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7904 or 7904A....which should I keep?

Chris Wilkson
 

Title says it all. I have multiple (MULTIPLE!) Tek mainframes and I'm hoping to cull the herd this year. I want to keep one 500MHz scope and it's either the 7904 or 7904A.

What are the advantages and disadvantages of each? Do they both support the full range of plugins (looking at power hungry digital stuff) or is one more forgiving. What about fan noise, availability of parts, ease of repair & cal & maintenance? Control panel features? Current loop vs. voltage calibration outputs? Display quality?

All opinions are welcome!!


Re: 5116+5D10 intensity problem

Harvey White
 

You're welcome.  I don't know if you have the particular HV transformer, but as Chuck (next) says, you're definitely looking at a low high voltage, so the question, of course, is why....

For the probe:  That's likely a P6015 or the equivalent.  It may be used with or without the dielectric liquid.  WIth, I think that the rating is 30KV, without, about 18KV.  You should be fine without it.   You may want to try using it with an adaptor with a meter, but it is designed to work into a 1 meg input impedance, and most meters are 10.  Paralleling the meter input to make it 1 meg is recommended if you try this.  I'd also try a test run (if you do that) on a known 100 volt or so supply to make sure you get the required 0.1 volt on the meter.  If not, then you're using it on a scope, and while you'll get a good idea, of voltage, it will only be within about 5% or so unless you have an A/D plugin.  The 5D10 might just do for that if you could see the readouts.

I recommend hunting the internet for the manuals for everything you have, if you haven't already.  I have an electronic library in several places.  Some of that information is available for only a limited time.

Harvey

On 2/17/2020 3:22 AM, Yeun-Jung Wu wrote:
Hello Harvey:

Thank you for your hint on future diagnosis. I will start collecting more information on epoxy coated transformer first.

5D10 seemed to work fine except read out information had been expanded outside the screen. Now I understand why red LED "possible under-sampling" would lit: I was using slow time base to watch two nearly identical 7kHz since wave superimposed together to form a nice envelope. There were lot of wave form variation during long accuqsition time but the available memory space for storing waveform was limited. When I select faster time base such that several cycles was within the range of one horizontal division that warning went away.

More than 5 year's ago I bought a Tek high voltage probe from eBay. There was an empty can supposed to contain liquid with high dielectric strength, something similar to banned CFC freon. For 4.5kV maybe I can fill some other liquid and give it a try.

Best Regards,

Yeun-Jung Wu



Re: help tek 475 power supply

Chuck Harris
 

Because you don't get a lot of room to route the heavy
traces needed in a power supply, with a two layer circuit
board, designers very often used cheats, like using the
fact that all of the negative lugs on twist lock electrolytic
capacitors are connected together, to make no cost
jumper wires used to make circuit board routing easier.

If you didn't make sure that all of the twist lugs on the
capacitors you replaced have wire jumpers to make those
connections, your supply will be very confused.

-Chuck Harris

Roberto wrote:

hello everyone after changing the electrolytic capacitors on my teak 475 I have a problem that turned on after a few minutes it turns off I checked that the transistor Q1446 2n2222 was defective due to the fact that it looks like a 24v zener diode with a 180 series resistor hom that heats up and makes you break some ideas?
Roberto




Re: 5116+5D10 intensity problem

Chuck Harris
 

When the Anode voltage on the CRT is lower than it is supposed to
be, the electrons in the beam travel proportionately slower than
they should. Because they are slower, they spend a longer amount
of time to passing between the deflection plates. This means
longer time means that the force the electric field between the
plates applies to the electrons, has a longer time to work at
deflecting the electron beam. Which further means the electron
beam will be deflected more than it would at the proper voltage.

What you should take away from this is: If the anode voltage is
low, everything on the CRT screen will be expanded (magnified) out
much larger than it should be.

That your readout is expanded outside of the screen is nearly
perfect proof that your anode voltage is low. You can guestimate
how low by how much the expansion is. But it is most definitely
lower than it should be.

-Chuck Harris

Yeun-Jung Wu wrote:

Hello Harvey:

Thank you for your hint on future diagnosis. I will start collecting more information on epoxy coated transformer first.

5D10 seemed to work fine except read out information had been expanded outside the screen. Now I understand why red LED "possible under-sampling" would lit: I was using slow time base to watch two nearly identical 7kHz since wave superimposed together to form a nice envelope. There were lot of wave form variation during long accuqsition time but the available memory space for storing waveform was limited. When I select faster time base such that several cycles was within the range of one horizontal division that warning went away.

More than 5 year's ago I bought a Tek high voltage probe from eBay. There was an empty can supposed to contain liquid with high dielectric strength, something similar to banned CFC freon. For 4.5kV maybe I can fill some other liquid and give it a try.

Best Regards,

Yeun-Jung Wu


help tek 475 power supply

Roberto
 

hello everyone after changing the electrolytic capacitors on my teak 475 I have a problem that turned on after a few minutes it turns off I checked that the transistor Q1446 2n2222 was defective due to the fact that it looks like a 24v zener diode with a 180 series resistor hom that heats up and makes you break some ideas?
Roberto


Re: 5116+5D10 intensity problem

Yeun-Jung Wu
 

Hello Harvey:

Thank you for your hint on future diagnosis. I will start collecting more information on epoxy coated transformer first.

5D10 seemed to work fine except read out information had been expanded outside the screen. Now I understand why red LED "possible under-sampling" would lit: I was using slow time base to watch two nearly identical 7kHz since wave superimposed together to form a nice envelope. There were lot of wave form variation during long accuqsition time but the available memory space for storing waveform was limited. When I select faster time base such that several cycles was within the range of one horizontal division that warning went away.

More than 5 year's ago I bought a Tek high voltage probe from eBay. There was an empty can supposed to contain liquid with high dielectric strength, something similar to banned CFC freon. For 4.5kV maybe I can fill some other liquid and give it a try.

Best Regards,

Yeun-Jung Wu


Scope auction

Robert Simpson
 

About the middle of the page:
https://www.estatesales.net/CA/Rocklin/95677/2475516

No connection, but is in a neighboring town.
That 7904A looks like it has 7S12 in it with modules
Bob


Re: The Everlasting 547 HV Transformer topic

Chuck Harris
 

Hi Leonard,

I replied to you minutes after your first request, and the same
after your second request. But your spam filter obviously doesn't
like me. I suggest you check your spam folder.

Here is what I replied:
----------------------------------------
Hi Leonard,

I sent you the below message at 12:53 on Feb 5th.
-------------------------------------------------------------------------
Hi Leonard,

I am working feverishly on finishing my new winding machine.
It is computer controlled, and will make winding HV transformers
much easier, and more reliable.

I have been promising that I would be ready really soon now, for
about the last 5 years... I don't like making promises that I can't
keep.... so I won't do that anymore.

However, I am now retired, so in theory, I have more time on my
hands.

I will post an announcement on the tekscopes, and tekscopes2 groups
when I am ready to start winding again.

-Chuck Harris
----------------------------------------

leonard scheepsma wrote:

Guys,
I've once again restored a 547 almost at the edge of the dirt container, got it working (except then both time-bases A & B do not trigger but that's for later as I run an 1S2 right now which doesn't need it anyway) but the scope shows all symptoms of a defective HV transformer (20 mins show time and then dies on me..)

So, I read Chuck Harris is the man who could possibly make me a replacement. For a 549 I have as well, I got an Xfrm winded locally, but that was no success (spraying), for that scope a small blower entered the HV case which solved the problem as the temperature doesn't rise so much. For this 547 I'm very interested to have a real good replacement.

I've sent a direct email to Chuck a few times but got no response yet. He is around right?

Thanks Leonard




Re: 475 Module: Anyone need it?

Renée
 

Hi Bruce-
I use the 475  as my preferred scope...so If it is still available...I will take it.
we should do this off list from here ....k6fsb dot 1 at the gmail place
Renée

On 2/16/20 10:43 AM, Bruce Lane wrote:
Fellow Tekkies,

While hunting for a part this morning, I came across a Tektronix module
which I think is the vertical driver board for a 460 or 470 series. The
part number is 670-3023-02.

I don't need it, as I sold my 475 some time ago. First offer of $5 plus
postage gets it, priority to those who might need the thing to repair an
existing 'scope.

Thanks much.


475 Module: Anyone need it?

Bruce Lane
 

Fellow Tekkies,

While hunting for a part this morning, I came across a Tektronix module
which I think is the vertical driver board for a 460 or 470 series. The
part number is 670-3023-02.

I don't need it, as I sold my 475 some time ago. First offer of $5 plus
postage gets it, priority to those who might need the thing to repair an
existing 'scope.

Thanks much.

--
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)


The Everlasting 547 HV Transformer topic

leonard scheepsma
 

Guys,
I've once again restored a 547 almost at the edge of the dirt container, got it working (except then both time-bases A & B do not trigger but that's for later as I run an 1S2 right now which doesn't need it anyway) but the scope shows all symptoms of a defective HV transformer (20 mins show time and then dies on me..)

So, I read Chuck Harris is the man who could possibly make me a replacement. For a 549 I have as well, I got an Xfrm winded locally, but that was no success (spraying), for that scope a small blower entered the HV case which solved the problem as the temperature doesn't rise so much. For this 547 I'm very interested to have a real good replacement.

I've sent a direct email to Chuck a few times but got no response yet. He is around right?

Thanks Leonard


Re: Repairing my Tektronix 454 oscilloscope need some advice

Victor
 

Albert,

Thank you for your comments.
I check again the CRT circuit and fuse F1437 is ok, the capacitor C1437 is new (I have change it last week) and Q1430 is ok also. Nevertheless I believe something is wrong on the CRT circuit. I measure voltage on Q1414, Q1413 and Q1423 and some voltages are not as the indicate on the manual... transistors has been tested and are on the specs,so may be some diode or resistance is bad....
Unfortunately, during my investigation I face another issue. The Line EMI filter just dead. So I'm looking for a part that can be installed in the exiting space,and then I can restart my circuit test.

Regards,
Victor


Re: DC508A Frequency Range

 

Hmm...would like to know as well.
I have a DC505a counter, but went with an HP5386A for bigger range afterward. Most of my older HF gear to 3Ghz is combined Tektronix & HP/Agilent. RiGOL for the newer 'daily use' stuff, a bit more user friendly and portable.


Re: 5116+5D10 intensity problem

Harvey White
 

You definitely want to look into one of two things, either bad/reduced high voltage (symptoms would be magnified deflection because a slower electron stream is easier to deflect), and then the cathode/grid bias, but right now, I'm betting on the high voltage.

I wouldn't change the horizontal or vertical gain, but I'd check the outputs of the amplifiers for normal signal levels.  I seem to remember that when the 5000 series was mentioned, there may have been some problems with an epoxy coated HV transformer, which may need to be replaced.  However, I'd check the HV oscillator circuit to see what's going on there.  If, for instance, there is an HV multiplier block (possible), feeding a separate accellerator, then failure of that block causes the image to bloom.

I'd suggest doing a search on the group archives for scope HV problems, which shows the steps you can take to troubleshoot the system.   You do need an HV probe.  It should be specified to work with the meter impedance you have, since it's a 1000 to 1 high voltage divider using the meter itself as the lower part.  10 meg meter needs 9990 meg resistive divider.

You might want to check the discussions on those, too, for additional information

Harvey

On 2/16/2020 2:46 AM, Yeun-Jung Wu wrote:
Hello Harvey:

Since the intensity went down in recent event it never came back. What this 5116 did after turned on was nothing on the screen, even if the intensity control knob was turned fully clockwise. I can tell it was powered on only when scale graticule illumination was fully on.

I guess turn down the vertical and horizontal gain would shrink the display to normal siize. This couldn't be a cure since most important task is to restore a visible trace in normal viewing condition. Once the intensity problem was solved the graticule scale would be normal again.

I did not have any other 5000 series plug-in's. I bought this broken 5116+5D10 with smashed LCD color shutter a few years ago and fixed 5D10 digitizer.

I up load three photos under the file name 5116. Signal to vertical amplifier was interesting: an old video game?

Regard,

Yeun-Jung Wu



Re: DS1742W-120 replacement adapter?

Tom B
 

Thank you.  That looks like a perfect solution.  I really like the idea of being able to change the battery.

Is anybody selling these boards?

Tom

On 2/16/2020 5:23 AM, Jay Walling via Groups.Io wrote:
Given that the Dallas DS1742W-120 is no longer available (excluding Chinese fakes), does anyone make an adapter board to use a more modern chip like the DS1744?
Yes.
https://urldefense.com/v3/__https://www.eevblog.com/forum/repair/tds3014-adventures-(seeking-75-75mhz-oscillator)/msg2766224/*msg2766224__;Iw!!KfGNmQmE!yGkfz7RRa63jEAJiomejYByJDC2uQCzVhb8FbMtFsaBNYgGxG6fKsPUx_m1q$


Re: DS1742W-120 replacement adapter?

 

Given that the Dallas DS1742W-120 is no longer available (excluding Chinese fakes), does anyone make an adapter board to use a more modern chip like the DS1744?
Yes.
https://www.eevblog.com/forum/repair/tds3014-adventures-(seeking-75-75mhz-oscillator)/msg2766224/#msg2766224


Re: 5116+5D10 intensity problem

Yeun-Jung Wu
 

Hello Harvey:

Since the intensity went down in recent event it never came back. What this 5116 did after turned on was nothing on the screen, even if the intensity control knob was turned fully clockwise. I can tell it was powered on only when scale graticule illumination was fully on.

I guess turn down the vertical and horizontal gain would shrink the display to normal siize. This couldn't be a cure since most important task is to restore a visible trace in normal viewing condition. Once the intensity problem was solved the graticule scale would be normal again.

I did not have any other 5000 series plug-in's. I bought this broken 5116+5D10 with smashed LCD color shutter a few years ago and fixed 5D10 digitizer.

I up load three photos under the file name 5116. Signal to vertical amplifier was interesting: an old video game?

Regard,

Yeun-Jung Wu


Re: 2465B Option 05 + 06 (TV/CTT)

cldaves@...
 

Chuck, I like your value system... it really does put things in perspective. 😝


Tektronix 2794 / 2756P Wanted

MARC CHRISTIAN
 

Dear Tektronix Group - Any Member have Tektronix 2794 or Tektronix 2756P For Sale ?

Regards Marc Christian


Re: DC508A Frequency Range

 

Hi Gary,
The DC508A and every frequency counter works down to almost DC limited by the duration of the period between measurements. A 1sec measurement period can measure to 1Hz. A 10 sec period can measure down to 0.1Hz. And so on. There is no lower limit. Without a long enough period you won't get any resolution unless you have a reciprocating counter.
For HF you will almost always use 50 ohm impedance. For low frequency work 1Mohm is more typical.

The manual clearly states the resolution enhancement circuitry only works between a certain audio frequency range. I don't recall the range off the top of my head. The answer is DEFINITELY in the service manual.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Gary Robert Bosworth
Sent: Saturday, February 15, 2020 6:02 PM
To: TekScopes@groups io <TekScopes@groups.io>
Subject: Re: [TekScopes] DC508A Frequency Range

Thank you Bruce. I already had the Operator's and Service Manuals. The specifications state that the 508A will work from 100MHz to 1.3GHz but does not state exactly how low it will work. It appears that there is a high-pass filter that passes frequencies above 100MHz, but I was hoping someone knows if the counter will readout at 50MHz without the error LED coming on. It is not made crystal clear. I have been coping with specsmanship since 1964.

Gary

On Sat, Feb 15, 2020 at 2:47 PM Bruce Atwood <atwood.1@...> wrote:

See http://w140.com/smb/DC508A_SM.pdf page 1-1.



--
Gary Robert Bosworth
@grbosworth
Tel: 310-317-2247





--
Dennis Tillman W7PF
TekScopes Moderator