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Re: 2465 Ch1 attenuator repair question

saipan59 (Pete)
 

Thanks for the comments so far!
As for knobs: I already played with them, and they all came off easily. One has a piece missing from the plastic 'flange' down inside the knob, but it still stays in place on the shaft. There are no metal clips or parts associated with the knobs - they are just a simple press-fit on the specially-shaped shafts.

I will go ahead and attempt the attenuator removal and repair, then report back.

Pete


Re: crushed walnut shells and Tek 500 series scopes

Roy Thistle
 

On Fri, Jan 15, 2021 at 11:28 PM, ditter2 wrote:


sandblasting scopes with crushed with crushed walnut shells
There are different "media" used in "sandblasting booths:" glass beads, silicon carbide, steel shot, aluminum oxide... and walnut shells.
Media usually come in grades... from fine to coarse. You can get walnut shells in 8/12, 30/100 and so on.
Walnut shells are called "soft shot"... but, you can still strip top coat paint with them.
The walnut shells are usually black walnut... of which the U.S. has a great preponderance: black walnut grows wild... and the nut is very hard to crack... so there are lots of them that never get hulled... and can be processed into grit.
Usually the media/shells are mostly blown away inside the booth... for reuse... after it impacts on the item being cleaned. (There is a lot of circulating air, in most booths.)


Re: 2465 Ch1 attenuator repair question

Chuck Harris <cfharris@...>
 

Ok, that makes me feel silly...

I have removed the thimble from those pots a hundred times,
and it never occurred to me that I could use that characteristic
to my advantage.

Live and learn.

Thanks Ozan!

-Chuck Harris

Ozan wrote:

I added a photo album "2467B Bezel removal" that shows how bezel can be removed without pulling the knobs. It is not necessary and most likely knobs will be damaged (or danger of heat damaging the bezel).

https://groups.io/g/TekScopes/album?id=259435
---
Ozan






Re: 2465 Ch1 attenuator repair question

Chuck Harris <cfharris@...>
 

If you don't pull the knobs, you don't remove the bezel.

I don't think there is enough flex in the bezel to allow
it to bend out of the way of the CH1 and CH2 modules..
But even if there is, it would probably be a sketchy affair.

If you want to remove the knobs without breaking them, use
a pair of needle nosed pliers... whose tips are no bigger
in diameter than 1/32". Position those tips underneath the
knob skirt along a diametrical line parallel with the bezel
edge. Using the bezel edge as the fulcrum, gently pry the
knob off.

I have never broken a knob that way.

-Chuck Harris

Ozan wrote:

One recommendation is not to pull the knobs below CRT during bezel removal (ignore step 5 in A5 removal). Over time plastic becomes brittle and every knob I tried cracked. It turns out the knobs slide off with the bezel just fine. I can send you pictures if this is not clear.
Ozan






Re: Coketron - the "Real" Story from Peter Keller :) :) :)

Chuck Harris <cfharris@...>
 

Dumet wire was designed to nearly perfectly match the expansion
characteristics of leaded flint glass. The wetting of dumet
is handled by plating the metal with copper, which wets glass
very nicely. It also gives the seal area the characteristic
pinkish orange color.

I am not certain, but I think I recall that Dumet comes from a
contraction of the words dual and metal.

-Chuck Harris

Roy Thistle wrote:

On Fri, Jan 15, 2021 at 09:53 AM, Jeff Dutky wrote:


I suppose that the glass used for the envelope has specific material
properties to make a good seal around the metal pins, or something similar)
The coefficient of thermal expansion, of the glass, has to sufficiently match that of the material to be embedded in the glass, or joined to the glass. And, the molten glass has to be able to wet it. Many/Most? CRTs, and vacuum tubes, used Dumet wire for the glass to metal seals.
I don't find this information mentioned in Peter's book; but, it is widely discussed, in other sources.






Re: Coketron - the "Real" Story from Peter Keller :) :) :)

Chuck Harris <cfharris@...>
 

Fundamentally, the only problem is we don't know
what type of glass was used for the coke bottle, and
what type of glass was used for the 1EP1. Most likely
the 1EP1 is a laboratory grade of leaded flint glass,
and the coke bottle isn't.

So, if you fuse the two together, there will be subtle
differences in the expansion characteristics of each
glass, leading to a crack, when the glass is cooled
sufficiently below the temperature where the glasses
were fused.

There are several ways to work around this problem.

The easiest would be to use an intermediate material
between the two glasses, such as the lead frit that
is used to "solder" the screens of CRT's to the funnel
section. Lead frit is a very highly leaded glass, that
can contain as much as 50% lead. The lead frit melts
at a much lower temperature than ordinary glasses, and
forms a very strong seal. It is used for things like
mating leaded glass funnel sections to CRT screens.

Indium solder can also be used.

Another way, would be to make a cylindrical center metal
section out of stainless steel, and form a "housekeeper"
seal on each end that is fused to the glass.

Housekeeper seals are made on a lathe by turning the
edge of the stainless steel cylinder into a long slow
tapering knife edge... like you would need if you were
planning to use the stainless steel cylinder to cut
disks out of leather.

Because the edge that is bonded to the glass is only
1-1.5 thousandths of an inch thick, and the taper is about
3/8 inch long, the stainless will stretch to adapt to the
differential expansion characteristics of stainless and
glass.

They can be effectively done for diameters in the 1/4 to
2" range.

These techniques are well known, and certainly not beyond
the capabilities of any technical glass blower.

-Chuck Harris



Roy Thistle wrote:

On Fri, Jan 15, 2021 at 10:33 AM, Tom Lee wrote:


Join the Coke bottle to one end of the cylinder, the gun to the other
Then one would have two seals to de-stress... the vacuum is pulled by removing the base, on the electron gun assembly... and attaching glass tubing there to pull the vacuum.
I know it is supposed to be funny... or a joke... but, the Coketron depicted in Peter's book is a prop... and we don't know for certain if any Coketron like that ever worked, or if one did... for how long...or what kind of external support was required.
We do know these were fabricated at a Tektronix CRT lab, employing specialized skills and technology that are now mostly lost.
Anyway, it isn't funny when people get it into their heads to "make" something like a Coketron... and fruitlessly waste several 1EP1s or other working miniature CRTS, to do a YouTube video. There are people out there that don't understand the joke.






Re: Missing knob for Tek 576

Jean-Paul
 

Had similar problem on AC, NPN PARIS knobs on my 576, found perfect substitutes from old junked TEKTRONIX 7000 scope plug-ins.

Jon


Re: P6137 scope probe repair

Jean-Paul
 

Hello again

Doubt if TDR or bridge gives any useful information

Just look carefully and try to flex every inch, you can find a mechanical or visible flaw, often near the ends.

It is easier to buy some new ones than to find the cable.

Bought many over the years via epay about $35-70 ea, mostly in liked newsletter condition.

Bon courage

Jon


Re: P6137 scope probe repair

Lawrance A. Schneider
 

On Sat, Jan 16, 2021 at 03:48 AM, Jared Cabot wrote:


Predictably, the center conductor on the cable is open circuit.
I believe you could use a nanoVNA to locate the break.

larry


Re: P6137 scope probe repair

Jared Cabot
 

I have a small TDR unit, but it i mainly for longer runs, I'll give it a go though. I also have a 4276A LCZ meter I can use though.

Using the 4276A, I get 3.3pF at the scope end, and the probe end is not really able to be read properly, the 4276A freaks out a bit but shows 0.02nF, and my 34461A goes out of range.
I remember reading that oscilloscope probe cables are deliberately resistive or something, maybe that could be causing the weird reading. If that is the case, I would assume that the break is near the scope end of the cable as there isn't enough of the cable there to throw readings off.
It would make sense too, if the cable was pulled while attached to the scope, that is where the strain would likely be concentrated.

Sound like a reasonable assumption?


Missing knob for Tek 576

Dave S.
 

Hi guys,

im looking for a missing knob of the trace positioning (see pic below)

https://i.gyazo.com/8e018f12acdef8d57bc2c949135d350f.jpg

The original part number is 366-1027-00, unfortunately i cant find it via google

Maybe someone got a used one (id pay for it ofc)

BR,
David


Re: P6137 scope probe repair

Tom Lee
 

The cable is replaceable (I think you've seen this already, since you've disassembled it). The hard part is finding a good cable at a reasonable cost.

Does the cable show any obvious signs of damage?

If the break is at or near one of the ends, that's fixable. If it's somewhere near the middle, it's probably a lost cause, if you want to maintain a clean response.

If there are no visible cues as to where the break is, you've got a little extra work to do. If you have access to a TDR, you can pinpoint the location of the break easily. In the absence of a TDR, you can still find the location with surprising accuracy from two good capacitance measurements: Suppose the total cable length is L, and one segment is of length x1 and the other is x2. If the capacitance looking into x1 is C1, and that into x2 is C2, then x1 = L [C1/(C1 + C2)]. If you're lucky, you'll find that one of the capacitances is very much smaller than the other, indicating that the break is indeed at or near the ends.

All this assumes, of course, that you have definitely isolated the cable in determining that the cable, and not something in the compensator box or connections to it, is truly broken.

Good luck!

-- Tom


--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 1/16/2021 00:48, Jared Cabot via groups.io wrote:
Hi all,

I recently picked up a P6137 scope probe for a song and thought I'd try my luck.
Predictably, the center conductor on the cable is open circuit..... Is there any way to repair or replace this cable with a new one? I have it apart now, but is there some sort of cable I can use as a replacement?


Thanks!
Jared.




Re: 2465 Ch1 attenuator repair question

Ozan
 

I added a photo album "2467B Bezel removal" that shows how bezel can be removed without pulling the knobs. It is not necessary and most likely knobs will be damaged (or danger of heat damaging the bezel).

https://groups.io/g/TekScopes/album?id=259435
---
Ozan


P6137 scope probe repair

Jared Cabot
 

Hi all,

I recently picked up a P6137 scope probe for a song and thought I'd try my luck.
Predictably, the center conductor on the cable is open circuit..... Is there any way to repair or replace this cable with a new one? I have it apart now, but is there some sort of cable I can use as a replacement?


Thanks!
Jared.


Re: 2465 Ch1 attenuator repair question

 

I've been told that you can remove those push-on knobs by gently heating them (e.g. with a hair dryer) before you try to remove them. The heat supposedly softens the plastic enough that it will bend but not break during removal.

I broke the internal retaining clips on one of those knobs on my 2236 trying to remove it, and have been working up the courage to try the hair dryer removal method on a parts mule.

I haven't tried this yet, so take this as hearsay rather than sage advice.

-- Jeff Dutky


Re: 2465 Ch1 attenuator repair question

Ozan
 

One recommendation is not to pull the knobs below CRT during bezel removal (ignore step 5 in A5 removal). Over time plastic becomes brittle and every knob I tried cracked. It turns out the knobs slide off with the bezel just fine. I can send you pictures if this is not clear.
Ozan


crushed walnut shells and Tek 500 series scopes

ditter2
 

Dennis – I hope you don’t consider this off topic. It is not on repairing a classic Tek scope – but an aspect on how they were made.

After reading the posting from the Peter Keller on the Coketron, it reminded me of another unique Tek process few know of, which I would like more details on The process is “sandblasting scopes with crushed with crushed walnut shells”.

Those who have seen the insides of any 500 series era Tek scope know the beauty of the ceramic strip construction hidden under the covers. The passive components and wiring harness are interconnected on a series of ceramic strips, with notches each containing a shiny fillet of silver bearing tin-lead solder. Have you ever wondered how Tek removed the solder rosin from the ceramic strips after assembly? There is no rosin showing on the ceramic strips, unless the scope has been repaired after it left the factory.

The solder rosin was removed from the ceramic strips with an air propelled abrasive cleaning method using – crushed walnut shells. It is similar to sand blasting, but with higher volume, lower pressure and lower velocity air. I was never able to see this in action while I worked at Tek, but many of the older engineers I worked with attested to the use of this process. (When I joined in 1978, Tek was still finishing up producing the last remaining type 1A1 plug-ins for a large long term contract with the US Army. I toured the production area, but did not see the cleaning operation at the time.) I know that the Tek Materials catalog had a Tek part number listed for crushed walnut shells used for this purpose. I was told that some delicate components, such as the beam lead Tek made TDs, special rubber covers were placed over the component prior to cleaning to prevent the lead being cut by the blast.

As I have never seen the operation, perhaps another member who has can answer these questions:
What was the size of the blast gun / nozzle?
How were the crushed shells removed from the scope after cleaning – vacuum cleaning?

Steve


Re: Tektronix 492BP

 

I tapped the boards and I got it to work the calibration sequence. I just cant get hte upper bands just to 21GHz. How can I display the upper bands?


Re: Coketron - the "Real" Story from Peter Keller :) :) :)

Roy Thistle
 

On Fri, Jan 15, 2021 at 09:53 AM, Jeff Dutky wrote:


I suppose that the glass used for the envelope has specific material
properties to make a good seal around the metal pins, or something similar)
The coefficient of thermal expansion, of the glass, has to sufficiently match that of the material to be embedded in the glass, or joined to the glass. And, the molten glass has to be able to wet it. Many/Most? CRTs, and vacuum tubes, used Dumet wire for the glass to metal seals.
I don't find this information mentioned in Peter's book; but, it is widely discussed, in other sources.


Re: Tektronix 214 Storage Scope

ditter2
 

There is a safety issue with modifying these 200 series analog scopes with either external batteries/power supplies, or installing BNC connectors to allow use with other standard scope probes. These scopes are double insulated. So adding a BNC connector with exposed “ground” or external batteries can expose the operator to the elevated voltage the scope is floating on, with risk of electrical shock.
As Dennis replied, there have been several postings on alternatives for the single ‘A’ size NiCd cells in the original battery packs. A simple no fuss mod is to replace with nickel metal hydride cells. Some searching on the Internet will come up with vendors selling the odd single 'A' size cell Tek used in these scopes. You can substitute without changing the charging circuit, however it will take a long time to fully charge with the lower charging current the NiCd cells could handle. But on the upside, the run time is considerably longer as the Ni metal hydride cells have nearly 10x the mA/hour rating of the original NiCd cells. A bit more work is required to update the charging circuit for faster charging. A good design will incorporate a “smart” charging IC, to prevent overcharging, as well as disconnect the battery from the load when the voltage gets too low – the cause of dry cell leakage.

Steve

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