Re: Probe bandwidth

Fabio Trevisan

Hi Bob,

I don't master all the theory on the passive probes, but when you put on
the same sentence the 50Ohm impedance and the probe capacitance; 20pF
(arguably.... More on this further down), it seems that you think the high
impedance passive probes such as the P6100 (10megohm at the tip, 1megohm at
the scope's input) work at the probe cable's characteristic impedance.
This can't be farther from the truth.
High impedance passive probes can't work at their cables characteristic
impedance because it that would be the case, to avoid all sort of
reflections and impedance mismatches, they would have to be terminated at
the scope's end with that characteristic impedance... And definitely
1megohm is not that, because I haven't seen a coax cable that can be made
with such high characteristic impedance.
High impedance passive probes are made with a special type of coax cable
where its resonant characteristic have been *critically damped* so not to
exhibit the *transmission line* characteristic of a regular coaxial cable.
This critical damping is achieved by making the inner conductor very thin,
wrinkled and resistive, at values in the 100s of ohms range.
The first patent (I think) of the concept were from Tek's John R. Kobbe,
and William Polits. It's patent US2883619A and the patent's text is a piece
of work.
Having said that, the thin wire aims at lowering the cable's cacapacitance,
increasing the frequency response, and furthermore proper selection of the
dielectric's properties of the insulating material allows for using the
least possible resistance for the inner wire, increasing the frequency
response.
Talking about the capacitance.. This value of 20pF you mention, I suppose
you're talking of the scope's input capacitance (to which the probe must be
able to compensate), because the chinese P6100 capacitance at the tip (in
x10 mode) is 13~17pF (and not 20), and in x1 mode it's 70~120pF (and of
course, the stated 100MHz applies only for x10 mode).
The capacitance at the tip is largely minimized by the 10:1 attenuation, as
the cable's capacitance is largely isolated from the tip (by the 9meg
resistor) and the tip basically only *sees* the compensation capacitor,
which only need to be about 1:10 of the sum of the cable's capacitance and
the scope's input capacitance.
The frequency response, in the end, is much more related to how good they
can make the cable (construction and dielectric wise) so to keep the
damping resistance of the inner wire to the minimum.
As the other folk mentioned, the Chinese P6100 gets there at 100MHz.
I can't tell they are as free of aberrations and ringing than the good
brands, but they get the basics covered.
Brgrds,
Fabio

On Jul 20, 2017 2:51 PM, "bob91343@... [TekScopes]" <
TekScopes@...> wrote:

I am confused regarding the stated bandwidth of an oscilloscope probe.

I thought that the bandwidth was computed from the input impedance, almost
purely capacitive at high frequencies. as the frequency where the reactance
drops to 50 Ohms.

This idea seems to work most of the time but I am seeing some probes with
stated bandwidth somewhat higher. For instance I see some Chinese probes
advertised as 100 MHz, 200 MHz, even higher, yet their input capacitance is
still around 20 pF more or less.

Before you jump down my throat about how terrible Chinese stuff is, let's
keep it at a technical level and explain just what bandwidth means so I can

I see probes very cheap (not really rugged but still a good value) for
various prices from around \$4 to \$13 but they appear to be the same, except
for the bandwidth rating. How can this be?

Since my use is very casual and I don't need to pay for high quality, this
is a somewhat important question. And of course, after a few years they
fall apart and I need to purchase again, but over my lifetime I don't
usually get to where I have spent the same money as for a Tek or HP probe.

Bob

[Non-text portions of this message have been removed]

d

[Non-text portions of this message have been removed]

Re: Probe bandwidth

bc

My take on the cheap probes:
I bought a pair of those cheap "Jinhao" P6100 x1/x10 "100MHz" chinese
probes, as my 20MHz scope would use them fine if they turn out to be
junk.  I also have some real Tektronix P6120's.  For the heck of it I
built an avalanche pulser on a solderless breadboard (yeah, yeah, cap
cap cap...) to try to measure rise time.  I measured on my 2465.
With some margin of error, I got about 2ns risetime with the P6100s and
1.9ns with the P6120.
Seems both are fast enough for their rating.  I suspect because of the
just under 2ns risetime, some sellers will fudge it to 200MHz despite
it's not quite there, or perhaps just so happen to have a bit less
capacitance and will do 200MHz.
I do have to warn about the P6100's : They will not take abuse.  Expect
the wires to break off of their connectors (the alligator clip and the
BNC specifically).  The hook clip head that came with them are really
"fat" though sturdy, I would have reservation using them on even 0.1"
DIPs for worries of shorts.  (I've had some hook clips that are small
enough that I would have no reservation hot clipping onto live
circuits, but the P6100 I'd not even try.)
I am overall satisfied with the P6100s, but I'm doing a disservice to
my 2440 and 2465, they deserve higher bandwidth probes :-(
Note: This is just one sample.  I don't know if all of these probes
have the same characteristics so YMMV.

On Thu, 2017-07-20 at 17:51 +0000, bob91343@... [TekScopes]
wrote:

I am confused regarding the stated bandwidth of an oscilloscope
probe.

I thought that the bandwidth was computed from the input impedance,
almost purely capacitive at high frequencies. as the frequency where
the reactance drops to 50 Ohms.

This idea seems to work most of the time but I am seeing some probes
with stated bandwidth somewhat higher.  For instance I see some
Chinese probes advertised as 100 MHz, 200 MHz, even higher, yet their
input capacitance is still around 20 pF more or less.

Before you jump down my throat about how terrible Chinese stuff is,
let's keep it at a technical level and explain just what bandwidth
means so I can decide what to buy.

I see probes very cheap (not really rugged but still a good value)
for various prices from around \$4 to \$13 but they appear to be the
same, except for the bandwidth rating.  How can this be?

Since my use is very casual and I don't need to pay for high quality,
this is a somewhat important question.  And of course, after a few
years they fall apart and I need to purchase again, but over my
lifetime I don't usually get to where I have spent the same money as
for a Tek or HP probe.

Bob

[Non-text portions of this message have been removed]

<!--
#ygrp-mkp {
border: 1px solid #d8d8d8;
font-family: Arial;
margin: 10px 0;
}

#ygrp-mkp hr {
border: 1px solid #d8d8d8;
}

#ygrp-mkp #hd {
color: #628c2a;
font-size: 85%;
font-weight: 700;
line-height: 122%;
margin: 10px 0;
}

margin-bottom: 10px;
}

}

margin: 0;
}

color: #0000ff;
text-decoration: none;
}
font-family: Arial;
}

margin: 10px 0px;
font-weight: 700;
font-size: 78%;
line-height: 122%;
}

margin-bottom: 10px;
}

#actions {
font-family: Verdana;
font-size: 11px;
}

#activity {
background-color: #e0ecee;
float: left;
font-family: Verdana;
font-size: 10px;
}

#activity span {
font-weight: 700;
}

#activity span:first-child {
text-transform: uppercase;
}

#activity span a {
color: #5085b6;
text-decoration: none;
}

#activity span span {
color: #ff7900;
}

#activity span .underline {
text-decoration: underline;
}

.attach {
clear: both;
display: table;
font-family: Arial;
font-size: 12px;
width: 400px;
}

.attach div a {
text-decoration: none;
}

.attach img {
border: none;
}

.attach label {
display: block;
margin-bottom: 5px;
}

.attach label a {
text-decoration: none;
}

blockquote {
margin: 0 0 0 4px;
}

.bold {
font-family: Arial;
font-size: 13px;
font-weight: 700;
}

.bold a {
text-decoration: none;
}

dd.last p a {
font-family: Verdana;
font-weight: 700;
}

dd.last p span {
margin-right: 10px;
font-family: Verdana;
font-weight: 700;
}

dd.last p span.yshortcuts {
margin-right: 0;
}

div.attach-table div div a {
text-decoration: none;
}

div.attach-table {
width: 400px;
}

div.file-title a, div.file-title a:active, div.file-title a:hover,
div.file-title a:visited {
text-decoration: none;
}

div.photo-title a, div.photo-title a:active, div.photo-title
a:hover, div.photo-title a:visited {
text-decoration: none;
}

div#ygrp-mlmsg #ygrp-msg p a span.yshortcuts {
font-family: Verdana;
font-size: 10px;
font-weight: normal;
}

.green {
color: #628c2a;
}

.MsoNormal {
margin: 0 0 0 0;
}

o {
font-size: 0;
}

#photos div {
float: left;
width: 72px;
}

#photos div div {
border: 1px solid #666666;
height: 62px;
overflow: hidden;
width: 62px;
}

#photos div label {
color: #666666;
font-size: 10px;
overflow: hidden;
text-align: center;
white-space: nowrap;
width: 64px;
}

#reco-category {
font-size: 77%;
}

#reco-desc {
font-size: 77%;
}

.replbq {
margin: 4px;
}

#ygrp-actbar div a:first-child {
/* border-right: 0px solid #000;*/
margin-right: 2px;
}

#ygrp-mlmsg {
font-size: 13px;
font-family: Arial, helvetica,clean, sans-serif;
*font-size: small;
*font: x-small;
}

#ygrp-mlmsg table {
font-size: inherit;
font: 100%;
}

#ygrp-mlmsg select, input, textarea {
font: 99% Arial, Helvetica, clean, sans-serif;
}

#ygrp-mlmsg pre, code {
font:115% monospace;
*font-size:100%;
}

#ygrp-mlmsg * {
line-height: 1.22em;
}

#ygrp-mlmsg #logo {
}

#ygrp-msg p a {
font-family: Verdana;
}

#ygrp-msg p#attach-count span {
color: #1E66AE;
font-weight: 700;
}

color: #ff7900;
font-weight: 700;
}

#ygrp-reco {
margin-bottom: 20px;
}

font-size: 130%;
text-decoration: none;
}

font-size: 77%;
list-style-type: square;
}

margin: 0;
}

#ygrp-text {
font-family: Georgia;
}

#ygrp-text p {
margin: 0 0 1em 0;
}

#ygrp-text tt {
font-size: 120%;
}

#ygrp-vital ul li:last-child {
border-right: none !important;
}
-->

Re: "Lamps" wiring on 7000-series mainframes.

Colin Herbert

Hi,

I wonder if anyone can see a reason why this circuit won't work to give a
minimum of 0V and a maximum of +5V for the plug-in lights.

The idea is that with R2 at maximum, R3 is adjusted to give a maximum +5V
out. Then R2 can be a screwdriver access control to reduce the voltage to
the lights. The 500R pre-set is used because +5V requires 360R and R2 is
chosen as 10k simply because that is what I had available. Any comments?

Colin.

From: TekScopes@... [mailto:TekScopes@...]
Sent: 14 October 2015 16:57
Cc: TekScopes
Subject: Re: [TekScopes] "Lamps" wiring on 7000-series mainframes.

Unless you like changing lamps, I suggest using a lower voltage than 5V...
at least put a diode or 2 in series.

TekScopes@...

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the TekScopes
group.

File : /+5V regulated001.pdf
Description : Circuit for adjustable o to +5V regulated supply for 7000-series lights

You can access this file at the URL:
https://groups.yahoo.com/neo/groups/TekScopes/files/%2B5V%20regulated001.pdf

https://help.yahoo.com/kb/index?page=content&y=PROD_GRPS&locale=en_US&id=SLN15398

Regards,

pervy_tango <colingherbert@...>

Probe bandwidth

Bob Albert

I am confused regarding the stated bandwidth of an oscilloscope probe.

I thought that the bandwidth was computed from the input impedance, almost purely capacitive at high frequencies. as the frequency where the reactance drops to 50 Ohms.

This idea seems to work most of the time but I am seeing some probes with stated bandwidth somewhat higher. For instance I see some Chinese probes advertised as 100 MHz, 200 MHz, even higher, yet their input capacitance is still around 20 pF more or less.

Before you jump down my throat about how terrible Chinese stuff is, let's keep it at a technical level and explain just what bandwidth means so I can decide what to buy.

I see probes very cheap (not really rugged but still a good value) for various prices from around \$4 to \$13 but they appear to be the same, except for the bandwidth rating. How can this be?

Since my use is very casual and I don't need to pay for high quality, this is a somewhat important question. And of course, after a few years they fall apart and I need to purchase again, but over my lifetime I don't usually get to where I have spent the same money as for a Tek or HP probe.

Bob

Re: Just lost horizontal deflection on my 2465

rovmkr

Does anyone have any experience with the Thomas Lafay adapter?
Has anyone attempted to get this adapter working?
Peter.

Tom Jobe <tomjobe@...>

Another thing to add to the Kelvin discussion, is that the Tektronix
Kelvin connections that go to the curve tracer.
They have either 5 or 6 connections on the back and connect to the both
the left and right CBE socket rows. The 5 connection model is missing
the E pin for the right side connections.
After thinking about which test fixture I find most useful, it would
probably be the diode fixture.
For example, you want to go through some zeners and find the one with
the 'knee' that is closest to some value or has the 'squarest' knee. It
makes that kind of job quick and easy.
The older style diode fixture 013-0111-00 has Kelvin connections. The
newer style 013-072 does not have Kelvin connections but it's my
favorite of the two.
There are usually some of the "Stud Diode" fixtures 013-0110-00 for sale
on eBay and elsewhere, and I find that they are fairly useless except to
steal parts out of.
tom jobe...

On 7/20/2017 5:44 AM, Chuck Harris cfharris@... [TekScopes] wrote:

It is not exactly difficult to make alligator clips with
two leads and banana plugs for those cases... however, in
the current ranges the plain old 576 is capable of generating,
you will notice very little difference between a 2 inch
I rather doubt you will notice any.

I have a fair number of tektronix adapters, but don't use
them much, using the alligator clip method most of the time.

If you use small, insulated alligator clips, you won't have
to bend up the DUT's leads to make it fit the tektronix adapter.

And, many of the tektronix adapters are only usable with full

another that uses tiny 3/4 inch long alligators.

-Chuck Harris

'Craig Sawyers' c.sawyers@... [TekScopes] wrote:
I'm not sure why you would want to short collector to base for any
bipolar transistor measurement.
But shorting drain to source is needed for measuring gate-source
breakdown voltage V(BR)GSS and
reverse gate leakage IGSS. The bottom one re-wires the emitter or
gate connection, to swap from ebc
to ecb transistor (or equivalent fet) leadouts.

The benefit of using the correct fixtures for the 576 is that they
make true kelvin connections to
the DUT, and so improve measurement accuracy if significant currents
flow.

Craig

------------------------------------
Posted by: "Craig Sawyers" <c.sawyers@...>
------------------------------------

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

[Non-text portions of this message have been removed]

Craig Sawyers <c.sawyers@...>

It is not exactly difficult to make alligator clips with two leads and banana plugs for those
cases...
however, in the current ranges the plain old 576 is capable of generating, you will notice very
little
difference between a 2 inch lead made of #22 gage stranded wire, and the Kelvin clip...
I rather doubt you will notice any.
There are many Kelvin clips from Chinese suppliers at exceptionally low prices. I've bought two entire
lead sets from this source (one with BNC's and one with banana plugs) equipped with Kelvin clips for a
fraction of the price you pay for a western supplied kelvin clip.

Craig

Chuck Harris

It is not exactly difficult to make alligator clips with
two leads and banana plugs for those cases... however, in
the current ranges the plain old 576 is capable of generating,
you will notice very little difference between a 2 inch
I rather doubt you will notice any.

I have a fair number of tektronix adapters, but don't use
them much, using the alligator clip method most of the time.

If you use small, insulated alligator clips, you won't have
to bend up the DUT's leads to make it fit the tektronix adapter.

And, many of the tektronix adapters are only usable with full

another that uses tiny 3/4 inch long alligators.

-Chuck Harris

'Craig Sawyers' c.sawyers@... [TekScopes] wrote:

I'm not sure why you would want to short collector to base for any bipolar transistor measurement.
But shorting drain to source is needed for measuring gate-source breakdown voltage V(BR)GSS and
reverse gate leakage IGSS. The bottom one re-wires the emitter or gate connection, to swap from ebc
to ecb transistor (or equivalent fet) leadouts.

The benefit of using the correct fixtures for the 576 is that they make true kelvin connections to
the DUT, and so improve measurement accuracy if significant currents flow.

Craig

------------------------------------
Posted by: "Craig Sawyers" <c.sawyers@...>
------------------------------------

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

Brent Watson <brentleew2003@...>

Good info, thanks Craig

On Wednesday, July 19, 2017, 11:38:59 PM PDT, 'Craig Sawyers' c.sawyers@... [TekScopes] <TekScopes@...> wrote:

I'm not sure why you would want to short collector to base for any bipolar transistor measurement.
But shorting drain to source is needed for measuring gate-source breakdown voltage V(BR)GSS and
reverse gate leakage IGSS. The bottom one re-wires the emitter or gate connection, to swap from ebc
to ecb transistor (or equivalent fet) leadouts.

The benefit of using the correct fixtures for the 576 is that they make true kelvin connections to
the DUT, and so improve measurement accuracy if significant currents flow.

Craig

[Non-text portions of this message have been removed]

OT: Anyone in UK (or Europe) likely to be placing an order with Lemo in the near future

If so I'd very much like to piggy back on your order to avoid the GBP100
plus VAT MOV.

Thanks
David

OT: Manuals for Datron (Wavetek) 4808 Option 70 Wideband Source

Hi everyone,

I have the Schematics and Parts list for this on loan at present, but I have
had no luck finding any other documentation for it.

The edition of the user handbook for the 4808 that I have is too early to

I'm looking for a more up to date version of the 4808 User Manual, and the
User and Service documentation for Option 70

Hoping that someone can help with either real "dead tree" manuals or with
scans.

Thanks
Dave

Craig Sawyers <c.sawyers@...>

I'm not sure why you would want to short collector to base for any bipolar transistor measurement.
But shorting drain to source is needed for measuring gate-source breakdown voltage V(BR)GSS and
reverse gate leakage IGSS. The bottom one re-wires the emitter or gate connection, to swap from ebc
to ecb transistor (or equivalent fet) leadouts.

The benefit of using the correct fixtures for the 576 is that they make true kelvin connections to
the DUT, and so improve measurement accuracy if significant currents flow.

Craig

Tektronix 454

erik erickson

Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone

Brent Watson <brentleew2003@...>

Thanks Brad,Well done.  I'll print that and put in my "Projects To Do" file
I look forward to projects like that.Brent

On Wednesday, July 19, 2017, 6:09:42 PM PDT, Brad Thompson brad.thompson@... [TekScopes] <TekScopes@...> wrote:

On 7/19/2017 8:15 PM, Tom Jobe tomjobe@... [TekScopes] wrote:
Hi Brent,
I see that you did not get an answer about the 'push buttons' on the
sides of curve tracer adapters such as the 013-0098-0x.
Hello--

Dunno whether this might prove helpful or merely thought-provoking, but
here's a fixture I used with a Tek 575 for vacuum-tube evaluation (within
the 575's test-voltage limits):

...Scroll to the bottom of...

https://www.flickr.com/photos/aa1ip_pix/

...For a schematic. I designed a patch panel that plugs into the 575's DUT
(device under test) binding posts via flying leads. I used ExpressPCB's
miniboard
service to fabricate the patch panel.

Using some surplus two-piece wiring blocks, I configured a jumper kludge
that
routed signals to and from the tube socket. External sources supply heater
and screen voltages-- investigate your collection of "wall warts" for likely
heater-voltage sources. Always verify that the source is delivering
something
close to the tube's specified heater voltage.

For screen voltage, you can use a variable-output current-limited bench
supply
capable of delivering 50- 150 volts, or a power-over-ethernet (POE)
supply that
delivers 48 VDC. Use an external potentiometer to set the needed screen
voltage.

Limitations: this approach works best when you need to evaluate and
match a group
of tubes of the same type. The 575's relatively low upper
collector-voltage limit (200 V)
restricts applications to receiving tubes.

Parasitic oscillations due to the relatively long leads connecting the
tube's elements
may manifest as fuzzy areas on displayed traces. If necessary, adding
or low-value (10-100 Ohm) carbon-composition resistors in series with
the grid
and plate leads at the tube socket will help suppress the parasitics.

Finally, note that most receiving tubes' published specifications state
a maximum control-grid voltage of zero volts POSITIVE. Make sure that
the curve-tracer's base-voltage step polarity is always negative-going
with zero
positive-voltage offset. Accidentally running the control-grid positive
with plate current set at a high level leads to an impressive fireworks
display as
the grid overheats<g>.

73--

[Non-text portions of this message have been removed]

Brent Watson <brentleew2003@...>

Thanks Tom, that was very helpful, and thank you also Chuck.
Now I see the purpose of the push-buttons. I guess they could help. I see what you mean about their value testing in quantity.
I don't have anything yet. Just using banana jacks, leads and alligator clips on my 7ct1n.
I thought there might be some literature on them somewhere but a little trial and error will work too.

My 576 is still in Santa Ana, Ca.  Where I purchased it, and I'm in the SF bay area.  My travel plans to San Diego changed so I have to figure how to get the 576 up here. Maybe there's a Tek fan coming this way. I would be happy to contribute fuel costs and a steak dinner if you were.

brentleew2003@...

Brent

On Wednesday, July 19, 2017, 5:15:43 PM PDT, Tom Jobe tomjobe@... [TekScopes] <TekScopes@...> wrote:

Hi Brent,
I see that you did not get an answer about the 'push buttons' on the
sides of curve tracer adapters such as the 013-0098-0x.
I don't know much about the push buttons and their purpose, but here are
a few thoughts about it all.
The push buttons are spring loaded so you can put a wire in the adjacent
hole (on the top side of the fixture) to get a fairly direct connection
to the C,B or E sockets on the curve tracer.
These adapters often come with a bent "U" shaped jumper wire that will
short any two adjacent holes (C to B on either side, or E to E across
the bottom).
This original bent wire jumper is made of 1/16"/1.5mm wire.
There is a little bit of additional confusion that depends on which dash
bottom wire holes and the later -01 and -02 adapters are marked E on the
left side hole and a have a yellow dot on the right side wire hole. In
addition the -00 and -01 adapters have six pins that plug into your
curve tracer, whereas the -02 only has five pins.
All of the E test part sockets on the adapter seem to be connected
together and to the left socket on the curve tracer on the -01 and -02,
but on the -00 the E part test sockets seem to not be connected together
in the test fixture, but have the sixth pin for separate connections to
the curve tracer's sockets.
I don't understand all of this as the 576 curve tracer has both E
sockets connected together internally using the normal settings for
something like a transistor or diode.
The FET version of this same adapter (013-0099-0x has the test sockets
marked DGS instead of CBE, but it's probably wired about the same
internally.
I don't find this style of test adapter that be all that useful, and you
might consider Chuck Harris' excellent idea of some banana plugs,
alligator clips and short wires for general use at very low cost.
I have lots of test adapters for my Tektronix curve tracers, but they
seem to be more of a convenience for doing lots of testing which
hobbyists like us might not do that much of.
tom jobe...

On 7/18/2017 11:51 AM, brentleew2003@... [TekScopes] wrote:

I want to purchase an adapter for my 576 I recently purchased, but I'm
not sure what the difference between the Transistor, FET or
combination version is. A couple of questions- 1. Are the 013-0098-00,
013-0098-01 and 013-0098-02, wired differently, or is it just
labeling. 2. Is the bar at top front for emitter/source grounding or
separating the two sides, and finally what are the pushbuttons on the
sides for. I have not seen documentation for these as yet. Thanks and
Cheers,
Brent

[Non-text portions of this message have been removed]

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

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

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

[Non-text portions of this message have been removed]

On 7/19/2017 8:15 PM, Tom Jobe tomjobe@... [TekScopes] wrote:
Hi Brent,
I see that you did not get an answer about the 'push buttons' on the
sides of curve tracer adapters such as the 013-0098-0x.
Hello--

Dunno whether this might prove helpful or merely thought-provoking, but
here's a fixture I used with a Tek 575 for vacuum-tube evaluation (within
the 575's test-voltage limits):

...Scroll to the bottom of...

https://www.flickr.com/photos/aa1ip_pix/

...For a schematic. I designed a patch panel that plugs into the 575's DUT
(device under test) binding posts via flying leads. I used ExpressPCB's miniboard
service to fabricate the patch panel.

Using some surplus two-piece wiring blocks, I configured a jumper kludge that
routed signals to and from the tube socket. External sources supply heater
and screen voltages-- investigate your collection of "wall warts" for likely
heater-voltage sources. Always verify that the source is delivering something
close to the tube's specified heater voltage.

For screen voltage, you can use a variable-output current-limited bench supply
capable of delivering 50- 150 volts, or a power-over-ethernet (POE) supply that
delivers 48 VDC. Use an external potentiometer to set the needed screen voltage.

Limitations: this approach works best when you need to evaluate and match a group
of tubes of the same type. The 575's relatively low upper collector-voltage limit (200 V)
restricts applications to receiving tubes.

Parasitic oscillations due to the relatively long leads connecting the tube's elements
may manifest as fuzzy areas on displayed traces. If necessary, adding ferrite beads
or low-value (10-100 Ohm) carbon-composition resistors in series with the grid
and plate leads at the tube socket will help suppress the parasitics.

Finally, note that most receiving tubes' published specifications state
a maximum control-grid voltage of zero volts POSITIVE. Make sure that
the curve-tracer's base-voltage step polarity is always negative-going with zero
positive-voltage offset. Accidentally running the control-grid positive
with plate current set at a high level leads to an impressive fireworks display as
the grid overheats<g>.

73--

Re: Scope face focus anomaly

I was a Field Eng for Tek when the 465 was announced.A common complaint from customers was poor focus, esp when compared to the 453, which was its predecessor.This overlooks the fact that the 465 had a much bigger display.

The focus is impacted by an expansion mesh inside the CRT, which was there to improve the geometry.
This is a dome-shaped mesh which the electron beam must pass thru on its way to the phosphor.When the beam goes through it, it fans out a little, much like squirting a garden hose through a window screen.
Do you want a display which is big, or do you want it sharp & crisp ?
HankC, Boston WA1HOS

[Non-text portions of this message have been removed]

Tom Jobe <tomjobe@...>

Hi Brent,
I see that you did not get an answer about the 'push buttons' on the
sides of curve tracer adapters such as the 013-0098-0x.
I don't know much about the push buttons and their purpose, but here are
a few thoughts about it all.
The push buttons are spring loaded so you can put a wire in the adjacent
hole (on the top side of the fixture) to get a fairly direct connection
to the C,B or E sockets on the curve tracer.
These adapters often come with a bent "U" shaped jumper wire that will
short any two adjacent holes (C to B on either side, or E to E across
the bottom).
This original bent wire jumper is made of 1/16"/1.5mm wire.
There is a little bit of additional confusion that depends on which dash
bottom wire holes and the later -01 and -02 adapters are marked E on the
left side hole and a have a yellow dot on the right side wire hole. In
addition the -00 and -01 adapters have six pins that plug into your
curve tracer, whereas the -02 only has five pins.
All of the E test part sockets on the adapter seem to be connected
together and to the left socket on the curve tracer on the -01 and -02,
but on the -00 the E part test sockets seem to not be connected together
in the test fixture, but have the sixth pin for separate connections to
the curve tracer's sockets.
I don't understand all of this as the 576 curve tracer has both E
sockets connected together internally using the normal settings for
something like a transistor or diode.
The FET version of this same adapter (013-0099-0x has the test sockets
marked DGS instead of CBE, but it's probably wired about the same
internally.
I don't find this style of test adapter that be all that useful, and you
might consider Chuck Harris' excellent idea of some banana plugs,
alligator clips and short wires for general use at very low cost.
I have lots of test adapters for my Tektronix curve tracers, but they
seem to be more of a convenience for doing lots of testing which
hobbyists like us might not do that much of.
tom jobe...

On 7/18/2017 11:51 AM, brentleew2003@... [TekScopes] wrote:

I want to purchase an adapter for my 576 I recently purchased, but I'm
not sure what the difference between the Transistor, FET or
combination version is. A couple of questions- 1. Are the 013-0098-00,
013-0098-01 and 013-0098-02, wired differently, or is it just
labeling. 2. Is the bar at top front for emitter/source grounding or
separating the two sides, and finally what are the pushbuttons on the
sides for. I have not seen documentation for these as yet. Thanks and
Cheers,
Brent

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Re: CRT Tube (in good shape) for Tek464 / Tek466