Date   

Re: Recreating an old board for the 7854

Zentronics42@...
 

I have uploaded iteration 3 of the test card. I do need to pour the fill zones on the board but changing the resister to THT parts helped with the routing immensely. I also bumped up the thickness of the traces and I also took care with the 90 degree corners. If the board looks good and there is no gross mistakes I will clean up the silk screen, get a few boards spun, and move on to testing.


File /7854/067-0912-00 Recreation/Tektronix 7854 test card rev 3 Possable Prototype.pdf uploaded #file-notice

TekScopes@groups.io Notification <noreply@...>
 

The following files have been uploaded to the Files area of the TekScopes@groups.io group.

By: Zentronics42@...

Description:
This is iteration 3 of the test card possible board to spin


Re: Curious behavior of a CRT

Albert Otten
 

Interesting. Can you find that document and link to it? Glass is a good
insulator inside of vacuum. Outside, not so much, due to surface effects.
Ed
Perhaps TekScope 1969 June, page 14 under "CRT considerations"? Static charge on CRT-gun support rods etc. Same remedy.
PDF available at Tekwiki under "TekScope".
Albert


Re: Tunnel diode capacitance test

Miguel Work
 

:) don´t worry Albert, I have made a little tunnel pulser box to test rise time. I will compare 10mA tunnel diode, AI301G and AI201A. At the moment the first one (<50pF) yields 1,1nS in a 350pS sistem. I will upload some photos. I have replaced the output tunnel diode in a 7T11 with the AI201A, i don´t have more original tektronix diodes.


Re: Curious behavior of a CRT

Ed Breya
 

Interesting. Can you find that document and link to it? Glass is a good insulator inside of vacuum. Outside, not so much, due to surface effects.

Ed


Re: 7704A (et. al.) Inverter Regulator Question

n4buq
 

Yesterday, I discovered that C3150 was not bad. I lifted one leg and it checked good which really didn't surprise me as I don't think dipped silver micas have a reputation for going bad like that. With U3105 out of the circuit, I didn't think there would be anything else that would have affected an in-circuit test; however, apparently that was a false assumption because the +7.5V "rail" goes to quite a bit more places than I had first thought. I notice that other caps also check very low (30pF or so vs their designated values) in circuit and they all may be related to the same sort of in-circuit testing issue.

I'm still waiting on parts but hopefully, once I get those, I can make better progress on this PS.

Thanks for listening...
Barry - N4BUQ

----- Original Message -----
From: "Barry" <n4buq@...>
To: TekScopes@groups.io
Sent: Monday, September 13, 2021 1:29:59 PM
Subject: Re: [TekScopes] 7704A (et. al.) Inverter Regulator Question

I just checked those with my component checker (without U3105 plugged in as I
wasn't sure what effect that might have) and, yes, I have several bad
tantalums so those will be replaced. Oddly, C3150 is bad (measures about
32pF). I really didn't expect that one and, to be honest, thought the
smaller tantalums would have been okay. I was wrong.

I wish I'd realized all this when I had the board out. Some of those can be
replaced without having to remove the board but some, particularly C3150,
may not be possible.

This poor power supply has had a rough time of it...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@...>
To: TekScopes@groups.io
Sent: Monday, September 13, 2021 12:55:11 PM
Subject: Re: [TekScopes] 7704A (et. al.) Inverter Regulator Question

Barry,

Goran is right about that area. VR3147 being open will throw the circuit
off.
C3127 and C3129 are marked ,1mfd. Some models use 1mfd in this place. I
have
replaced mine with the 1mfd 63V film types because the ESR of the originals
was too high causing too much ripple and low B+. After replacing the parts,
the B+ voltages at the pins on the 0067 IC were correct. These parts can be
checked while the parts you have on order are being shipped. I also
replaced
the 1 and 2mfd electrolytics on the inverter board with film types of a
higher voltage. The originals were bad in mine.

Mark






Re: Curious behavior of a CRT

bill koski
 

Glass is a great dielectric material.
I've seen the 2nd anode on picture tubes, Especially old set with tube rectifiers, still have a good charge days and even weeks after the last time it was turned on.


Re: Tunnel diode capacitance test

Albert Otten
 

Sorry Miguel for wrong spelling of your name in my previous message. Albert


Re: Tunnel diode capacitance test

Albert Otten
 

I think Michael merely wants to know the capacitances for comparison with specs of the original diodes. In our circuits these diodes are used for switching. It seems that the capacitance during switching is more or less constant and is shown in the specs.
I would measure switching characteristics (rise time and more) and then calculate (in crude ore more refined approximation) the capacitance. For instance the RCA 1963 manual (link at Tekwiki "Tunnel diodes") approximate relations when the load can be neglected.

Albert

On Wed, Sep 15, 2021 at 05:47 AM, Ed Breya wrote:


I'd suggest that you don't worry about it. There will be some fixed holder
capacitance due to the package, but the rest is non-linear, and depends on
bias voltage and circuit conditions. If there are any specs, they would have
to be at certain conditions, that you could probably replicate. To make decent
measurements, you have to keep the AC signal test voltage as low as possible
(like a few to tens of mV) to avoid junction activation and effects. A VNA
probably has enough dynamic range to easily handle it with small test signals.
The bridge may work too, if it can operate well at low enough voltage.

Ed


Curious behavior of a CRT

Morris Odell
 

My friend who is restoring a 547 was experiencing a lot of trouble with trace distortion. On switch on the trace was not straight, was tilted and appeared non linear. The geometry and trace rotation controls did not change things. Substitution of a known good CRT didn't seem to make any difference and the fault persisted when the Y deflection plates were shorted thus eliminating the VA as the source of the problem. It was starting to look like a faulty CRT even though it was extremely unlikely that two CRTs had the same problem. Eventually he referred to a Tek publication on scope servicing that mentioned the possibility of static build up on the glass supports inside the CRT. It advised curing the problem by deflecting the beam around but off the screen, with the intensity turned to max. The intention was to dissipate the static charge through the beam. It was successful and the scope now works just as it should!

I've been playing with electronics and scopes for more than 50 years but this is a new one for me. I was amazed that static charges could have persisted on the internals of the CRT for days or even weeks and wonder if there is some other explanation. Has anyone else had the same experience? I'd be interested to hear from anyone who knows something about this.

Thanks,

Morris


Re: Tunnel diode capacitance test

Ed Breya
 

I'd suggest that you don't worry about it. There will be some fixed holder capacitance due to the package, but the rest is non-linear, and depends on bias voltage and circuit conditions. If there are any specs, they would have to be at certain conditions, that you could probably replicate. To make decent measurements, you have to keep the AC signal test voltage as low as possible (like a few to tens of mV) to avoid junction activation and effects. A VNA probably has enough dynamic range to easily handle it with small test signals. The bridge may work too, if it can operate well at low enough voltage.

Ed


Re: Tektronix 067-1338-0x calibration step generator for SD-series sampling heads

emissionlabs
 

I see what you mean. Yes 20ps is really fast. I am sure that is usefull for some cases. The 33120A can never do that.

I checked what the 33120A could do with my SC504 scope, which is 80mHz. The 33120A can repeat the signal at 1mHz. I could verify the 0.1uS/div with it. 10 repetitions, and 1/5 of the last division too slow. So 2% too slow. I could not verify the fastest range 50ns/div any more. But at any lower range it is 2% too slow as well. So just when I make no mistake, with the 33120A I could see this 80mHz scope time base is 2% off.


Re: 577 D2 Display Issues

@gmilliorn
 

Thanks for the suggestions everyone, I will start with cleaning the soot.

Is this the storage version?
The D2 is the non-storage. The front-panel intensity pot is very linear, delivering -30..30V to
the HV board. But the intensity range trimmer under the shield is hard to turn and acts oddly,
I wonder if it is contaminated with soot just like everything else there.

I hadn't thought of soot as conductive, though I guess that's obvious in hindsight. The HV adjust
is also in the sooty area, and HV range is also not working.


Re: Tektronix 067-1338-0x calibration step generator for SD-series sampling heads

John Gord
 

The main feature of the Tektronix 067-1338-0x is the step rise time of under 20ps. The 33120A arbitrary waveform generator is much, much slower.
--John Gord

On Tue, Sep 14, 2021 at 07:38 AM, emissionlabs wrote:


I used an Agilent 33120A arbitrary waveform generator instead if a time mark
generator. It costs less, and you can use it for many other things too. I
don't know of there are any important differences which make the 33120A
impossible to use, but I was not aware. So I just did it, and it worked
fine. The signal you see is from the 33120A.

https://www.jacmusic.com/techcorner/INSTRUMENTS/TEKTRONIX/5113-Scope/Cardiac2-250.jpg




Re: Tektronix 067-1338-0x calibration step generator for SD-series sampling heads

emissionlabs
 

I used an Agilent 33120A arbitrary waveform generator instead if a time mark generator. It costs less, and you can use it for many other things too. I don't know of there are any important differences which make the 33120A impossible to use, but I was not aware. So I just did it, and it worked fine. The signal you see is from the 33120A.

https://www.jacmusic.com/techcorner/INSTRUMENTS/TEKTRONIX/5113-Scope/Cardiac2-250.jpg


Tunnel diode capacitance test

Miguel Work
 

I have a bunch of russian tunnel diodes, I want to test his capacitance. Any suggestion?
I have a working 7S12 reflectometer, a 7s14, a 500Mhz TDS 5054 scope, a nanovna V2 +, a waynekerr 6425 bridge too. Bridge "only" arrives to 300khz


Regards!


Re: 7T11 diode tunnel destroyed connecting a 15pF 1:10 probe?

Miguel Work
 

Hi Tom

Yes, the output tunnel diode was "working", but it haves >100 ohms resistance

Arm diode is ok, but is diferent kind, is a 10pf, de output is a <5pff

When I first tested operation I don´t have output in trigger otuput, so I went directly to test TD operation with probe.

Output TD was bad, open, so I replaced it with the same diode. It worked but only for a few minutes, bias pot was at max, but I don´t belive that this was the cause of the problem,

Some times it has a 100 ohms resistor, others is open, the second diode that I replaced

Then I have replaced it for a russian AI201A 3.5pF 10mA GaAs and now is working

So, I suspect that the capacitance probe has some efect destroying the TD diode. Tunnel diode is connected to -15V, so when I connect the probe it charges 15pF, capacitance probe, through the tunnel diode.


Re: "mottled effect" on anodized front panel

Tom Norman
 

Thanks Chris for the correction. I went and took a look at my supply of Novus and it was the #2 that I used, just for confirmation.

Tom


Re: 502A Dual Beam Oscilloscope on Shopgoodwill

Clark Foley
 

Now the cat’s out of the bag!


Re: 577 D2 Display Issues

Andy Warner
 

If the intensity low-high-low thing persists after you clean the soot off,
you may have a weak tube. I assume this is as you move the intensity
control clockwise.

Look for a 5110 scope, they have the same tube, with the telltale graticule
arrows in the lower left corner. I was in the same boat as you a few months
ago, but was able to find a 5110 with a good tube, so do not lose hope.

On Mon, Sep 13, 2021 at 15:07 <gmilliorn@...> wrote:

I've been trying to restore a 577 D2 that had several problems. The
previous owner(s) hacked up the -12V supply and the regulator was floating,
unheatsinked. The 200V fuse was blown (cautiously replaced, no issues
so far), sticky switches (cleaned), excessive ripple (recapped). After
all that I got the stairstepper working and get the mostly correct display.

There's a few odd issues though:
* Every 1-5 seconds there's a brightness flash on the traces. There's
nothing seen on power supplies or main boards that correlates.
* Focus is sharp but intensity ranges from low-high-low.
* HV is limited to -3362V max (or min?), but should range -3270..-3570.
* There's black soot on the inside of the HV shield as well as the back
of the yoke connector (I can see someone's thumbprint). Not sure
how that happened, but it was in two physically separated areas.

So it mostly looks like an HV issue, but that odd flash makes me worry
it could be the tube. It doesn't appear to have been replaced, despite
the thumbprint. Does any of the above point to one or the other?

Thanks,
Gary





--
Andy

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