Date   

Re: Washing Oscilloscopes

Stan or Patricia Griffiths <w7ni@...>
 

Great story, Dave. I have to admit, you are the first one to save a
transfomer that way that I know of. Good job.

Stan
w7ni@easystreet.com

david_wise@phoenix.com wrote:

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
Usually, I am in complete agreement with Dean on these scope
maintenance issues but I really have to take exception to
this one about being too picky about what water you use to
wash your scopes. Not all city tap water is the same and some
water that you would drink without hesitation will DESTROY a
perfectly good Tektronix power transformer. If found this out,
big time, when washing scopes in San Diego, CA.
[snip]

Most of the time, the leakage in the power transformer is caused by
a small amount of water with conductive ions getting inside the
transformer itself and depositing the ions there. These ions form
a conductive path to ground inside the transformer and I have NEVER
seen a transformer recover from this, despite repeated rinsings,
etc, etc, etc to try to remove the conductive path to ground. The
official Tektronix answer was to replace the transformer with
a new one.
[snip]

I wash scopes here in Oregon now and I use straight, untreated tap
water with no problems. This is probably more than you EVER wanted
to know about washing scopes . . .
Dave Wise here. A few years ago I washed a 535 in Portland Oregon
with the transformer in place, and saw CRT heater winding leakage
afterward. I saved it. Maybe I got lucky or caught it before it
became irreversible. (After all, I only ran it for a moment.)
I went to a local bottled water place and told them what I needed to
do. They handed me a milk jug with "1000Meg" or something similar
scrawled on it and wished me luck. I put the tranny in a big baggie,
added some water, sealed it, swished a while, dumped, and repeated.
When I'd used up all the water, I blew it with compressed air, let it
dry for a couple of days, put it back, and it's been fine ever since.

Regards,
Dave Wise
535
535A
545 x 2
547
CA, D, G, H, L, Z, 1A4

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Re: Washing Oscilloscopes

Stan or Patricia Griffiths <w7ni@...>
 

Hi John,

Pretty much any medium I want including, for example, CD ROMS. Just so you
don't misunderstand, Tek granted permission for ME to copy their stuff and not
other people . . .

Stan
w7ni@easystreet.com

John Miles wrote:

Neat! When you're able to talk about it, I'd be curious if the permission
extends to making electronic copies or just paper ones.

-- jm

By the way, the readers of this list will be interested to know that I
have
obtained WRITTEN PERMISSION from the Tek Legal Department to make copies
of
Tek copy righted materials that Tek no longer makes available for sale. I
plan to use this permission but it is too early to talk about it at this
time. Stay tuned . . .

Stan
w7ni@easystreet.com


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Was 7503 Now metal migration

Doug Hale <doughale@...>
 

ICs use aluminum as the interconnect between the devices in the substrate. Aluminum is a relatively soft metal.
The way ICs get denser is to shrink device geometry's and make smaller interconnects. There is a limit
as to how small the aluminum geometry's can go, partially due to metal migration. That is why it has been
in the news that IBM has developed the processes to use copper which is harder (migrates less) under
the same conditions. It can, therefore, be made smaller than aluminum which yields smaller parasitic
capacitance and higher speeds.


Doug


Manual Copying

jrlaw@...
 

Thursday, October 18, 2001

Dear Stan:

Congratulations on the breakthrough with Tek legal. I hope that
the dialogue and debate on this group made a constructive
contribution to their decision.

I know that all of are waiting with bated breath to hear the
details and, particularly, how you plan to utilize this very sensible
permission. If I can help at all from a legal perspective (strictly
as a volunteer and without liability as we love to say!), please let
me know. My office email is above but my home is now
jonescollins@sympatico.ca .

Thanks from all of us

Richard B. Jones


Re: Washing Oscilloscopes

Michael Dunn <mdunn@...>
 

At 2:23 PM -0700 2001/10/18, John Miles wrote:
After
rinsing with the wand on the normal setting, I switched to the "spot-free
rinse" mode, which I surmised was deionized or at least reasonably-filtered
Or perhaps something similar to the stuff you use in a dishwasher rinse cycle??? Speaking of which, does anyone know what the properties are of that stuff? I can't imagine it's something you'd want to use when cleaning electronics...?

Michael


Re: Washing Oscilloscopes

John Miles <jmiles@...>
 

<anecdote>

After my dad (K5CX) passed away some years ago, I inherited his old HP 6284A
bench supply, a nice CV/CC model. Dad was a heavy smoker and the power
supply was completely saturated with tar residue, inside and out. Because
it worked perfectly, I couldn't stand to throw it away, but it was clearly
unusable as it was. You could probably get cancer just from spending half
an hour in the same room with it.

Figuring I had nothing to lose, I stripped the supply down to the last nut
and bolt and took the pieces down down to the nearest car wash bay. I began
by blasting it with high-pressure soap and water, holding with the wand far
enough away to avoid physically damaging parts on the PCB but otherwise
showing no mercy to the board, transformer, heat sink, and panels. After
rinsing with the wand on the normal setting, I switched to the "spot-free
rinse" mode, which I surmised was deionized or at least reasonably-filtered
water delivered at a much lower pressure. Ten minutes or so of this
treatment, and the power supply looked like new. I took the pieces home,
dried them in my oven for several hours at around 130F, put everything back
together, squirted some WD40 in the controls, trimmers, and switches, and
powered it up.

No smoke -- everything seemed to work perfectly! Voltage and current
regulation was spot-on, so I put the supply on my bench and forgot about it.
Nothing ventured, and a great piece of test equipment gained. Free lunch,
and all that.

* * *

Fast-forward: one year later. I was fooling around with a high-speed FSK
demodulator circuit. I'd just received a half-dozen MC13155Ds from Newark
at around $8 apiece, following my usual practice of ordering a few more than
I expected to use in my project. At least that was the idea. The trouble
was, it looked like I was going to need all of the chips just to build the
first of two demodulator assemblies, because they kept blowing out on me!
I'd power up the circuit, make some measurements, power down the circuit,
change a resistor or something, turn the power back on, and the MC13155D
would be as dead as Graham Chapman's parrot. Put in a new '13155, power on,
everything's fine again. Power down, make an adjustment, power up, nothing.
Lather, rinse, repeat.

This was something I'd never seen before -- in-circuit static damage? Not
likely, this wasn't even a MOS part. Bad chips or soldering damage? No,
they all worked fine when first installed, and I hadn't burned up an IC with
my soldering iron since the fourth grade. Destructive parasitic? Didn't
see a thing on my trusty 492. Besides, the power supply's current limit was
set to only a few mA, so it ought to be impossible for the chip to draw
enough current to blow up. Finally, it occurred to me that I might be
getting turn-on surges from Dad's old HP6284A, the one that I'd cavalierly
hosed down at the Scrub-n-Suds the year before. I clipped a scope to the
output jacks and flipped the supply on. The trace rose quickly to the
preset level of 5 volts and stayed there, without the slightest hint of
overshoot or ringing.

So, having thus eliminated every possible fault on my end, I resigned myself
to going through my stock of ICs until I found one that actually worked
consistently. I was down to my last MC13155D when it occurred to me to
watch the voltage as I turned the supply OFF.

Bingo. I could only watch in horror as the 5-volt output spiked to the
supply's ceiling of 20+ volts several milliseconds after turnoff, staying up
there for a good 250 milliseconds. Evidently, the supply's voltage
regulator was losing its reference voltage as soon as the transformer's
field collapsed, allowing the entire residual charge in the filter capacitor
to appear at the output terminals. There was no telling why -- I didn't
have a schematic for the supply, which was built in the days when a CV/CC
regulator circuit took about two dozen discrete transistors in multiple
interacting control loops -- but I couldn't imagine that such an evil fault
was present while Dad was using the supply. He lived in the country and had
a lot of time on his hands, and also a lot of guns. That meant that he
would either have fixed the supply, or used it for .22 target practice.

One of these days I'll dig up a schematic and do some troubleshooting... I'm
sure I must have knocked loose a diode or capacitor with all that
high-pressure water, or opened up a trimmer. Until then, the line-operated
relay I put in series with the output terminals will have to suffice. :-)

Moral: don't assume that careless equipment-washing practices are OK just
because you THINK the gear still works fine. Stick to the Tek-approved
practices as outlined by Stan in his book, or risk premature hair loss later
on.

</anecdote>

-- jm

Dave Wise here. A few years ago I washed a 535 in Portland Oregon
with the transformer in place, and saw CRT heater winding leakage
afterward. I saved it. Maybe I got lucky or caught it before it
became irreversible. (After all, I only ran it for a moment.)
I went to a local bottled water place and told them what I needed to
do. They handed me a milk jug with "1000Meg" or something similar
scrawled on it and wished me luck. I put the tranny in a big baggie,
added some water, sealed it, swished a while, dumped, and repeated.
When I'd used up all the water, I blew it with compressed air, let it
dry for a couple of days, put it back, and it's been fine ever since.

Regards,
Dave Wise
535
535A
545 x 2
547
CA, D, G, H, L, Z, 1A4


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Re: Washing Oscilloscopes

Miroslav Pokorni <mpokorni@...>
 

I think that besides the luck, key was low time under power. With some
conductivity between wires you can get electromigration that leaves kind of
conductive path. I have seen that at much lower voltage levels, 5V, in
ceramic decoupling caps. Caps would crack due to thermal stress and washing
would leave residual moisture. Over time, a week to 26 weeks, metal whiskers
would grow and eventually short the cap; in the process, some whiskers would
get burned away when they become conductive enough, while others would get
fused together and form solid short. This problem was run into ground with
help of cap manufacturer, because a customer had concern over high failure
rate.

Regards

Miroslav Pokorni

-----Original Message-----
From: david_wise@phoenix.com
[mailto:david_wise@phoenix.com]
Sent: Thursday, October 18, 2001 12:59 PM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Washing Oscilloscopes

--- In TekScopes@y..., Stan or Patricia Griffiths
<w7ni@e...> wrote:
> Usually, I am in complete agreement with Dean on these
scope
> maintenance issues but I really have to take exception to
> this one about being too picky about what water you use to
> wash your scopes. Not all city tap water is the same and
some
> water that you would drink without hesitation will DESTROY
a
> perfectly good Tektronix power transformer. If found this
out,
> big time, when washing scopes in San Diego, CA.

[snip]

> Most of the time, the leakage in the power transformer is
caused by
> a small amount of water with conductive ions getting
inside the
> transformer itself and depositing the ions there. These
ions form
> a conductive path to ground inside the transformer and I
have NEVER
> seen a transformer recover from this, despite repeated
rinsings,
> etc, etc, etc to try to remove the conductive path to
ground. The
> official Tektronix answer was to replace the transformer
with
> a new one.

[snip]

> I wash scopes here in Oregon now and I use straight,
untreated tap
> water with no problems. This is probably more than you
EVER wanted
> to know about washing scopes . . .

Dave Wise here. A few years ago I washed a 535 in Portland
Oregon
with the transformer in place, and saw CRT heater winding
leakage
afterward. I saved it. Maybe I got lucky or caught it
before it
became irreversible. (After all, I only ran it for a
moment.)
I went to a local bottled water place and told them what I
needed to
do. They handed me a milk jug with "1000Meg" or something
similar
scrawled on it and wished me luck. I put the tranny in a
big baggie,
added some water, sealed it, swished a while, dumped, and
repeated.
When I'd used up all the water, I blew it with compressed
air, let it
dry for a couple of days, put it back, and it's been fine
ever since.

Regards,
Dave Wise
535
535A
545 x 2
547
CA, D, G, H, L, Z, 1A4


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Re: Washing Oscilloscopes

Miroslav Pokorni <mpokorni@...>
 

Hi Dave,

You do not hold a copyright on being a Wise crack? You will not sue me when
I try being a wisecrack.

What you forgot to add to the list after your signature is: 'and owner of
two umbrellas'. That is how oriental monarchs used to sign their names,
listing all their significant earthly possessions.

Regards

Miroslav Pokorni

-----Original Message-----
From: Michael Dunn [mailto:mdunn@cantares.on.ca]
Sent: Thursday, October 18, 2001 1:12 PM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Washing Oscilloscopes

At 7:59 PM +0000 2001/10/18, david_wise@phoenix.com
wrote:
>They handed me a milk jug with "1000Meg" or something
similar
>scrawled on it and wished me luck. I put the tranny in a
big baggie,
>added some water, sealed it, swished a while, dumped, and
repeated.

Shake and Bake.


>Regards,
>Dave Wise
>535
>535A
>545 x 2
>547
>CA, D, G, H, L, Z, 1A4

Neat idea. We should all start doing that. Except
maybe Stan and
a few others ;-) (should it include 7000 stuff too? Nah.
I'll
stick to tube gear)

Michael (list führer)
502A
549
556
1A1 (3x), 1A4, 1A5, 1S1, 3S76

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Re: Washing Oscilloscopes

Michael Dunn <mdunn@...>
 

At 7:59 PM +0000 2001/10/18, david_wise@phoenix.com wrote:
They handed me a milk jug with "1000Meg" or something similar
scrawled on it and wished me luck. I put the tranny in a big baggie,
added some water, sealed it, swished a while, dumped, and repeated.
Shake and Bake.


Regards,
Dave Wise
535
535A
545 x 2
547
CA, D, G, H, L, Z, 1A4
Neat idea. We should all start doing that. Except maybe Stan and
a few others ;-) (should it include 7000 stuff too? Nah. I'll
stick to tube gear)

Michael (list führer)
502A
549
556
1A1 (3x), 1A4, 1A5, 1S1, 3S76


Re: Washing Oscilloscopes

Dave Wise
 

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
Usually, I am in complete agreement with Dean on these scope
maintenance issues but I really have to take exception to
this one about being too picky about what water you use to
wash your scopes. Not all city tap water is the same and some
water that you would drink without hesitation will DESTROY a
perfectly good Tektronix power transformer. If found this out,
big time, when washing scopes in San Diego, CA.
[snip]

Most of the time, the leakage in the power transformer is caused by
a small amount of water with conductive ions getting inside the
transformer itself and depositing the ions there. These ions form
a conductive path to ground inside the transformer and I have NEVER
seen a transformer recover from this, despite repeated rinsings,
etc, etc, etc to try to remove the conductive path to ground. The
official Tektronix answer was to replace the transformer with
a new one.
[snip]

I wash scopes here in Oregon now and I use straight, untreated tap
water with no problems. This is probably more than you EVER wanted
to know about washing scopes . . .
Dave Wise here. A few years ago I washed a 535 in Portland Oregon
with the transformer in place, and saw CRT heater winding leakage
afterward. I saved it. Maybe I got lucky or caught it before it
became irreversible. (After all, I only ran it for a moment.)
I went to a local bottled water place and told them what I needed to
do. They handed me a milk jug with "1000Meg" or something similar
scrawled on it and wished me luck. I put the tranny in a big baggie,
added some water, sealed it, swished a while, dumped, and repeated.
When I'd used up all the water, I blew it with compressed air, let it
dry for a couple of days, put it back, and it's been fine ever since.

Regards,
Dave Wise
535
535A
545 x 2
547
CA, D, G, H, L, Z, 1A4


Re: 7503

mwcpc7@...
 

In a message dated 10/17/2001 6:02:07 PM Eastern Daylight Time, spam@fgm.com
writes:

In DC filaments, this occurs along the entire
unit.

A web search on "filament notching" yields lots of hits,
including these two (both have illustrations). The second
one even mentions that filaments drawing less than 40mA
(i.e. thin filaments on low candlepower lamps) at 1800-2250K
(typical long life lamp temperatures) are particularly
susceptible.
Maybe this explains why putting a diode in series with night light lamps
(which I've done for years) doesn't extend their life any where near much as
I thought it should.

Mike Csontos


Re: Washing Oscilloscopes

John Miles <jmiles@...>
 

Neat! When you're able to talk about it, I'd be curious if the permission
extends to making electronic copies or just paper ones.

-- jm

By the way, the readers of this list will be interested to know that I
have
obtained WRITTEN PERMISSION from the Tek Legal Department to make copies
of
Tek copy righted materials that Tek no longer makes available for sale. I
plan to use this permission but it is too early to talk about it at this
time. Stay tuned . . .

Stan
w7ni@easystreet.com


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Re: Washing Oscilloscopes

Stan or Patricia Griffiths <w7ni@...>
 

dhuster@pb.k12.mo.us wrote:l

I won't let you

disagree with me. I'll ease my stance over to the fact that water
supplies aren't the best they can be, some places are better or worse
than others, and you can get trace elements and compounds in there
that can skew circuit parameters. I'll also agree that cavalier
washing of state-of-the-art electronics using 1976-era techniques can
be foolish.

Still, I don't ever remember old Ed Lundsford, our 500-series
technician, ever having to replace a LV or HV transformer after a
washing. Now, if you ever wanted to see a ripe candidate for the
wash, all you had to do was get in a scope that had been sitting on
the machine shop floor 24/7 at Halliburton Industries. Oil would be
dripping out of the case.

Dean
I sure agree with taking it very carefully with the newer scopes with regard
to the wash process. I have very little experience with anything newer than
about 1970.

I, too, have seen a few scopes that were used in machine shops with oil
dripping out of them. Talk about filthy . . . WOW ! !

I don't ever remember losing an actual high voltage transformer to the wash
process . . . only power transformers and then only due to breakdown of the
CRT filament winding to ground.

So, I guess we agree . . . again . . . still . . .

By the way, the readers of this list will be interested to know that I have
obtained WRITTEN PERMISSION from the Tek Legal Department to make copies of
Tek copy righted materials that Tek no longer makes available for sale. I
plan to use this permission but it is too early to talk about it at this
time. Stay tuned . . .

Stan
w7ni@easystreet.com


Re: Washing Oscilloscopes

Stan or Patricia Griffiths <w7ni@...>
 

Hi Miroslav,

My comments are inserted below:

Miroslav Pokorni wrote:

Stan,

On the other note, I have a question on washing. In your book you described
a 'low cost' wash set up and mention spray gun with siphon suction for
water. I looked around and it was pretty hard to locate such a beast. The
one that I found at Grainger costs over $50 and requires 4 CFM of air, what
translates to another $200 for a new compressor; one that I have is only 2
CFM. Shelling out $250 is pretty steep price for washing a single PS503A.
Can you be more specific about spray gun that you have: make, model, CFM, etc.
Well, expensive or cheap is a relative term, I guess. The original washing
facilities that I was familiar with were those at Tektronix. They had a wash
booth lined with galvanized sheet met with a ventilated hood and it was plumed
with hot and cold running water and a drain system. There was also a "lazy
susan" to set the scope on so it could be easily turned with every side facing
the person doing the washing. This set up HAD to cost at least several thousand
dollars. And then there was the drying oven. Tek bought some large ovens that
would hold maybe 6 scopes at one time. There were around $4000, as I recall
it. They consumed a lot of power and had to have special high current circuits
to supply it. The air compressor seemed to be the low cost part of this whole
setup. So that is what the "high end" of washing facilities looked like.

I do my washing outside on good days so I have eleminated the wash booth,
ventilation system, and lazy susan totally. I just set up two saw horses in my
yard and put a piece of plywood on them as a table top. I prefer plywood to the
steel lazy susan anyway as it is not as hard on the painted parts of the scope.
I also cut way down on the cost of the oven by usine an old refridgerator as an
insulated box that I heat with hot plates purchased from the local Goodwill
Store for about $2 each. These are plugged into a plug strip mounted in the
refridge box and controlled by a hot water heater thermostat which can be set in
the 130 degree heat range. The hot water thermostat was the most expensive part
since I had to buy it new for about $20. I already had a double squirrel cage
blower that I mounted on the outside of the refridge box to blow air across the
hot plates sitting on the bottom of the inside of the refridge box. This meant
I had to drill a couple of 2 inch or so holes near the bottom by the hot plates
to let the blower push fresh air into the box. I also cut another hole in the
top, about 2", to let the moist air out. I also acquired a cooking thermometer
(the kind you can stick into the center of a turkey) at a thrift store for a
buck or two. I drilled another hole and poked the thermometer through the
refridge wall so I could read it from the outside and the sense element was on
the inside. You really don't want to let the temperature in the box get higher
than about 130 degrees F or you might melt some plastic parts (like a delay line
. . . I know this from a sad, personal experience). Mostly, you want to put a
sheet of metal between the radiating hot plates and the bottom of the scope in
the drying oven to keep them from radiating heat directly into the scope. Lots
of air from the blower will keep the temperature pretty even in the box.

I took a look at my spray gun and it is a DeVilbiss Type DGD. It has a nozzle
on a piece of tubing about 12" long so it is easy to reach way inside of the
scope to get at the hard to reach places. I can't remember what I paid for the
spray gun but I did buy it new . . . probably about $50. I had to buy a
compressor, too, but I really needed one in my shop anyway. The spray gun uses
a siphon hose to draw the detergent/water mix into the spray gun. It helps to
elevate the bucket of detergent/water to near the level of the scope you are
washing since it siphons so much easier when you do that. I use about 100
pounds of air which I think is quite a lot more than Dean said he used. I find
that lots of high pressure air really helps to get the grime off of the ceramic
strips in the HV area. One caution . . . some sampling instruments have diodes
mounted in clips and you can blow them right out of their mountings, never to
find them again, and you might not find replacements, either . . .

So, counting compresser, spray gun, oven, and all, I think I have maybe $300
dollars in my wash system. That's CHEAP when compared to the $10,000 system Tek
used.

One advantage that local Tek scope collectors have in this area is that I have
often washed instruments for them and dried them in my oven. If there was any
way you could pool resources with other people who want to wash instruments,
this whole process might be more affordable . . .

As an alternate solution, what do you think of using straight water jet. I
was thinking of using air to pressurize a 1 gallon polyethylene spray tank
(they can take 35 to 45 PSI) and to change nozzle to a full cone, i.e. a
simple cylindrical opening. That would be a true Low Pressure Low Volume
cleaning, but might do the job.
You could certainly try it but after you spray and rinse the instrument, it is a
good idea to use high pressure air to blow most of the water out of it before
you put it in the oven. Even water with no ions in it can cause water spots and
blowing the water out of the instrument gets rid of most of them.

As for detergent, you said that Simple Green was your choice. In these days
there is a Crystal Simple Green and Simple Green. The Crystal is supposed to
be no odor, no residue. What would be your choice?
I use regular Simple Green in liquid form now and I don't notice any oder from
it. I mix it about 10:1 with water for spraying and use some non-diluted with
plastic scrub brushes and tooth brushes in the really dirty areas, like front
panel knobs and around the fan motor and high voltage. When I was first exposed
to washing scopes at Tek, we were using Kelite Spray White in granular form. We
would dissolve it in water, but I don't remeber the concentration . . .
Occasionally, grains of undisolved detergent would clog the spray gun. Later,
we used another liquid detergent called N-L Concentrate. All of these
detergents seemed to get the scopes clean and do not seem to cause any
electrical problems with the electronics. At first, when we would lose a power
transformer, we thought it was due to spraying detergent into the transformer,
and maybe it was, but now it seems more like ion-contaminated water was the
problem all along. One of the problems with using powdered detergent is that
you have to stir it a lot the get it dissolved and then it is hard to make a
really concentrated solution for the extra dirty areas of the scope. The liquid
detergents seem so much easier to me . . .

The grease that you used to re-lubricate switches with, name escapes me now
and your book is not here. Tell me where did you buy it.
Well, I use "Lubriplate" to lubricate switch detent balls and I don't really
know its composition. It is a white grease but there must be a lot of good
types out there to use for lubing the detent balls. If I want to lubricate the
swith wafers and contacts, I use Caig DeOxit in the liquid form and apply a very
small amount with a cotton swab. I have used WD-40 in the past and it seem to
clean up noisey switches, pots, and tube sockets but the problems come back
soon. I have been told that the "good stuff" in WD-40 evaporates in a couple of
weeks or so and this may be why it does not seem to last. I understand that
DeOxit is available in a spray can, too, and this could be very handy in some
places that you can't reach with a swab (like 453 vertical attenuator switches).


Regards

Miroslav Pokorni
I hope this helps a little, Miroslav. Please keep us informed about your
progress in further refinements of the scope washing process.

Stan
w7i@easystreet.com


Re: white relays

david@...
 

Hello David,
I saw your reference to these low capacitance relays, I have a 7A11 with
some of these, which are faulty, where can I get some, any leads ?.
The only source I know of is Deane Kidd (dektyr@teleport.com). The last
time I asked him, he was selling them for USD 25 new, or USD 10 used :-(
You can see that you might be better off taking them out of junked
7A11/7A12/7A13 plugins.

Also, if you are extremely careful (and lucky), you can cut open the
plastic with a hot knife, and possibly get them unstuck with contact
cleaner.


Re: white relays

William de Bruyn <liam@...>
 

Hello David,
I saw your reference to these low capacitance relays, I have a 7A11 with
some of these, which are faulty, where can I get some, any leads ?.

Regards
William de Bruyn


Re: 7503

dhuster@...
 

Miroslav,

I was always under the impression that the whole thing was caused by
the Edison effect, metal particles being attracted by a surface
external to the lamp, charged positive with respect to one side of
the filament, the metal particles finally darkening the inside of the
envelope killing light output. Eventually, enough metal erodes from
the filament that a low-wattage capability section of the filament
develops that can't handle the inrush current at turn-on, gets a
little too hot and melts the filament into an open.

Steve Schmelzer, a former Tek employee with whom I served in the U.S.
Navy, used to quip that a lamp operates not put emitting light, but
bu sucking up dark. They fail when they've sucked up all the dark
that they can hold, obviously proven by the dark insides of the
lamp. And such is how many theories are born.

Dean


Re: 7503

John Rehwinkel <spam@...>
 

At 1:51 PM -0700 2001/10/17, Miroslav Pokorni wrote:
powered and there is an effect called 'filament notching' that makes
a notch in tungsten filament and shortens life. I do not know how
that notching comes about, I would have to look it up.
As I recall, a notch starts out due to filament evaporation (in
a random spot, or one already slightly thinner than average).
This thinning creates a hot-spot, which only accelerates evaporation
from that spot. I think it can happen with AC too. It's what
halogen lamps try to reduce, by depositing the evaporated tungsten back
on the filament. I think.
Actually, that's the mechanism that takes over once the notches
appear (creating hot spots). The notches themselves are in fact
caused by tungsten atoms migrating in the direction of current
flow along the fault lines between grains. In AC use, this only
tends to occur where there's a thermal gradient (i.e. the ends
of the filament). In DC filaments, this occurs along the entire
unit.

A web search on "filament notching" yields lots of hits,
including these two (both have illustrations). The second
one even mentions that filaments drawing less than 40mA
(i.e. thin filaments on low candlepower lamps) at 1800-2250K
(typical long life lamp temperatures) are particularly
susceptible.

http://www.htl.co.jp/pro/kogata/tokusei_e.html
http://www.lumex.com/tech_notes/mini_txt3.html

-- John Rehwinkel KG4L
spam@fgm.com


Re: 7503

Michael Dunn <mdunn@...>
 

At 1:51 PM -0700 2001/10/17, Miroslav Pokorni wrote:
powered and there is an effect called 'filament notching' that makes a notch
in tungsten filament and shortens life. I do not know how that notching
comes about, I would have to look it up.
As I recall, a notch starts out due to filament evaporation (in a random spot, or one already slightly thinner than average). This thinning creates a hot-spot, which only accelerates evaporation from that spot. I think it can happen with AC too. It's what halogen lamps try to reduce, by depositing the evaporated tungsten back on the filament. I think.

Michael


Re: 7503

Miroslav Pokorni <mpokorni@...>
 

Dean,

As you said, the measurement after burn in is mostly to equalize light
output. Additionally, if intensity sticks out of expected range that is an
indication of a manufacturing defect. All these lamps in 7000 Series are DC
powered and there is an effect called 'filament notching' that makes a notch
in tungsten filament and shortens life. I do not know how that notching
comes about, I would have to look it up.

I found out about 'filament notching' in a Chicago Miniature application
note, which I do not have here. In these days of Internet you would say go
to Chicago Miniature web site, but there are no application notes there, so
I would have to look it up when I get home.


Regards

Miroslav Pokorni

-----Original Message-----
From: dhuster@pb.k12.mo.us [mailto:dhuster@pb.k12.mo.us]
Sent: Wednesday, October 17, 2001 12:59 PM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: 7503

Miroslav,

I wasn't the white relay guy. But as far as test and
burn-in, it may
be that Tek wanted all the lamps to have the same light
output so
that those vertical and horizontal mode switches across the
front of
the 4-holers would be the same intensity. And I suppose
that they
did the burn-in figuring that most lamps, if having a
manufacturing
defect, will fail within the first hours of life.

Dean



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