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Re: Some advice needed on Tek curve tracers

"Raúl Martínez
 

Hi Dennis: Thanks for the tip, I will research past info on the group but you managed to give me the big picture, Size and Weight is for me a factor since I have to carry myself the unit during my next visit to the US, so I am inclined fro a 577.


Hi Jon: If you have a good 577 unit send me a private email to follow the issue, BTW Buenos Aires is located in Argentina, neighbor to Brazil. Payment should not be an issue and shipping should be to NY City.


Best Regards


Raul


Re: Some advice needed on Tek curve tracers

Bill (Doc) Courtright
 

Raul,
If the need is for just low level small signal transistor testing then I would suggest finding a 7CT1N or even a 5CT1N plug-in although those require either a 7000 or 5000 mainframe to use.
Otherwise there are non Tektronix options as Magnus said. I used the Heath IT-1121 myself before finding a 577.
Bill
KB3DKS

-----Original Message-----

Good Day, Raul,

I would like to second Dennis' advice here.

And expand it a little: The Tek 576 and 577 are great instruments, no
doubt. But they are also physically large and heavy instruments. Tek's
catalogue shows the 576 weight specification is 32 kilograms or 70.5 lbs!
Owning one would add yet another large device to my own "equipment
inventory". Also, these beauties are at least 3 decades old. And several
other group members had to repair their units...
So, I was considering that 99.9% of my needs in component testing are
for small transistors or diodes, a few years back. And I have found that
a small, portable curve tracer covers my own requirements a lot better.
And it only needs a minimum amount of real estate, as my labs/storage
space is limited.
Allow me a bit of self-promotion here: You shall find my write-up named
"Repairing a Heathkit IT-1121 curve tracer" in the archives. This gives
an example of a small, portable semiconductor curve tracer.

Cheers,

Magnus


Re: Introduction of myself!

Malcolm Hunter
 

On 15 February 2016 at 03:42, 'Dennis Tillman' @Dennis_Tillman_W7pF
[TekScopes] <TekScopes@...> wrote:

You need patience to snag bargains on Ebay.

​Ebay is really strange​. I've seen sellers continually listing and
relisting scopes with starting bid double what they usually sell for and
others practically giving them away. It's not like the expensive ones are
calibrated or anything.

Malcolm


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


Re: Some advice needed on Tek curve tracers

magnustoelle
 

Good Day, Raul,

I would like to second Dennis' advice here.

And expand it a little: The Tek 576 and 577 are great instruments, no doubt. But they are also physically large and heavy instruments. Tek's catalogue shows the 576 weight specification is 32 kilograms or 70.5 lbs!
Owning one would add yet another large device to my own "equipment inventory". Also, these beauties are at least 3 decades old. And several other group members had to repair their units...
So, I was considering that 99.9% of my needs in component testing are for small transistors or diodes, a few years back. And I have found that a small, portable curve tracer covers my own requirements a lot better. And it only needs a minimum amount of real estate, as my labs/storage space is limited.
Allow me a bit of self-promotion here: You shall find my write-up named "Repairing a Heathkit IT-1121 curve tracer" in the archives. This gives an example of a small, portable semiconductor curve tracer.

Cheers,

Magnus

On 14/02/2016 21:29, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] wrote:

Hi Raul,
The pro's and con's of both the 576 and the 577 (storage and non-storage)
have been discussed on this forum in great detail over the years. If you
take the time to go through the archives you can learn a great deal about
both instruments.

Personally the important thing to look for is one you can afford. Unless you
have some specific measurement requirement that only the 576 or the 577 can
do for you the differences between them are small compared to not owning a
curve tracer at all.

Dennis Tillman W7PF


Re: Some advice needed on Tek curve tracers

froggiegremlin
 

Hello all: Happy to offer my TEK 576 non-storage, for anyone interested.

I recall at least: Standard test fixture
SCR test fixture (turn off time, holding current) TEK 035-5028-00
Pulsed high current test fixture TEK 176
Many TO-3, TO-66, TO-220 and other adapters.

Items in USA, West coast.

If anyone interested, I can take pix and list what we have, and test it.

please contact me.


Kind Regards,

Jon


Re: 7904 - Very Dim Trace

Torch Fireman
 

I bought a length of 30kv wire last year for a reasonable price. It would be perfect for this application:

http://www.ebay.com/itm/222009647320?

use proper CAT rated leads if possible.


Re: 7904 - Very Dim Trace

Marian B
 

On 15.02.2016 06:13, jimmcintyre22@... [TekScopes] wrote:
I don't see that working. The idea was to measure 6.3 VAC that's
floating on -3kV DC.
If you have a few HV caps laying around, built a high-pass with them (a
corner frequency of a couple kHz is low enough), then you can measure
the AC with basically everything (RMS voltmeter, normal scope).

First power on, then connect probe ; depending on the dU/dt there might
be a hefty spike on turn on. Or shunt the output with some back-to-back
Zeners (>30 V).

Cheers, Marian


Re: 7904 - Very Dim Trace

Malcolm Hunter
 

I was thinking the same thing. Definitely don't want to keep clear of the
cheap meter when the DUT is turned on though and use proper CAT rated leads
if possible.

Malcolm

On 15 February 2016 at 12:16, Dwayne Verhey tekscopes@...
[TekScopes] <TekScopes@...> wrote:



How about floating a cheap Chinese meter instead? Ensure it is
electrically isolated from anything, including operator, connect the
leads with alligator clips, then turn on the power. If it doesn't blow
up it should be accurate enough for this measurement.

It's easier and less risky than attempting to float my TRMS Fluke at
-3 kV...
_

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


Re: 7904 - Very Dim Trace

Torch Fireman
 

How about floating a cheap Chinese meter instead? Ensure it is electrically isolated from anything, including operator, connect the leads with alligator clips, then turn on the power. If it doesn't blow up it should be accurate enough for this measurement.


It's easier and less risky than attempting to float my TRMS Fluke at
-3 kV...
_


Re: Tektronix 585

Anton Bgn
 

Hello Albert,

So, I try two new 6AU5, and the problem is still present...

Antoine


Re: PG502 power lamp off

Christoph
 

Thanks Brian, I didn't yet know of this database. It gives:






Transistor Part Number 151-0352-00 has the following equivalent generic types:

Generic Type Remarks D44C6 PWR, NPN, SI
Transistor type D44C6 has been assigned the following Tektronix part numbers:

Tek Part Number Remarks 151-0352-00 PWR, NPN, SI

Now that being a series regulator built around a µA723, I can find e.g. 2N3997 and 2N2580 in application examples in the data sheet. Both transistors don't seem suitable from the case construction point of view.

Taking the 1 Ohm current sense resistor one might calculate the required current. Didn't find a calculation example at the first glance.

VCE might be sufficient with 30V or so. The voltage drop is about 6.5 (since it is fed from 11.5V from the backplane).

A side question: looking at the circuit diagram around U640 (the µA 723) there is a remark at trim pot R645: "SET +15V"

Would that have to read "SET +5V"?


--
Christoph


Re: PG502 power lamp off

Christoph
 

Hi Dennis,

your objection may be justified. Only, in this case I had the strong suspicion that the 5V won't be there since the device doesn't show any sign of putting out any pulse. Right after posting my question here I was confirmed that I was right.

The +5V after the 1Ohm resistor were 0.7 V or so. I unsoldered the series regulator transistor Q650 also and measured open in every direction between b-c-e in either direction.


BTW, there was a mica isolation foil underneath the heat sink floating around and the hole for the fastening screw was empty.

Is there a screw normally in there? And is it isolated also from the backside if the PCB?
This is a plated through hole and I believe it carried GND, if I'm right. Since that kind of transistors normally have one electrode (c) connected to the heat sink I thinnk there should be a complete isolation kit in place.

--
Christoph


Re: 7904 - Very Dim Trace

 

On Mon, 15 Feb 2016 00:12:42 -0600, you wrote:

At 12 kilovolts, it was not as bright or sharp as when the 7904 is
using a 24 kilovolt PDA but it was close. Deflection was down about
10% versus being halved with no PDA at all.
Oh, and this means that it is possible that the high voltage
multiplier has been bad for some time and the calibration of your 7904
compensated for the slightly low deflection.


Re: 7904 - Very Dim Trace

 

One reason it will not work is that a standard high voltage multimeter
probe is not designed to operate much above 60 Hz and the heater
voltage is about 50 kHz.

A high voltage differential oscilloscope probe could do it.

On 14 Feb 2016 21:13:44 -0800, you wrote:

I don't see that working. The idea was to measure 6.3 VAC that's floating on -3kV DC.


Re: 7904 - Very Dim Trace

 

On 14 Feb 2016 20:04:24 -0800, you wrote:

No joy. The Service Manual Parts List calls out a 10 ohm series resistor in the heater, and that's what's in there. It measures 9.8 ohms. Re-checked deflection. Both X and Y are within 2%.
I'm still not convinced the 14kV is the only problem. This scope is new to me, and it could well have been 'mal-adjusted' to make up for the low PDA voltage. Still noodling on this. Continued comments welcomed...
I am not convinced either so I ran another test ...

I was considering how I could operate my 7904 with a 14 kilovolt PDA
to see how the CRT would behave but I lack a suitable power supply. I
do however have a 7603 sitting right next to the 7904 on the same desk
and it uses a 12 kilovolt PDA and the connectors are the same ...

So I reversed the 7603 to allow the anode lead to reach and connected
the PDA lead from the 7904 CRT to the 7603 power supply and powered
the 7904 up and then the 7603. It worked! I could even turn the 7603
off and watch the effect on the 7904 CRT as the PDA slowly discharged.

At 12 kilovolts, it was not as bright or sharp as when the 7904 is
using a 24 kilovolt PDA but it was close. Deflection was down about
10% versus being halved with no PDA at all.

So reducing the PDA to half of its nominal value had a minor but
noticeable effect on brightness and deflection. I think you have a
different problem causing a very dim CRT.

You have already verified that the output from the z-axis amplifier is
good and that the resistor in series with the heater is probably good
so I suspect the z-axis DC restorer. Did you make a measurement of
the actual grid to cathode voltage? This can also be done by floating
your Fluke...

The way the DC restorer works is that the difference between the
z-axis amplifier output and the grid bias voltage is subtracted from
the cathode voltage making the grid voltage more negative. Maybe
R1675 at the grid bias adjustment is open or the grid bias
potentiometer is bad.


Re: 7904 - Very Dim Trace

 

Nuke the Fluke, err, I mean float the Fluke.

It is the only way to be sure. :)

Carbon composition resistors have a high voltage coefficient of
resistance but that only applies at high voltages which this decidedly
is not.

If the thermal coefficient of resistance is a problem then the
resistor is bad and in that case, I would expect the nominal value to
be wrong as well.

On 14 Feb 2016 20:32:14 -0800, you wrote:

Sure - anything's possible I suppose. I now know that carbon comp resistors have a large voltage coefficient, but that's not really related to this. Anyway, changing out this resistor is pretty easy. I'll can give that a try...

It's easier and less risky than attempting to float my TRMS Fluke at -3 kV...


Re: 7904 - Very Dim Trace

Jim McIntyre
 

I don't see that working. The idea was to measure 6.3 VAC that's floating on -3kV DC.


Re: 7904 - Very Dim Trace

Brian Bloom
 

Apologies if my lack of experience + comments come as a possible irritation by some chance.

After all my time in construction and automotive, I have learned that it is better to state my ideas and thoughts regardless of their faults in the event they may trigger a new thought process in someone else and lead to the best outcome.

I wouldn't want to float a Fluke dmm at that voltage, either. What about making your own voltage divider x1000 probe for the application?


---In TekScopes@..., <jimmcintyre22@...> wrote :

Sure - anything's possible I suppose. I now know that carbon comp resistors have a large voltage coefficient, but that's not really related to this. Anyway, changing out this resistor is pretty easy. I'll can give that a try...

It's easier and less risky than attempting to float my TRMS Fluke at -3 kV...


Re: Introduction of myself!

 

On Sun, 14 Feb 2016 19:49:18 -0800, you wrote:

Hi David,
The delay is 75nSec as you said, but the risetime is 175pSec which is also a
consideration, although probably not for the 106 pulse generator which, I
suspect, has about a 1nSec risetime.
The service manual for the 106 recommends a Tektronix 4S3 which only
has a bandwidth of 1 GHz nicely matching the 7S14 or S1 so a 7M11
would be plenty fast.

I tried several ways to measure John Addis' little TD Pulse Generator
(067-0681-01) which had a 30pSec risetime and I could not use the 7M11. The
Random Sampling Mode of the 7T11 had so much time jitter on the fastest
sweep speeds that it didn't work either. In the end I had to give up.
I have had good results with random sampling mode on my 7T11A however
it is very finicky at best. Under ideal conditions, it easily met the
specified 30 picoseconds of jitter in random sampling mode.

The difficulty of knowing if the 7T11 is working correctly and
repairing it if not is why I would recommend a 7S14 instead despite
the battery issue.

Dennis Tillman W7PF


Re: Introduction of myself!

Brian Bloom
 

Certainly sounds like it would be easier to mod a 7s14 than deal with multiple units and their own independent costs and issues.

I managed to find Mercury cells of the correct voltage, though. Not to say that they are the correct physical size.. at $50 for 4 of them, I may as well just go thru with the mods so it'll just be done in the event those cells inevitably die. (hopefully I find a 7s14 in the near-er future!)


---In TekScopes@..., <davidwhess@...> wrote :

Each sampling input in the 7S14 takes 2 mercury cells so there are 4
cells total.

One option is to replace the original batteries with silver oxide or
alkaline cells. If the slightly higher voltage is a problem, then
either small signal schottky rectifiers can be added in series with
the batteries or the sampling drive circuit can be adjusted to produce
a slightly higher output by lowering the value of R15 and R17.

Another option is to use a photovoltaic optocoupler with a pair of
shunt diodes on the output to produce floating 1.35 volt supplies for
each sampling head.

I think doing the above would be easier than dealing with a
7S11/7T11/S1/S2.