Hey guys! Look at me with my newly acquired acronyms! ;-)
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On Thu, May 28, 2020 at 03:39 PM, <ciclista41@...> wrote:
Still great advice for later when I'm working on a DUT with a SMPS. :-)
On Thu, May 28, 2020 at 03:34 PM, <ciclista41@...> wrote:
Excellent advice, Eric!
Now I'm glad I just put that incandescent bulb in series when I turned it on
the first time. Not that I have a variac (yet).
Bruce
On Thu, May 28, 2020 at 12:53 PM, Eric wrote:
I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one
transistor
so far that has "kind of" failed that one took a 576 to find it, was out
of
a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and
can
be damaged. Slow up on a varic is ONLY good for linear power supplies.
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Still great advice for later when I'm working on a DUT with a SMPS. :-)
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On Thu, May 28, 2020 at 03:34 PM, <ciclista41@...> wrote:
Excellent advice, Eric!
Now I'm glad I just put that incandescent bulb in series when I turned it on
the first time. Not that I have a variac (yet).
Bruce
On Thu, May 28, 2020 at 12:53 PM, Eric wrote:
I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of
a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.
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Hi Eric,
Must they be removed from the circuit to get decent readings? If so, I'll do it. This thing seems to have been designed to make it easy to remove them once the large caps are removed.
Bruce
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On Thu, May 28, 2020 at 12:53 PM, Eric wrote:
I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.
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Excellent advice, Eric!
Now I'm glad I just put that incandescent bulb in series when I turned it on the first time. Not that I have a variac (yet).
Bruce
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On Thu, May 28, 2020 at 12:53 PM, Eric wrote:
I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.
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184 Time-Mark Generator lamp
Hi all,
I recently acquired a rather nice shape 184 for the princely sum of $70. After some good burn in and exercising the controls following by a few adjustments, it ticks along perfectly except for the HF oscillator (but that's beyond the scope of this topic) and the green power lamp (above the oven lamp, which is working), which is burned out. I was surprised to find the bulb is one assembly that plugs into the socket. I assume these are probably unobtainium, but would be interested in being contacted off list if someone has one they are willing to part with.
Thanks!
Sean
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One of the things being added to my workshop is a vacuum system that would be suitable to pump down a CRT, but I wouldn't entrust myself to a CRT as rare as the one in the 576 as a test candidate! I can live with the burned spot for now, but thanks for the offer.
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From what I've read...Tek took a systems approach with this series of 2400 scopes... so it's fair to consider a 2465B scope plus the Tek recommended P6137 as what Tek intended... when interpreting the Tek specs about them.
Taking that way of looking at it... the DUT is on one end of the system, and you are on the other... and so what you see is what you get.
I've a feeling that Tek enthusiasts might buy a Tek scope just based on the nominal bandwidth, and then look for probes with a matching nominal bandwidth.
Given just the above, and assuming too, that the front end, filter response, of a 2465B is Gaussian, then:
(1) BW(system) = 1 / sqrt[ 1/(probe bandwith ^2) + 1/(scope bandwidth ^2) ]
So from (1) it is easy to see... if the bandwidth of the scope and the probe match... the nominal bandwidth of the system is scaled by 1/sqrt(2)
Thus, for a 400 MHz nominal bandwidth... (1) gives a system bandwidth of approximately 282 MHz. (Check the calculation!)
For a 2465B... that's a "sweet spot" in the sense that reducing the nominal bandwidth of the probe is only going to reduce the system bandwidth... but given the high non-linearity of (1), its not a proportional reduction.
So consider using a probe with a nominal bandwidth of 100 MHz. Then (1) gives a system bandwidth of approximately 97 MHz. That is pretty close to the nominal bandwidth of the probe.
The takeaway from (1) is that just considering bandwidth specs... if you are working on 10 MHz timebase, with a 2465,B... say just for the features that Tek offers.. then using a P6105 probe is probably okay. (I say probably...because Tek specs a P6105 for 15 pf, on the lower end of the compensation... and Tek specs the input of some? 2465Bs at 15 pF + - 2 pF.)
Best regards and wishes.
Roy
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Raymond,
Thanks for verifying. I thought that I knew these scopes pretty well. But I have been wrong before and it would not have been the first time that I stuck my foot in my mouth.
I have a TDS360 and TDS460A and those both use the SMPS design, but totally unrelated to the 4xx Series.
--
Michael Lynch
Dardanelle, Arkansas
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On Thu, May 28, 2020 at 10:36 PM, Michael W. Lynch wrote:
I am pretty certain that the 455/465/475 use a linear power supply.
That is correct. Raymond
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However do NOT bring up a 400 series scope slowly on a variac. The 400 series have switching power supplies they are not the linear supplies They can over current when the line voltage drops to low to regulate and can be damaged. >Slow up on a varic is ONLY good for linear power supplies. Eric, I am pretty certain that the 455/465/475 use a linear power supply. That is the purpose of the big heavy transformer in the back of the scope. If it was a SMPS then there would be no need for that heavy beast. -- Michael Lynch Dardanelle, Arkansas
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On Thu, May 28, 2020 at 08:36 PM, Jim Ford wrote:
I was able to adjust the probe to get a nice flat response when connected to
the calibrator on the 54504A. Fortunately it also looked flat with the
calibrator on my Tek 7904.
Hi Jim, The artifacts that I was referring to don't show up on standard 'scope calibrators. Those only allow you to adjust "LF" behavior with a 1 kHz square wave (flat top). I meant fast-edge behavior, like that visible with <=1 ns steps in the first few ns or in the edge itself. That's where the differences are. You won't just see a flat or single-curved top but all kinds of ripples, resonance-like behavior etc. I know about only one "classic" Tek 'scope that offers that kind of fast step: the 485 in addition to a nice 1 kHz square wave. It allows LF adjustment *and* HF adjustment. The latter is done with separate adjustment regulators in the compensation box of the probe, underneath the plastic cover. *And* you need a well-matched input to the probe, like a probe-shaft-to-BNC adapter The calibrator's edges in the 7904 are no faster than 250ns so they are useless for showing the differences between e.g. the P6139A and P6137, much less perform the HF adjustment I was referring to.
And I'd check the input capacitance of the scope (7 pF in the case of the 54504A) versus the output capacitance of the probe (8 pF in the case of the P6139A), and
if they are close, you will probably get good results when you connect the probe to the calibrator and adjust it for flatness.
That's not correct: 8 pF is the nominal *input* capacitance of the P6139A and they don't have to be nor will be equal. Otherwise, you wouldn't be able to adjust an 8pF or 1.5 pF FET input capacitance probe to several different 'scopes, like the 2465B with its 15pF nominal input capacitance or a 7A26 with 22pF nominal. It's all about RC times, probe input, cable, probe output, 'scope input. The publications I referred to show it all. Nothing to worry about for general 'scoping in the sub-100MHz domain though. Who said that 100 MHz actually is DC? Raymond
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I would test the rectifiers the silicon is usually pretty resilient and normally grossly fails "open or short". I have only run in to one transistor so far that has "kind of" failed that one took a 576 to find it, was out of a fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac. The 400 series have switching power supplies they are not the linear supplies They can over current when the line voltage drops to low to regulate and can be damaged. Slow up on a varic is ONLY good for linear power supplies.
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Bruce,
Another critical peace of advice. Before you tare something down take a TON of picture from ALL angles. This will aid you in reassembly. A digital camera in the lab can save you hours in a schematic when you have a 50/50 shot of getting a power plug backwards and popping something. Also however many picture you THINK you need take double invariably there will be an angle you are missing that you need.
Eric
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Martin,
??? Unfortunatly I can answer that. I have the tube in question it is weak. It is doing a double ramp but this one is slightly weak. I have a second tube as well that is VERY weak. I have not looked in to rejuvination of these or rebuild yet let me know if you are interested They came to me at cost of shipping and I am more then happy to pass them on for cost of shipping.
Eric
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On 5/28/2020 5:35 AM, Martin Whybrow wrote: Ryan, has that CRT been taken? If not, I would be interested, does the screen appear burned? My 576 works, but has a completely dead spot where the intensity was left too high with a static spot displayed.
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I agree. I recently grabbed a P6139A out of Raytheon Technologies (RTX, my day job) e-waste bin and found that it works well with my 400 MHz HP 54504A scope (also an RTX rescue). I was able to adjust the probe to get a nice flat response when connected to the calibrator on the 54504A. Fortunately it also looked flat with the calibrator on my Tek 7904.
So, yes, for most purposes a properly adjusted 500 MHz probe will work with a 400 MHz scope. If you're testing pulses up near the limit (handy rule of thumb is pulse rise/fall time is 0.35/3 dB bandwidth), say 0.9 ns (about 400 MHz 3 dB BW), then no, you won't get an accurate picture unless you use the probe specifically designed for the scope. Also handy to remember 1 ns rise or fall time is equivalent to 350 MHz 3 dB BW, and 1 GHz BW is equivalent to 0.35 ns rise or fall time.
And I'd check the input capacitance of the scope (7 pF in the case of the 54504A) versus the output capacitance of the probe (8 pF in the case of the P6139A), and if they are close, you will probably get good results when you connect the probe to the calibrator and adjust it for flatness. Sometimes you can even find the range of capacitance of the probe. The HP 10430A probes I have with the 54504A scope say "1 Megohm||6.5 pF for 1 Megohm||6-9 pF inputs" on them. Also check to see what probe(s) go with what Tek scopes.
There's more, but it's probably covered in those references Raymond mentioned.
Good luck!
Jim Ford
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------ Original Message ------ From: "Raymond Domp Frank" <hewpatek@...> To: [email protected]Sent: 5/28/2020 4:49:56 AM Subject: Re: [TekScopes] probe. On Thu, May 28, 2020 at 07:40 AM, James Theonas wrote:
Is this probe a good match for my scope?
It would be insofar as bandwidth is concerned. The transient response however is not matched to the input characteristics of the 2465B. It'll work but signal fidelity will not be optimal, resulting in visible step response artifacts. For the 2465B, Tek recommended the P6137. With the right tools and equipment, you could optimize the behavior of the probe with its high-frequency adjustments.
Raymond
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James,
Maybe my earlier response was a bit terse and therefore limited.
The general answer to your question "Is this probe a good match for my scope?" should be "no". Chuck's answer and mine show you why:
You will not in practice achieve the "promised" 400 MHz bandwidth with that combination. But, neither will you with the Tek-specified P6137. That does not mean there's no observable difference between the two under any circumstances. Under specific test circumstances the difference is clear.
If you purchase a P6139A with the intention to observe and measure over the full bandwidth (bw) of the 2465B 'scope, you'll be disappointed. In fact, *no* high-impedance passive probe will do, as Chuck explained. One might add that the source impedance used for specifying scope bw is 25 (!) Ohm. Not many real-life signal sources fit that requirement!
At frequencies below 100 MHz or edge speeds slower than ca. 15ns the P6139A will provide acceptable fidelity. Most people use their 'scopes in that range and it makes no real difference if you use a P6139A, P6139B or a P6137.
Remember that for looking at edges, it's not the frequency but the edge speed that determines the speed requirements. For faster speeds either a fast FET probe or a Lo-Z probe with 50, 500 or 500 Ohm is a better choice. Get a copy of Tek's "ABC of Probes" or Doug Ford's "The Secret World of Oscilloscope Probes" and read all about it.
As said, for things like audio, Arduino projects, shortwave Ham and the like, a P6139A or almost any other "HF" quality passive probe will make you happy. That's where Chuck's P6105, 6, 7 choice comes in. They can often be had at low prices. If you get one of those, try and get a low-inductance ground clip/wire, unless you only do audio. The standard ground wire (4 - 6 inches) produces huge ringing, even at frequencies below 100 MHz. And choose an attenuation of 1:10, *not* 1:1. If you want to know why, read the publications mentioned above.
For anything faster, go Lo-Z (cheap/very cheap (DIY possible)) or (Hi-Z) FET.
Raymond
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On 2020-05-27 11:20 PM, Mlynch001 wrote: ... Many Tantalum caps do not have a voltage designator band. This one is supposed to be 50V, according to the parts list. That Voltage Value can usually be derived indirectly from the known operating voltage of the circuit. In this case, common sense tells us this cannot be a 16V cap, since it is operating in a circuit using a higher voltage than 16V. You would want to replace this with one of at least the same or greater voltage rating.
If you're going to the trouble of ordering new ones and replacing, I believe it's also now understood to be good practice to de-rate tantalums by *at least* 2 x the operating voltage. (In these lists I've heard a lot of cases where the originals were barely de-rated and thereby producing unnecessary failures -- even in Tek gear, perhaps moreso the newer SMT.) --Toby
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Tektronix tweaked the probes meant for the 2465B to match
the response of the inputs on the 2465B, so for specified
performance, only a p6137 will do.
But, likely you will never notice the difference.
The 10M, probe tip, frequency response of these scopes was
simply bragging rights for tektronix.
The parallel capacitive reactance at the probe tip swamps
the probe's 10M resistance long before you get to 400MHz.
It even swamps most circuits where you might think you would
like to make a measurement using a 10M probe...
Amuse your date, calculate Xc for the probe at 400MHz.
P6135,6,7 probes are pretty easily damaged. Often it is
better to get a much slower P6105,6,7 100MHz probe, and
enjoy its near indestructibility.
It is unlikely you will ever be bothered by its frequency
response.
-Chuck Harris
James Theonas via groups.io wrote:
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A quick question for the group. I have a 2465b and have found a p6139a locally in good condition. Is this probe a good match for my scope?
Dimitris Theonas
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Hi Bruce,
Okay - I was thinking the 475's caps were the same as the 465 but perhaps not.
It's a custom board I designed and had manufactured. BTW, if you notice, the board shown has a trace that had to be removed for that version of the board (I made a mistake...). I had another batch made where that wasn't necessary.
Thanks,
Barry - N4BUQ
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----- Original Message ----- From: "ciclista41 via groups.io" <ciclista41@...>
To: [email protected]
Sent: Thursday, May 28, 2020 2:22:48 AM
Subject: Re: [TekScopes] 475 questions
Hi Barry,
That certainly looks like a neat way to handle it! I've already order the
disc-shaped ones for this board. As far as I know, there isn't a similar
set-up available for the 475, but I like the single board with stand-offs.
My 475 has six large caps there, rather than five, although I read
somewhere that two of these are in parallel, so can be replaced with a
single cap. Was that solution a custom job, or purchased ready made?
Bruce
On Wed, May 27, 2020 at 08:03 AM, n4buq wrote:
I have hesitated to mention this as a possible approach to the filter caps
in
the 475 because:
1. I don't know for sure whether the layouts between the 465 and 475 are
identical
2. The design is, well, a bit kludgy (if I do say so myself)
However, I thought I'd pass it along.
Pictured in this album is an implementation of a separate circuit board
that
provides that ability to use common snap-in caps as replacements. My
intent
for this was to make it possible to replace those caps again (should it
every
become necessary) without further desoldering/soldering on the main board.
/g/TekScopes/album?id=64929
There are small disc adapters that do somewhat the same thing (I have
some);
however, if a future cap replacement becomes necessary, I'm not sure it is
possible to do that without removing the disc which, of course, involves
solder work on the main board.
Maybe one day I'll afford a snazzy desoldering tool which would probably
(certainly?) make that part much easier for me but, for those large can
connections, it's not fun with a 25-year-old Radio Shack solder sucker.
The
can, itself, is a rather large heat sink/spreader which further complicates
that process.
Anyway, FYI.
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "VK1GVC" <vk1gvc@...>
To: [email protected]
Sent: Wednesday, May 27, 2020 9:40:45 AM
Subject: Re: [TekScopes] 475 questions
Bruce, I treat tantalums like I treat people - assume they have good
intentions unless I learn otherwise.? If you remove lots of them without
reasonable suspicion then you'll probably do more damage than good as
Eric has warned.? As tantalums usually fail to a short circuit, a
failed/shorted tantalum will pull down the voltage at that point to
close to zero and this will/should be straighforward to find - later.
At this stage, if I haven't missed any key points, you've found 2
sick/dead capacitors in the +50V supply which MAY be the cause of all
the wrong voltages you've measured in the low voltage power supply
section.? So replace those caps first, then adjust all of the LV power
supply to meet calibrations specs and see what happens.? You might have
a working scope if luck is very much with you, or you might be one step
on a long journey towards that goal.
And when you replace the tantalum which lost a leg, make sure you
install the new one with the right polarity.? Tantalums don't like
reverse voltage and they can get hot, emit smoke and explode.? I've seen
it happen when a workmate powered up some newly assembled eqpt for the
first time and heard a hissing sound so he bent down for a better look.
A cylindrical metal tube type tantalum then exploded and flew off the
PCB, burning itself onto the side of his neck. Very painful ... and the
language was terrible.? And very lucky he didn't get hit in an eye.
BTW here's a different type of tantalum which I don't think has been
mentioned yet - see the colourful little blob in the lower left of the
picture at this link:
/g/TekScopes/photo/12901/22?p=Name,,475,20,1,0,0
It has a black top, brown middle and green bottom ... the colours are a
derivative of the resistor colour code and I think there's a spot on one
side too.? Much better dressed than a plain boring tantalum!
Graham
On 27/05/2020 3:28 pm, ciclista41 via groups.io wrote:
Graham,
Well, my scope is peppered with the kind in the photo. Maybe they
re-spec'ed the caps later in production, or maybe the US Army bought
enough in their contract with Tek that they were able to spec what they
wanted. Mine is from November of 1982, if the date code on the AC
power
cord box inside the case just above the transformer is original.
I went ahead and pulled the two tantalums out of the circuit to measure
them. I broke a lead off the first one, pulling too hard. Because I
only
have access from the top of this A7 board unless I remove it, which I
don't want to do, my solder sucker wasn't able to slide over the
clipped
end of the leads, and I had to just use a sharp tip on my iron. Did
much
better on the second one, which came out easily by that second method.
I
then used the sucker to remove the remaining solder from the holes in
the
board for when I replace the broken one.
Yes, you were right to question my belief that they were bad. Out of
circuit, they both tested well within the green on my ESR tester. So
much
for being able to reliably test capacitors in circuit with that thing.
They weren't even close to being in spec when tested with it in
circuit.
I was thinking that these dipped tantalums were generally bad in boards
this old based on numerous threads in this forum and others saying how
often these were bad. Some said they routinely replace them all when
they
see them in a scope of this era. I have tested dozens on this board and
only found about a handful that this tester considered bad. So,
considering that these two were among the worst that I tested in
circuit,
I decided to pull them, as they'd be less easily accessible later when
the
A8 board is back in place.
So this makes me question whether the tantalums in this board are among the
infamous ones. I hope not, obviously. Your statement that my photo
showed what looked like a very '80's tantalum made me think maybe the
infamous ones are some earlier 60's or 70's version. How can I know,
other than pulling them all? At this point, I don't see the point of
pulling any of them unless they show up as faulty later, when there is
a
trace on the scope and I can run it through its paces and make sure
it's
working as it should.
Speaking of working as it should, Tektronics calls for several
specialized
calibration tools in the manual. If the scope is running well, with no
serious issues other than calibration, can it be calibrated without
resorting to the purchase of such tools? I briefly noted some shops
wanting a couple of hundred dollars to calibrate a scope. Definitely
don't want to do that! If I thought I had to have someone else
calibrate
it, I probably wouldn't have taken on the project and just invested in
a
new digital scope.
Bruce
On Tue, May 26, 2020 at 09:09 PM, VK1GVC wrote:
Bruce, the link to the pics on TekScopes worked for me and that
capacitor looks very 1980's tantalum as Michael confirmed in a later
475
manual and the Tek Common Parts manual.? Ceramics of that era were
commonly flat circular disks, very different from what you have.
Roger re testing in place - very problematic.? Best to remove them to
eliminate any ambiguity and as you have reported success in
desoldering
then that's the best option while you have access.? BTW I'm curious to
know why you *believe* that they are faulty - mere suspicion based on
type and age, or something else?
You quoted your post of 22 May to Harvey a few minutes ago in which
you
sought advice about what can and cannot be substituted when replacing
1982 components in 2020.? Has that qn been answered to your
satisfaction
or is it still a live issue?? The short answer is: it depends.? The
long
answer really has to address a specific component in a specific
application.? But the laws of physics haven't changed a lot in the
last
40 years so there is almost certainly something out there which can be
bought/found/made/adapted or cajoled to do the job.? If you need a
1amp
400V rectifier diode then a IN4004 of the 70's or 80's is just the
same
as one from the factory today.? If you need a very specific high-spec
module made for or by Tek for a very challenging application 40 years
ago and now out of production ... oh dear, you've got a problem.
Fortunately we now have TekScopes, some wikis, eBay and of course the
WWW.
Graham
On 27/05/2020 1:24 pm, ciclista41 via groups.io wrote:
Hi Graham,
I posted a photo of the C1091 tantalum, along with the plaque stuck
to
the back of my scope here:
/g/TekScopes/album?id=247625&p=Created,,,20,2,0,0
Bruce
--
This email has been checked for viruses by Avast antivirus software.
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Re: Encouraging beginners: What are we accomplishing?
Many enthusiastic youngsters had comparable experiences with instrument companies in the 1960s. General Electric and to a lesser degree RCA were also very kind to young hams and experimenters. I spent my youth in a place where one huge chemical plant dominated the local industries. They had an extensive outreach to youngsters showing interest in science and especially technology, it paid off for them by providing an abundance of techie kids applying for employment after graduation. This was the company that invented super glue, at the time it was still under patent and only available from them. Their recruiters always came prepared with lots of it that didn't quite measure up but was still very usable. An occasional Tektronix, General Radio, or Hewlett Packard manual would also be in their bag. None of us with "pump gas-cut grass-throw papers" money could afford anything Tektronix unless we were exceptionally lucky and it for some reason showed up at the local scrapyard that took in from many regional industries. While some of us had driver's licenses, most of us got there on bicycles or walked. One testament to the quality of equipment was how well it survived a few miles in a bicycle trailer or cart.
Bruce Gentry, KA2IVY
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On 5/27/20 10:36 PM, stevenhorii wrote: My experience with Tektronix began far before I had a Tek scope. I was
about 11 years old and saw advertisements in Scientific American for
Tektronix oscilloscopes. I wanted a catalog to learn more about them. I
wrote a letter to Tektronix (I believe it was to the HQ in Beaverton)
asking for a catalog. Whoever received it must have figured out I was a kid
- no company name or address and clearly a home address. Best regards and wishes.
Roy
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Michael W. Lynch
Raymond Domp Frank