I can just barely see a faint neck glow. To me from all the CRT's I've worked on the neck glow is much brighter.

Re: 11801 bug fixes

Chuck Harris
 

Hi Leo and David,

Assuming that this isn't exclusively a "C" function:

WAVEFORM
-> SAMPLING HEAD FNC'S
-> SELECTED CHANNEL IDENTIFICATION
-> QUIET

QUIET, as opposed to BLINKING

-Chuck Harris

Leo Bodnar wrote:

Yes. I have removed LED from the head and it stopped bouncing back and forth.
Make sure no other channel LED is blinking as it will affect the traces on all active channels.
I suspect the LED return current upsets TDR drive pulse somewhere.

Chuck, how do you configure LEDs not to blink? I dread to go through all the menus.

Leo

Leo,
Is this really all it takes to fix the LED bug? If so, I might give it a shot.
David

Re: HV Probe and DMM Input Impedance

Jerry Ingordo
 

These HV probes we designed so that you can replace the series resistor to match the input resistance of the meter you intend to use with it. As you know its just a voltage divider. The resistor has to be nine times your meters input resistance (at the scale you intend to use). So for 10m input the resistor would be 90M for a X10 probe. I made a resistor once form a wooden chop stick with end caps from a fuse with series resistors on a lark. It worked so well I never changed it. I have a few RCA probes along the lines of the Eico. RCA also sold different resistors to match different input resistances. I used it many time to check HV on Tek gear.
Jerry
W2JI

Re: LCD screen for CSA803 or 1180x

Reginald Beardsley
 

Looks like a new product Leo. How much?

I've been doing comparisons of connectors and adapters. So I often have stored traces on screen for a considerable period of time and have been worried about screen burn.

The stored traces are lost if I turn the scope off, so I'll leave it running all day with the intensity set to the minimum value.

Re: 11801 bug fixes

Reginald Beardsley
 

Thanks. Much less trouble.

I have Mainframe B030215. Is there a date encoded in that?

Executive processor: 10.09
Display: 9.0
Time base controller: 10.11
Acquisition #1: 9.02
Acquisition #2: 9.02

I see about 5 ps of slow jitter, but it doesn't correlate with the LED blinking. It's much slower, perhaps 30 seconds from one extreme to the other. Though sometimes it will move 2-3 ps in a few seconds.

However, having all the times off by >10x is the biggest issue.

Re: HV Probe and DMM Input Impedance

n4buq
 

BTW, this is what the probe looks like:

https://www.etsy.com/hk-en/listing/491393770/eico-high-voltage-uni-probe

Not sure, but it appears the one pictured has a scale factor of 106 (as stated on the home-made label when used with a 10M ohm meter) so maybe that's more the case (e.g. not exactly a 100:1 divider when used that way)?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: TekScopes@groups.io
Sent: Monday, October 28, 2019 8:36:37 AM
Subject: [TekScopes] HV Probe and DMM Input Impedance

This last weekend, I found an EICO HV probe in very nice condition at an
estate sale. Opening it up, it contiains a 1.09G ohm resistor in series
with the tip and cable. I connected it to the input of my Fluke 27 DMM and
measured a low voltage source (all I had handy at that moment). From what I
could tell, the probe gives me a 100x scale factor (e.g 10VDC measured
0.1VDC). While I may need to measure some higher voltages to confirm
whether this is really accurate, it appears to be at least somewhat
accurate.

I have a question, though, regarding the theory of the way this works. The
Fluke has a 10M ohm input resistance which, if I'm thinking about this
correctly, makes the measuring circuit 1100M ohms of which 10M ohm is the
meter and the remaining resistance in the voltage divider network is the
probe's resistor; however, I'm having trouble with the math.

Intuitively, (for me, at least), to obtain a 1/100 divider, I would think
that ideally the probe resistance should be 0.990M ohms with the meter
providing the remainin 10M ohms. But I find it odd that the resistor has
that odd value which makes it seem like it was almost intended to work with
a 10M device.

If I'm not mistaken, those probes were intended to be used with a particular
device (meter) that provided the proper readings but not sure about that
either (not finding a lot of info on this probe).

Am I off base here? I know that some of the HV probes designed to work with
the Fluke are designed to connect differently and I think the meter is used
in mA mode with them but not sure about that.

Is it a false expectation that the meter give me a 1/100 reading when used
with the probe in that manner? Is it also possible that the 1090M ohm is
giving me a "close enough" with that low voltage test and the difference
would become more measurable with higher voltages?

Sorry - this should be simple but, for some reason, I can't make it make
sense to me at the moment.

Thanks,
Barry - N4BUQ



Re: Must-Watch EEVBLOG video - Scoping Isolated and MainsEarth-Referenced equipment

Jason A.
 

Another good safety tip here from Mr. Carlson's Lab: https://www.youtube.com/watch?v=XBsQ3sZ45Fk&t=1s

Re: Tektronix 475 Oscilloscope - Help With Repair

John Arduino
 

Have you determined yet as to whether the heater in the CRT is glowing? [
you should be able to see it in a dark room].

//John KC1GJE

On Mon, Oct 28, 2019 at 9:22 AM <okkpik72@...> wrote:

I removed and tested the HV oscillator – Q1318 – and it tested fine.

I did find some cracked solder around the power transistor, which I
reflowed. No change.

I reflowed the solder around the other power transistors as well.

I reseated all the board connections. No change.



HV Probe and DMM Input Impedance

n4buq
 

This last weekend, I found an EICO HV probe in very nice condition at an estate sale. Opening it up, it contiains a 1.09G ohm resistor in series with the tip and cable. I connected it to the input of my Fluke 27 DMM and measured a low voltage source (all I had handy at that moment). From what I could tell, the probe gives me a 100x scale factor (e.g 10VDC measured 0.1VDC). While I may need to measure some higher voltages to confirm whether this is really accurate, it appears to be at least somewhat accurate.

I have a question, though, regarding the theory of the way this works. The Fluke has a 10M ohm input resistance which, if I'm thinking about this correctly, makes the measuring circuit 1100M ohms of which 10M ohm is the meter and the remaining resistance in the voltage divider network is the probe's resistor; however, I'm having trouble with the math.

Intuitively, (for me, at least), to obtain a 1/100 divider, I would think that ideally the probe resistance should be 0.990M ohms with the meter providing the remainin 10M ohms. But I find it odd that the resistor has that odd value which makes it seem like it was almost intended to work with a 10M device.

If I'm not mistaken, those probes were intended to be used with a particular device (meter) that provided the proper readings but not sure about that either (not finding a lot of info on this probe).

Am I off base here? I know that some of the HV probes designed to work with the Fluke are designed to connect differently and I think the meter is used in mA mode with them but not sure about that.

Is it a false expectation that the meter give me a 1/100 reading when used with the probe in that manner? Is it also possible that the 1090M ohm is giving me a "close enough" with that low voltage test and the difference would become more measurable with higher voltages?

Sorry - this should be simple but, for some reason, I can't make it make sense to me at the moment.

Thanks,
Barry - N4BUQ

Re: Tektronix 475 Oscilloscope - Help With Repair

necromancermi@...
 

I removed and tested the HV oscillator – Q1318 – and it tested fine.

I did find some cracked solder around the power transistor, which I reflowed. No change.

I reflowed the solder around the other power transistors as well.

I reseated all the board connections. No change.

Re: LCD screen for CSA803 or 1180x

Ed
 

Looks great, please supply more details.