Date   

Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

On Tue, Dec 8, 2020 at 01:16 AM, Dave Peterson wrote:


I'm sure I could adjust my scopes as well as, if not better, than a dedicated
shop. But I know the difference is that I don't have certified standards to
validate against. But then my balancing thought is what you're saying about
0.1% - how many significant digits can one achieve with these things. Trying
to adjust a 465 pot to less that 1% is just not possible. Doesn't stop me from
trying. Wink. But if I have two or three instruments agreeing to 1% I have
good confidence that my adjustments are valid. But that's not really what
"calibrated" means.

Again, the issue circles back to what one is trying to sell. If I sold as
"calibrated" I wouldn't do that without: A) charging for it, and B) providing
the paperwork proving it. I like the term "performance verified". Or otherwise
functionally and performance verified or validated. I'll have to investigate
what eBay calls "Refurbished". Then again I'm probably holding myself to a
standard that other sellers may not. I gotta be me.

I've got a ways to go before I'll feel comfortable reselling a scope as
refurbished and verified. I also don't see myself selling one until I am
comfortable saying that. If I wasn't comfortable selling it as validated I'd
have to sell it as parts. Which I'm also not thrilled with. I don't see a
market for selling a "calibrated" 465 vintage scope. I'd leave that to the
buyer. If they need that, then it's part of their operating expense anyway.
Hi Dave,
I've considered responding re. calibration for a while but decided to wait what others would say - call me lazy.
So far, I haven't seen mentioned what I wanted to say:

In a strict sense, "calibration" means verifying against a standard, nothing more. For electronic instruments, the standard would be the specification of the instrument to be calibrated (DUT), *not* the specification of the instrument one is using to verify the DUT with.

A DUT is considered "in spec" or "calibrated" if it performs within its published specifications (all of them). IOW, if the published spec for vertical sensitivity of a 'scope is +/- 2% and it performs within +/- 1.5%, it is *within spec* in that respect (or parameter, or feature, whatever you like to call it). Since there are only two possibilities: *within spec* or *not* within spec, if it performs within say +/- 0.01%, it's not "more within spec" and in a sense, not even "better calibrated". It's just more precise.

While (or after, whatever you call) restoring, many hobbyists tend to start adjusting things like the low-voltage power supplies, because they have a pretty good DVM - but nothing else.
It's perfectly possible that the instrument was within spec ("calibrated") before that but after adjusting, no longer is, and they have no way to check or adjust because they'd need different instruments.

Many calibration labs distinguish between "calibrating" and "adjusting", with very different pricing. For many people (and in normal speak) calibrating means the same as adjusting. Strictly speaking this isn't so, as I explained above. You need to be aware of that.
It would seem to make sense to try and adjust close to perfect but that's not a requirement to be "in calibration".

Naturally, adjusting as much as possible precisely in the middle (aiming at +/- 0%) seems to make sense to allow as much drift as possible until you lose calibration status but even that's *not* true in all cases. It may depend on temperature behavior or aging for instance. If e.g. a particular model quartz oscillator is known to age toward becoming slower, it may make sense to adjust it a bit higher than exactly +/- 0%.

As another example, it may make very little sense to adjust within say 0.1% where the spec says +/- 2%, because the parameter could drift outside of that within minutes to say .3% (because of temperature variations or so) but stay within calibration (= spec) for a year because the drift would only be say +/- 1% over a specified calibration interval.

BTW, I don't think it makes sense to calibrate or even adjust a healthy 465/475 twice a year, as was suggested, unless it lives in an unhealthy or very unstable environment, because it's not expected to drift out of spec within such a relatively short period. Checking (calibrating!) a restored instruments initially after a few months may make sense.

Note: The drift that is seen with many old components, like carbon composite resistors, far exceeds normal drift that the original calibration interval is based on.

Raymond


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

Dave Peterson
 

Jeff,
I bought a cheap function generator that I wouldn't take home to meet my parents. Much less brag about here.

However, it is a modern piece of technology that I think can outperform my old 465 well enough to tell it how to dance. Modern run of the mill digital electronics are running at several orders of magnitude higher frequencies than this old scope.

I'm currently using it to generate square waves to use in place of a time mark generator. From what I've seen so far from the calibration procedure, and I've done a little tweaking on my existing scope with an even more embarrassing source of square waves (a free function generator app on my cell phone), the primary purpose is to provide a time standard to adjust sweep timing and also geometry edges for rotation and "Geometry, R1442" vertical alignment with the graticule. So giving you clean square edges for aligning the X and Y axis of your trace. The 465 can just make out the vertical edges of around 10-20ns. Plenty good for 465 edges.

Other entries in the calibration procedure use the time mark generator to calibrate (check and adjust) the B-sweep. I'm not clear on the process yet. I'm sure there are others. What I've seen of time mark generator output look like pulses more than square waves. But the effect is the same - regular vertical edges. The cheap FG will do pulses too. Anything actually.

The point being, I think a decently competent square wave generator can suffice as a stand-in for the time mark generator. Standards for level and time are subject to suspicion. But again, my sneaking suspicion is that the cheap function generator is within the tolerances of what the 465 can measure. I continue to contemplate how to validate it's time and levels. But this is far better than nothing, for a lot less $$.

Calibrated? No. Tuned up? Hell yes!

Dave

On Monday, December 7, 2020, 04:39:39 PM PST, Jeff Dutky <jeff.dutky@gmail.com> wrote:

demianm_1 wrote:

for a scope a time mark generator and a leveled signal generator would cover most tasks
Yes, it's the leveled signal generator that seems like the most challenging thing to roll my own. I've read that the time mark generator can be substituted with a fast pulse generator (which I have) though I don't claim to understand how the time mark generator is used or how the pulse generator could stand in for it. At some point I will sit down, read the entire calibration process, and read the manuals for the relevant calibration equipment, just so I can make a somewhat more informed decision about this.

You can get a full set of 500 series plugins for calibrating a 475 on eBay for about $500, though there's no guarantee that they are complete or completely functional. I could pay for calibration for a couple scopes with that same money. I suppose I could buy the calibration equipment, do any repairs that appear necessary, and then pay to have THEM calibrated, and then I'd be set to do my own calibrations. I feel, however, that that would only be worthwhile if I were going to be doing this as something other than a hobby.

-- Jeff Dutky


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

As this is just a hobby (at the moment, aside from trying to decipher display control signals in an old laptop, I basically just play with different entertaining scope features), and the big thing that I can't currently do is generate signals of a high enough bandwidth to actually observe the rolloff on any of my scopes (not even the 2213 or 2215A). I'd really like to be able to see the 3 dB attenuation when we get up to the scopes designed bandwidth (or to verify that the scope isn't making it up that far, as with the 475A that still seems to need some work). I've seen RF signal generators quite cheap on eBay (like this https://www.ebay.com/itm/ADF4351-35M-4-4G-RF-Signal-Generator-PLL-Sweep-Frequency-Generator-Touch-Screen/124031802437?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225074%26meid%3Dcaeae24012624d05b51677726176b070%26pid%3D100005%26rk%3D2%26rkt%3D12%26mehot%3Dpf%26sd%3D254800360814%26itm%3D124031802437%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV3BBEV2b%26brand%3DUnbranded&_trksid=p2047675.c100005.m1851 or this https://www.ebay.com/itm/35MHz-4400MHz-RF-Signal-Generator-ADF4351-Module-Sweep-Frequency-Generator-PLL-W/353206533830?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225074%26meid%3D96ac4e171b0d42f4b9223f51e4069b14%26pid%3D100005%26rk%3D5%26rkt%3D12%26mehot%3Dpf%26sd%3D124031802437%26itm%3D353206533830%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV3BBEV2b%26brand%3DUnbranded&_trksid=p2047675.c100005.m1851) would one of these be at least able to exercise my 475/475A in an interesting way?

-- Jeff Dutky


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

demianm_1 wrote:

for a scope a time mark generator and a leveled signal generator would cover most tasks
Yes, it's the leveled signal generator that seems like the most challenging thing to roll my own. I've read that the time mark generator can be substituted with a fast pulse generator (which I have) though I don't claim to understand how the time mark generator is used or how the pulse generator could stand in for it. At some point I will sit down, read the entire calibration process, and read the manuals for the relevant calibration equipment, just so I can make a somewhat more informed decision about this.

You can get a full set of 500 series plugins for calibrating a 475 on eBay for about $500, though there's no guarantee that they are complete or completely functional. I could pay for calibration for a couple scopes with that same money. I suppose I could buy the calibration equipment, do any repairs that appear necessary, and then pay to have THEM calibrated, and then I'd be set to do my own calibrations. I feel, however, that that would only be worthwhile if I were going to be doing this as something other than a hobby.

-- Jeff Dutky


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

Dave Peterson
 

This thread is validating my suspicions. I was surprised to accidentally come across a cal service website offering calibration for a 465 while looking for what the waveform on TP1478 (or something like that) was supposed to look like. Part of the Z-axis compensation adjustment. As Jeff noted, they're available, for more $$ than I payed for the scope.

I'm sure I could adjust my scopes as well as, if not better, than a dedicated shop. But I know the difference is that I don't have certified standards to validate against. But then my balancing thought is what you're saying about 0.1% - how many significant digits can one achieve with these things. Trying to adjust a 465 pot to less that 1% is just not possible. Doesn't stop me from trying. Wink. But if I have two or three instruments agreeing to 1% I have good confidence that my adjustments are valid. But that's not really what "calibrated" means.

Again, the issue circles back to what one is trying to sell. If I sold as "calibrated" I wouldn't do that without: A) charging for it, and B) providing the paperwork proving it. I like the term "performance verified". Or otherwise functionally and performance verified or validated. I'll have to investigate what eBay calls "Refurbished". Then again I'm probably holding myself to a standard that other sellers may not. I gotta be me.

I've got a ways to go before I'll feel comfortable reselling a scope as refurbished and verified. I also don't see myself selling one until I am comfortable saying that. If I wasn't comfortable selling it as validated I'd have to sell it as parts. Which I'm also not thrilled with. I don't see a market for selling a "calibrated" 465 vintage scope. I'd leave that to the buyer. If they need that, then it's part of their operating expense anyway.

Thanks for your inputs. Enlightening, educational, and entertaining, as always.Dave

On Monday, December 7, 2020, 03:30:32 PM PST, demianm_1 via groups.io <demianm_1=yahoo.com@groups.io> wrote:

My experience with cal labs has not been encouraging. Mostly they want to run instruments through the automated cal procedure. Anything else will be expensive (labor). And its really whether the instrument is within tolerance (go/nogo). Its not adjusted to perfect.  If adjustment/repairs are needed the rate can be astonishing and keep in mind on these older instruments the repairs are not 10 minute fuse replacements. They are usually really difficult things to figure out.

However for a scope a time mark generator and a leveled signal generator would cover most tasks. CRTs are not .1% instruments so no need to get that involved. I picked up a Ballantine 6130 time mark generator and a Tek 191 leveled generator (to 100 MHz) pretty reasonably. With those you could say "performance verified" instead of "calibrated".


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

demianm_1
 

My experience with cal labs has not been encouraging. Mostly they want to run instruments through the automated cal procedure. Anything else will be expensive (labor). And its really whether the instrument is within tolerance (go/nogo). Its not adjusted to perfect. If adjustment/repairs are needed the rate can be astonishing and keep in mind on these older instruments the repairs are not 10 minute fuse replacements. They are usually really difficult things to figure out.

However for a scope a time mark generator and a leveled signal generator would cover most tasks. CRTs are not .1% instruments so no need to get that involved. I picked up a Ballantine 6130 time mark generator and a Tek 191 leveled generator (to 100 MHz) pretty reasonably. With those you could say "performance verified" instead of "calibrated".


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

Jim Ford
 

I, too, have had issues with cal shops.  One sent my Tek 453A scope back with low frequency rolloff in A.C. coupled mode much different on ch1 vs. ch2!  I had to tweak it back in myself.  Never went back there again.    Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Stephen Hanselman <kc4sw.io@kc4sw.com> Date: 12/7/20 2:55 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] SUCCESS! The "sick" 475A is now the "fixed" 475A! My two cents are Watch the lab like an eagle. We regularly get equipment from one of our customers who “has” to use a particular cal house. It comes in either BER or out of spec, we then go through the manual and perform the required adjustments, send it back to our customer who sends it back to the lab and who then puts a sticker on it.Moral, most of the so-called cal labs do the verification (or maybe less) then either sticker it or reject it.  They do not seem to know how to do the adjustments or anything else for that matter. Ask me how many things we’ve fixed for this customer with parts cost less than $10.00 on equipment returned BER.Regards, Stephen HanselmanDatagate Systems, LLC> On Dec 7, 2020, at 14:42, Jeff Dutky <jeff.dutky@gmail.com> wrote:> > Dave,> > I am not, in fact, familiar with "real" calibration, except in as much as I know that I can't easily do it with what I have to hand (I suspect that I might be able to rig something up, but the price of doing so would probably rival the prices for the three important calibration devices on eBay), and if I DID rig something up, I'm not sure I could rely on the calibrations that resulted.> > My father apparently sent his 2213 in for regular calibration through the late 80s. That calibration appears to have been annual, judging by the dates on the stickers. I'm not sure why he stopped, but his service business started to dry up about that time, so I can imagine several explanations. He never bothered to get the 475 calibrated after he got the 2213. Again, I'm not sure why, but the fact that he was using a 60 MHz scope as his "daily driver" suggests that the 475 was well in excess of his needs, so maybe strict calibration wasn't too important either?> > I haven't tried any significant calibration of anything, only small stuff that (hopefully) doesn't throw off the rest of the scope (e.g. adjusting the invert balance on channel #2, and recalibrating the V/div balance). I haven't touched the sweep timing calibration, for example, because I know that would require equipment that I just don't have.> > My impression (from this group and elsewhere) is that you can still get these things calibrated by professional shops around the country (the place I'm looking at is www.custom.cal.com which has locations in New Jersey, Florida, and Oregon), and that it's not absurdly expensive (but more expensive than the old scopes themselves). I'm not sure what, if any, the extra cost is for a traceable cert.> > I'm pondering the same thing you are pondering, if only because it would be a possible way to defray the cost of acquiring these parts scopes. Also, I only need so many parts scopes, and I'm well beyond that number right now. I also need only so many working scopes, and I am probably beyond that number as well. I'm not sure what obligations you are under if you sell a scope as "working" or "restored". If I were going to charge the kind of prices I still see for "working" 475a on eBay, I would want to include at least a front cover, pouch, probes, and operators manual, and the scope would have to be in pristine cosmetic condition (but that's just me and my ridiculous scruples).> > The number of working scopes I need is a complicated question: While the 475 and 475A are on the bench (as subjects) I need a scope that I can use to work on them, which should be a 100 MHz scope (the 2236). However, the 2236 is currently on the bench (as a subject) so I need a scope to work on that one as well (which is either my father's old 2213, or the 2215A). The 2213 could also be on the bench, but I've given up trying to diagnose its intermittent channel 1 flakiness, so the 2215 is the primary scope for the moment, and everybody else is either a patient or a donor.> > -- Jeff Dutky> > > > >


Re: Calibrating a PG506 w/o Sampling System

Jim Ford
 

Right, John.  I've used both a 54120A and Tek CSA803, although upwards of 25 years ago, and they are quite similar.  I do prefer Tek scopes, and in this case, the modularity of the Tek beats the HP, with its somewhat cumbersome external triggering and sampling boxes.  OTOH, one could bring the boxes close to the DUT and leave the much bulkier scope box on the bench or in a rack.  I suppose one could do the same with the much more lithe Tek sampling head(s) and (a) extender(s).  Tek for time domain, and HPAK for frequency domain!   JimSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: "John Gord via groups.io" <johngord=verizon.net@groups.io> Date: 12/7/20 2:56 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Calibrating a PG506 w/o Sampling System Jim,The HP 54120A/54121A combination also gives very good sampling performance, and is sometimes easier to find at a good price.--John GordOn Mon, Dec  7, 2020 at 10:40 AM, Jim Ford wrote:>> Yeah, I believe that about the 7T11/7S11 pair, Chuck; I have a 7S12 and > a 7S11, with a couple of S-4 sampling heads and S-51 and S-53 for > triggering.  PITA to get them to display anything on the 7904!  At some > point, I will look for an 11800 series scope like the one I had at work > a few decades ago.  I don't remember any issues with triggering back > then.  And the SD-24 sampling head got top marks for pulse fidelity from > PicoSecond Pulse Labs (sold to Tek in 2014, IIRC) back then.  Just got > to run the purchase by the finance committee (my wife)!  She can't say > anything about the space it takes up; I have that covered with a 19-inch > rack next to my bench....> > Jim Ford> > ------ Original Message ------> From: "Chuck Harris" <cfharris@erols.com>> To: TekScopes@groups.io> Sent: 12/7/2020 9:32:49 AM> Subject: Re: [TekScopes] Calibrating a PG506 w/o Sampling System> > >I do the PG506 calibration on a tek 11801C.  It reveals> >all.> >> >But, using a 7104 will only make things worse, best not> >done. As Raymond says, a PG506 adjusted to a pretty> >waveform on a 7104 looks like something you could spear> >fish with on a 11801C.> >> >The 7T11/7S11 pair is supposed to be adequate with the> >proper sampling head, but I have never been able to get> >such a pair to work reliably.  It kind of drifts into> >a measurement, and drifts out.  I never found the problem> >to be worth investigating.  If someone wanted to, I am> >sure that my 7T11/7S11 pair could be had for a reasonable> >price... whatever that is these days.> >> >-Chuck Harris> >> >Raymond Domp Frank wrote:> >>  On Mon, Dec  7, 2020 at 05:17 PM, Jean-Paul wrote:> >>> >>>> >>>  From transient CAL of 2467B, I can say its a tricky and iterative> process, and> >>>  the correct gens and fixtures are essential.> >>>> >>>  You may get by with a 1 GHz digital scope but not the Chinese, HP, TEK or> >>>  Lecroy.> >>>> >>> >>  First of all: Unless the edge settings have been changed, it's probably> not necessary to adjust them because your work hasn't influenced them. I> certainly wouldn't touch them without the right equipment.> >>  OTOH, the transient response calibration of a PG506 is a very simple> adjustment, *if* you have the right equipment and perform the procedure> correctly: One capacitor for the positive edge (C1000) and one for the> negative edge (C940); optimize overshoot for both. That's it. Capacitor refs.> are for SM "Late Model": S/N B040000 up.> >>  However, since you're adjusting a rise/fall time <= 1 ns (that's spec, in> practice usually 700 ps or better), your 'scope (as a rule of thumb) needs to> have a rise time of at most 20% of that: 200 ps. That means a BW for a 'scope> with Gaussian behavior of at least 1750 MHz, about 1400 MHz with many digital> 'scopes.> >>  So, using a 1 GHz BW digital 'scope won't crack it: The edge may look fine> on it but probably will have serious overshoot, which you won't see on your> (too slow) 'scope.> >>  In practice, I'd consider 2.5 - 3 GHz to be the minimum BW required,> taking into account that actual rise/fall time of most units is about 700 ps.> >>> >>  Raymond> >>> >>> >>> >>> >>> >>> >> >> >> >> >> >


Re: Calibrating a PG506 w/o Sampling System

John Gord
 

Jim,
The HP 54120A/54121A combination also gives very good sampling performance, and is sometimes easier to find at a good price.
--John Gord

On Mon, Dec 7, 2020 at 10:40 AM, Jim Ford wrote:


Yeah, I believe that about the 7T11/7S11 pair, Chuck; I have a 7S12 and
a 7S11, with a couple of S-4 sampling heads and S-51 and S-53 for
triggering. PITA to get them to display anything on the 7904! At some
point, I will look for an 11800 series scope like the one I had at work
a few decades ago. I don't remember any issues with triggering back
then. And the SD-24 sampling head got top marks for pulse fidelity from
PicoSecond Pulse Labs (sold to Tek in 2014, IIRC) back then. Just got
to run the purchase by the finance committee (my wife)! She can't say
anything about the space it takes up; I have that covered with a 19-inch
rack next to my bench....

Jim Ford

------ Original Message ------
From: "Chuck Harris" <cfharris@erols.com>
To: TekScopes@groups.io
Sent: 12/7/2020 9:32:49 AM
Subject: Re: [TekScopes] Calibrating a PG506 w/o Sampling System

I do the PG506 calibration on a tek 11801C. It reveals
all.

But, using a 7104 will only make things worse, best not
done. As Raymond says, a PG506 adjusted to a pretty
waveform on a 7104 looks like something you could spear
fish with on a 11801C.

The 7T11/7S11 pair is supposed to be adequate with the
proper sampling head, but I have never been able to get
such a pair to work reliably. It kind of drifts into
a measurement, and drifts out. I never found the problem
to be worth investigating. If someone wanted to, I am
sure that my 7T11/7S11 pair could be had for a reasonable
price... whatever that is these days.

-Chuck Harris

Raymond Domp Frank wrote:
On Mon, Dec 7, 2020 at 05:17 PM, Jean-Paul wrote:


From transient CAL of 2467B, I can say its a tricky and iterative
process, and
the correct gens and fixtures are essential.

You may get by with a 1 GHz digital scope but not the Chinese, HP, TEK or
Lecroy.
First of all: Unless the edge settings have been changed, it's probably
not necessary to adjust them because your work hasn't influenced them. I
certainly wouldn't touch them without the right equipment.
OTOH, the transient response calibration of a PG506 is a very simple
adjustment, *if* you have the right equipment and perform the procedure
correctly: One capacitor for the positive edge (C1000) and one for the
negative edge (C940); optimize overshoot for both. That's it. Capacitor refs.
are for SM "Late Model": S/N B040000 up.
However, since you're adjusting a rise/fall time <= 1 ns (that's spec, in
practice usually 700 ps or better), your 'scope (as a rule of thumb) needs to
have a rise time of at most 20% of that: 200 ps. That means a BW for a 'scope
with Gaussian behavior of at least 1750 MHz, about 1400 MHz with many digital
'scopes.
So, using a 1 GHz BW digital 'scope won't crack it: The edge may look fine
on it but probably will have serious overshoot, which you won't see on your
(too slow) 'scope.
In practice, I'd consider 2.5 - 3 GHz to be the minimum BW required,
taking into account that actual rise/fall time of most units is about 700 ps.

Raymond









Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

Stephen Hanselman
 

My two cents are Watch the lab like an eagle. We regularly get equipment from one of our customers who “has” to use a particular cal house. It comes in either BER or out of spec, we then go through the manual and perform the required adjustments, send it back to our customer who sends it back to the lab and who then puts a sticker on it.

Moral, most of the so-called cal labs do the verification (or maybe less) then either sticker it or reject it. They do not seem to know how to do the adjustments or anything else for that matter. Ask me how many things we’ve fixed for this customer with parts cost less than $10.00 on equipment returned BER.

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Dec 7, 2020, at 14:42, Jeff Dutky <jeff.dutky@gmail.com> wrote:

Dave,

I am not, in fact, familiar with "real" calibration, except in as much as I know that I can't easily do it with what I have to hand (I suspect that I might be able to rig something up, but the price of doing so would probably rival the prices for the three important calibration devices on eBay), and if I DID rig something up, I'm not sure I could rely on the calibrations that resulted.

My father apparently sent his 2213 in for regular calibration through the late 80s. That calibration appears to have been annual, judging by the dates on the stickers. I'm not sure why he stopped, but his service business started to dry up about that time, so I can imagine several explanations. He never bothered to get the 475 calibrated after he got the 2213. Again, I'm not sure why, but the fact that he was using a 60 MHz scope as his "daily driver" suggests that the 475 was well in excess of his needs, so maybe strict calibration wasn't too important either?

I haven't tried any significant calibration of anything, only small stuff that (hopefully) doesn't throw off the rest of the scope (e.g. adjusting the invert balance on channel #2, and recalibrating the V/div balance). I haven't touched the sweep timing calibration, for example, because I know that would require equipment that I just don't have.

My impression (from this group and elsewhere) is that you can still get these things calibrated by professional shops around the country (the place I'm looking at is www.custom.cal.com which has locations in New Jersey, Florida, and Oregon), and that it's not absurdly expensive (but more expensive than the old scopes themselves). I'm not sure what, if any, the extra cost is for a traceable cert.

I'm pondering the same thing you are pondering, if only because it would be a possible way to defray the cost of acquiring these parts scopes. Also, I only need so many parts scopes, and I'm well beyond that number right now. I also need only so many working scopes, and I am probably beyond that number as well. I'm not sure what obligations you are under if you sell a scope as "working" or "restored". If I were going to charge the kind of prices I still see for "working" 475a on eBay, I would want to include at least a front cover, pouch, probes, and operators manual, and the scope would have to be in pristine cosmetic condition (but that's just me and my ridiculous scruples).

The number of working scopes I need is a complicated question: While the 475 and 475A are on the bench (as subjects) I need a scope that I can use to work on them, which should be a 100 MHz scope (the 2236). However, the 2236 is currently on the bench (as a subject) so I need a scope to work on that one as well (which is either my father's old 2213, or the 2215A). The 2213 could also be on the bench, but I've given up trying to diagnose its intermittent channel 1 flakiness, so the 2215 is the primary scope for the moment, and everybody else is either a patient or a donor.

-- Jeff Dutky





Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

Dave,

I am not, in fact, familiar with "real" calibration, except in as much as I know that I can't easily do it with what I have to hand (I suspect that I might be able to rig something up, but the price of doing so would probably rival the prices for the three important calibration devices on eBay), and if I DID rig something up, I'm not sure I could rely on the calibrations that resulted.

My father apparently sent his 2213 in for regular calibration through the late 80s. That calibration appears to have been annual, judging by the dates on the stickers. I'm not sure why he stopped, but his service business started to dry up about that time, so I can imagine several explanations. He never bothered to get the 475 calibrated after he got the 2213. Again, I'm not sure why, but the fact that he was using a 60 MHz scope as his "daily driver" suggests that the 475 was well in excess of his needs, so maybe strict calibration wasn't too important either?

I haven't tried any significant calibration of anything, only small stuff that (hopefully) doesn't throw off the rest of the scope (e.g. adjusting the invert balance on channel #2, and recalibrating the V/div balance). I haven't touched the sweep timing calibration, for example, because I know that would require equipment that I just don't have.

My impression (from this group and elsewhere) is that you can still get these things calibrated by professional shops around the country (the place I'm looking at is www.custom.cal.com which has locations in New Jersey, Florida, and Oregon), and that it's not absurdly expensive (but more expensive than the old scopes themselves). I'm not sure what, if any, the extra cost is for a traceable cert.

I'm pondering the same thing you are pondering, if only because it would be a possible way to defray the cost of acquiring these parts scopes. Also, I only need so many parts scopes, and I'm well beyond that number right now. I also need only so many working scopes, and I am probably beyond that number as well. I'm not sure what obligations you are under if you sell a scope as "working" or "restored". If I were going to charge the kind of prices I still see for "working" 475a on eBay, I would want to include at least a front cover, pouch, probes, and operators manual, and the scope would have to be in pristine cosmetic condition (but that's just me and my ridiculous scruples).

The number of working scopes I need is a complicated question: While the 475 and 475A are on the bench (as subjects) I need a scope that I can use to work on them, which should be a 100 MHz scope (the 2236). However, the 2236 is currently on the bench (as a subject) so I need a scope to work on that one as well (which is either my father's old 2213, or the 2215A). The 2213 could also be on the bench, but I've given up trying to diagnose its intermittent channel 1 flakiness, so the 2215 is the primary scope for the moment, and everybody else is either a patient or a donor.

-- Jeff Dutky


Re: I give up.

Chuck Harris <cfharris@...>
 

Postal money orders are a bit problematic.

The banks won't cash them.

The post offices will only cash them if they
have enough money in their drawer.

Since COVID, most folks are using credit cards,
so that is almost never if it is a big money order.

Otherwise they work great.

-Chuck Harris

snapdiode via groups.io wrote:

Good old postal money orders still work...






Re: I give up.

snapdiode
 

Good old postal money orders still work...


Re: CRT static charge

stevenhorii
 

Isn't the buildup of static charge the reason CRTs get dusty - attracting
dust - and also why sitting in front of a CRT TV or computer monitor bad
for those with allergies?


On Mon, Dec 7, 2020, 14:18 Ed Breya via groups.io <edbreya=
yahoo.com@groups.io> wrote:

I second Eric's suggestion, especially regarding the "back of the hand"
test, which makes a great static charge detector. With a small CRT like in
a scope, you can just place your knuckles against the CRT face.

If the CRT lights up and seems to operate normally, then eventually the
sound should go away as the static charges in the materials equalize. The
root cause may be that you did too good of a job cleaning the face parts. I
have often said that dirt and grime can be your friend, when it comes to
static electricity problems. After a CRT has been in service for a while,
ambient moisture and particles form a natural static discharge path on the
surfaces. If you've used an anti-static wipe on the plastic shield, that
should have similar effect. Maybe try the same on the CRT glass face too,
and be sure both sides of the plastic shield are treated.

Of course, this all assumes the sound really is just discharge at the
face. If it's something else inside, then it's a different story. Try
looking at the scope, opened up, in the dark. Sometimes you can see
discharges around the HV parts. Also, if there's enough, you can smell
ozone and nitrogen oxides in the vicinity.

Ed






Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

Dave Peterson
 

I'm talking about going through the instructions in section 5 of the 465 manual.

Calibration is definitely a loosely used term here. I'll only have a function generator, a DMM and a "working" existing 465 scope.

I was thinking about opening a calibration conversation with you. I suspect you're familiar with real calibration considering your father was using these scopes for real work. I'm sure he had to send them to a certified calibration lab every six months. Does such a lab even exist for these old scopes anymore? I doubt it. In other words, I doubt a strict certified calibration of these scopes is ever possible anymore. And calls into question the concept of full/"certified" restoration. It's all hobbiest restoration at this point anymore. I suspect.

If I resell a parts scope as "restored", what does that mean? It's a rhetorical question I'm pondering for myself at this point.

Dave

On Monday, December 7, 2020, 12:06:05 PM PST, Jeff Dutky <jeff.dutky@gmail.com> wrote:

Dave,

When you say "calibration" are you actually doing a full calibration on this scope -- do you have the full set of calibration equipment -- or are you doing something more abbreviated?

-- Jeff Dutky


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

Dave,

When you say "calibration" are you actually doing a full calibration on this scope -- do you have the full set of calibration equipment -- or are you doing something more abbreviated?

-- Jeff Dutky


Re: CRT static charge

Ed Breya
 

I second Eric's suggestion, especially regarding the "back of the hand" test, which makes a great static charge detector. With a small CRT like in a scope, you can just place your knuckles against the CRT face.

If the CRT lights up and seems to operate normally, then eventually the sound should go away as the static charges in the materials equalize. The root cause may be that you did too good of a job cleaning the face parts. I have often said that dirt and grime can be your friend, when it comes to static electricity problems. After a CRT has been in service for a while, ambient moisture and particles form a natural static discharge path on the surfaces. If you've used an anti-static wipe on the plastic shield, that should have similar effect. Maybe try the same on the CRT glass face too, and be sure both sides of the plastic shield are treated.

Of course, this all assumes the sound really is just discharge at the face. If it's something else inside, then it's a different story. Try looking at the scope, opened up, in the dark. Sometimes you can see discharges around the HV parts. Also, if there's enough, you can smell ozone and nitrogen oxides in the vicinity.

Ed


Re: CRT static charge

 

Dave,

You might also be noticing it now because of a change in humidity. Higher humidity air is better at bleeding off the static charge from the face of the tube than low humidity air, so you are more likely that get that crackling noise in the winter than in the summer.

This is an effect that was very well known in the days of CRT TVs, and I remember it as one of the distinctive auditory experiences of using TVs back then (that and the sound of the flyback transformer). I just tried one of my Tek scopes, and I didn't get any crackling on power up, nor do I feel any static field holding the back of my hand near the tube face, but it may not be very dry yet here in Maryland, and the implosion shield may block some of the static field that I would otherwise be able to detect by hairs standing up on the back of my hand.

-- Jeff Dutky


Re: CRT static charge

Dave Peterson
 

OMG, that's so funny. I totally forgot about that. As soon as my eyes landed on that bit about old TVs my brain jumped back to 1970 and the crackle that accompanied twisting the power/volume knob on the TV flooded back into my mind. Thanks for that old memory! Oh yeah! CRTs! It's been a long while. Perhaps that's part of the nostalgia and joy of old oscilloscopes.
Dave

On Monday, December 7, 2020, 10:44:27 AM PST, Eric <ericsp@gmail.com> wrote:

IMHO that is very normal and a product of the accelerating voltage in the CRT. If it was arcing out of the tube there would be no vacuum left in the tube and  the tube would be bad. All my 7000 series scopes do it and the old tube TV’s used to do it. I used to check the high voltage section of a tv by just running the back of my hand over the the tube about and inch off the face, no dissemble needed. If the hairs on my arm stood up the HV section of the TV was good.

Eric
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Dave Peterson via groups.io
Sent: Monday, December 7, 2020 1:36 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] CRT static charge

Thanks Raymond. I figured when dealing with voltages with a "k" suffix it's probably wise to be safer than sorry-er.

Dave
    On Monday, December 7, 2020, 10:32:23 AM PST, Raymond Domp Frank <hewpatek@gmail.com> wrote:

On Mon, Dec  7, 2020 at 07:29 PM, Dave Peterson wrote:


Is this normal?

Could it be an indication of anything untoward?
Short answer to your two questions: Yes, it is, and No, it isn't.

Raymond


Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

Dave Peterson
 

Yes, intermittent transient problems are the worst.

I figure any recovered parts scope comes with 0 assumptions. When it at first did nothing I wasn't the slightest bit surprised. I was more surprised that it did work - and is working pretty darn well. My primary guess is that the "Regulating Range Selector" - the jumper in the main fuse holder? - was the culprit. That removing and reinstalling it broke whatever surface corrosion was interfering. The power switch had already been cycled a few times (without power) during the disassembly/reassembly process. Should it be taken back out and and cleaned? Sure, along with every other contact surface in the scope? I'm not that patient and thorough, yet.

It's doing a lot of off-nominal things that can't be of any surprise: pots being "jumpy", etc. I have to wonder how long this thing has been sitting on a shelf in the most non-ideal conditions. There have been a lot of water spots on internal metal parts. I think mostly likely condensation. The boards have appeared rather pristine, though it also appears to have had some boards and shields removed. Obvious solder work on the wires and BNCs necessary to disassemble/reassemble. I suspect several attempts to fix it have been made before.

Things are cleaning up as I use it - position pots are settling down with use, BNCs are being noisy and intermittent, but getting better. Small oxidation and corrosion on contacts has to be expected. I'll get into cleaning methodologies as I get into the calibration and determine what is and isn't working.

Just part of the fun!
Dave

12041 - 12060 of 186209