Date   

Re: 475A Chop Blanking and a Theory Question

Harvey White
 

I certainly can't give you an answer for that, but perhaps a bit of insight into how things might be done.  While I was only a "senior design engineer (i.e: I says do it like this and they does.....) in a few instances, in which cases I was the "ONLY" design engineer (more software than hardware, but still.....)

1) design guidelines come (in theory) from the senior hardware or software engineer.  The overall design concept, adherence to what the customer wanted, and compliance to their specifications) was the responsibility of the "senior systems engineer".  He made the decisions, and others followed them.  In theory, the software and hardware "lead" engineers had to show him that their designs matched the specifications.  Note that this was in a multi-layer military/government contract, so documentation, compliance, and at the very last, functionality, were important.  (yes, cynical I am, been there, saw that, tried to design around it).

2) design teams tend to use approaches that they know work, and hope that they fit the current situation.  I've seen examples of 1) it worked and we're fine and 2) well, that kinda does it....

I suspect that Tektronix had the same kind of outcome.  From what I've heard of HP designs, I think they did the same.

So it's likely that the different scopes did designs based on their specifications, what the designs were capable of, and only innovated when a design didn't meet the spec.  Tektronix may have had different limitations here, but there's likely to be an element of the "we do it like that" built into every product.

I've seen that the horizontal amplifier designs of the 468 (which I have) and the 465 seem to be quite similar.  Same design team? Possible.  I will say that I will reuse a design until it fails, then I rework it.  How much that applies to anyone else, and how much "they" are allowed to do that, well.....

Harvey

On 12/18/2020 8:59 PM, Dave Peterson via groups.io wrote:
What got me about the 485 - I was perusing the 4-series scopes on TekWiki - was that it was released before the 465/475s, but had the separate B-sweep trace. But the Wiki mentions that this feature was on the 465B. I'd forgotten about that, and was probably one of the reasons I preferred the 465B when working with them back in the Army. It made me realize that there's this weird mix-n-match of components and features between them. I realize the 485 is a different animal, and I suspect the separate B-sweep trace is implemented in different ways. The 485 is a full dual-trace system.

After getting into the guts of the 465 directly, and the 475 indirectly, and now the 485 just via the TekWiki description, why is the 465 so extensively implemented in discrete components and lesser bandwidth than the earlier 485 (350MHz) and concurrent 475 (200MHz)? Cost? Size? Weight? All of the above? Sure, I'm sure Tektronix made a market analysis and product development plan. And that these solutions addressed expected markets. Anyone have sales numbers? I bet the 465 cost lest, sold more, and probably made Tek more money.

One of the things that I've realized about being a circuit designer, vs. a system designer, is a lack of market awareness and knowledge. It's fine, I'm not a marketing type, and I don't come at the engineering profession as a product solutions person. I admire people who have the inclination and insight to find and implement market solutions. My interest lies closer to the physics of things. But I do find the product development decisions fascinating. Nobody really builds this stuff for fun. They build it to make money!

Steering it back to the original thread, why are the 465 and 475 chop blanking circuits so different, yet so similar? Seems a product development optimization that didn't happen? But I well know being on the inside of product development for the past 30 years, "you go to war with the army you have, not the one you'd like to have". The reality is likely a mix of planning, accident, and circumstance. It fascinates me to consider I was such a kid pedaling around Beaverton with my friends who's dads were engineers in Tektronix struggling with all these developments and the associated stresses and occupations. Appreciating now the realities of their experiences I was ignorant to as a kid, looking forward to unwrapping my presents under the tree. Some things just never change!

Dave





Re: 475A Chop Blanking and a Theory Question

Dave Peterson
 

What got me about the 485 - I was perusing the 4-series scopes on TekWiki - was that it was released before the 465/475s, but had the separate B-sweep trace. But the Wiki mentions that this feature was on the 465B. I'd forgotten about that, and was probably one of the reasons I preferred the 465B when working with them back in the Army. It made me realize that there's this weird mix-n-match of components and features between them. I realize the 485 is a different animal, and I suspect the separate B-sweep trace is implemented in different ways. The 485 is a full dual-trace system.

After getting into the guts of the 465 directly, and the 475 indirectly, and now the 485 just via the TekWiki description, why is the 465 so extensively implemented in discrete components and lesser bandwidth than the earlier 485 (350MHz) and concurrent 475 (200MHz)? Cost? Size? Weight? All of the above? Sure, I'm sure Tektronix made a market analysis and product development plan. And that these solutions addressed expected markets. Anyone have sales numbers? I bet the 465 cost lest, sold more, and probably made Tek more money.

One of the things that I've realized about being a circuit designer, vs. a system designer, is a lack of market awareness and knowledge. It's fine, I'm not a marketing type, and I don't come at the engineering profession as a product solutions person. I admire people who have the inclination and insight to find and implement market solutions. My interest lies closer to the physics of things. But I do find the product development decisions fascinating. Nobody really builds this stuff for fun. They build it to make money!

Steering it back to the original thread, why are the 465 and 475 chop blanking circuits so different, yet so similar? Seems a product development optimization that didn't happen? But I well know being on the inside of product development for the past 30 years, "you go to war with the army you have, not the one you'd like to have". The reality is likely a mix of planning, accident, and circumstance. It fascinates me to consider I was such a kid pedaling around Beaverton with my friends who's dads were engineers in Tektronix struggling with all these developments and the associated stresses and occupations. Appreciating now the realities of their experiences I was ignorant to as a kid, looking forward to unwrapping my presents under the tree. Some things just never change!

Dave


Re: WTB: 3B4 plug in for RTTY

Brenda
 

Bruce, I have sent you an email. :)

Brenda


Found Option 7 board DC-508

Dallas Smith
 

Hello today,

Hope everyone is doing OK. Found this on Flea-bay - "Tektronix DC508 Resolution Multiplier and Option 7 board DC-508" - for $35 plus S/H. It took me many years to find mine. Just search the quote to find on Flea-bay. I think this is a reasonable deal. Maybe could be used in some other model's? not sure.

Dallas


Re: 475A Chop Blanking and a Theory Question

Tom Lee
 

Hi Dave,

RE: 465, 475 and 485

The 485 actually predates the other two, and is a very different animal. There was very little cross-pollination between the 485 team and the folks who did the other two. There are several nice features of the 485 that I wish were more commonly offered (e.g., a built-in fast pulse gen, and two levels of input protection that make it hard to blow up the front end). Every time the red light goes on, I know that I owe John Addis another beer, 'cuz he's just saved me from a blown scope for the nth time.

The 465 and 475 had some personnel in common, and a lot of informal collaboration. Those two scopes are similar enough that a good understanding of either of them will take you pretty far in understanding the other. Lots of stuff in common, too, making organ transplants feasible in more than a couple of cases.

-- Tom

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

On 12/18/2020 16:09, Dave Peterson via groups.io wrote:
There are too many dimensions to all of this!
A) Ha-ha - ya got me! You don't have to get the first edition. It's just the sight of the red cover conjures night sweats.
B) I was looking at the Bodnar FPG. For the $$ I just have too many fundamental things to get first. Like appropriate 10x probes. Send me off into a whole other tread: vertical system calibration and circuit function. I know what I need to do, but I need two proper 10x probes to measure the preamp output. And just to have an appropriate high impedance probe just for poking around. Alligator clips and banana plugs are not appropriate tools for circuit analysis. I could spend several oscilloscopes worth of $$ on just basic bench equipment. I'm trying to prioritize and pace myself. I honestly am considering building my own FPG. Reading Leo's origin thread on EEVblog gives me ideas. Might be fun.
C) Bandwidth, math, transistors, amplifiers and filters: I want to help, but you're quite capable on your own. I also remember wanting to really grok xtor theory, and after getting into it in school I recall the mental rungs on the ladder of understanding. Again, layers on layers: discrete component topologies as applied in 1970 are not synchronous with deep sub-micron CMOS circuits. I'm not as fluent in Tektronix topologies, but I also do recognize a lot of basic BJT configurations. But then there's Tektronix's weird schematics - relative to my experience. The experienced guys on this forum will give better answers, but I'm re-learning myself and remember "the mysterious black box" that was a transistor. The BJT wiki has some really good descriptions and pictures that jive with those mental rungs. Anyway, there's BJT and FET physics, bias topologies, small signal models and analysis, frequency domain analysis, transfer functions, feedback, op-amps, ... There are a lot of facets to the things being done in these scopes. Compartmentalization and experience. Layers and layers.
D) Sorry, after playing electronic tech for 4 years in the Army: 99% of if is mechanical stupidity. But divide and conquer is the methodology, and I'd say you've got it pretty much down. Not as sexy as it seems from the outside. BTW, I just killed and resurrected my cheap Chinese function generator. I just stopped working a couple hours ago. I walked away in a bit of disgust, but after 5 minuets I went back and unscrewed the cover. After poking around online I got the courage to turn it back on and start checking some basic things - power etc. When I noticed a connector partially in it's socket. That's all it took. None of the voltage probing had anything to do with it. Just that it brought my focus to the innards of the box helping me spot the loose connector. Back in business.
E) I'm just beginning to dip my toes into the Trigger and Sweep circuit descriptions and calibration procedures. One thing I'm observing is a difference between my two scopes' triggering of chop signal observation. I want to figure out why they're behaving differently. The "working" scope has a very stable trigger, the "parts" scope is being a bit finicky. Then it occurred to me it would be helpful to see the chop signal without the blanking. Hmm. Wonder how I could do that?! Thanks to some guy on the TekScopes group I know just the transistor to pull to make that happen. Interesting.
I recall my struggle to understand BJT function, and I sense you have a mix of understanding and uncertainty. I'm re-examining the fundamentals I've gotten away from since being a CMOS jockey. If there are facets of xtor theory and operation that are frustrating you, and you can articulate them, I enjoy helping. I might say stupid things along the way, but I enjoy blundering my way into understanding. Let me know if there's something tripping you up.
F) Here's another one: 465, 475, 485. These are all concurrent designs from Tektronix. Yet they're so different in so many ways, while still being the same in a lot of ways. Did they have some mix of independent, common, and cooperative departments working on these? E.g. Your 475 ALT/CHOP circuit is so different than the 465. Why? Doesn't seem that significant a circuit to have such different designs while being produced at the same time? What's the R&D rationale behind that? Similar things with the 465 and 485 - though I haven't had the chance to delve too deep into it. Just rhetorical thoughts to share. Yet another thread/dimension. I am having fun tho!
Hope you're having fun. I got to have the day off to play today, and hope you're getting to enjoy some time off too. Thanks for sharing your thoughts and experiences. It's helping me as well.
Dave

On Friday, December 18, 2020, 03:11:18 PM PST, Jeff Dutky <jeff.dutky@gmail.com> wrote:
Because everything looks like a bandwidth measurement when all you have is a fast pulse generator I had been measuring the rise time of every scope I have to see if their bandwidth matched their specs, and before I fixed the CHOP blanking problem the bandwidth of the 475A was measuring as something like 175 MHz (rise time of about 2 ns), which seemed very wrong. After fixing the CHOP blanking problem, however, I went back and measured the rise time again, and this time I got a rise time of between 1.5 ns and 1.3 ns, which gives the bandwidth as 233-269 MHz, which seems about right for a 250 MHz scope.

I am at a loss to explain how fixing the CHOP feature could affect the bandwidth of the scope (especially since I didn't have CHOP engaged when I was measuring the rise time), and it's entirely possible that some amount of operator error may be involved, but, as I also measured the rise time of my father's 475 when I got the low bandwidth measurement for the 475A, and found the 475 to be spot on at 200 MHz, I suspect I made both measurements correctly (my notes, sadly, do not tell me enough about what how I set up the scopes to be sure).

I suppose that it's possible that another NAND gate in U340, which contributes to another part of the vertical amplifier system, also had a dirty pin that was causing a bad connection, but I don't see anything like that in the schematic. I'm much more inclined to believe that my boneheadedness (like leaving the 100MHz bandwidth limit pulled out), rather than a dirty pin on U340 was the culprit, but I'd be happy to be proven wrong.

-- Jeff Dutky








Re: 475A Chop Blanking and a Theory Question

Dave Peterson
 

Sorry all, that last response was intended to be direct to Jeff, not the whole group. Disregard.
Dave


Re: Unable to display cursors and diagnostic messages after LPVS "recapping"

 

Rogerio,

I don't actually know anything about the scope you're working on, but looking at the schematic I can see that you would not only need "activity" on pins 8-10 of U2521, but also activity on pins 2, 4, and 5 in order to have any effect on U2620 (and similar for U2530/U2630).

Have you verified that the signals from the MUX chips to the op amps are active?

Have you looked at the output from U2301 (pins 12, 15, and 16) to see if it's counting all 8 possible values?

Have you checked continuity between pins 12, 15, and 16 on U2301 to pins 9, 10, and 11 on U2521?

-- Jeff Dutky


Re: 1S1 sampling bridge GaAs diodes: What alternatives?

Tom Lee
 

Nothing says "Happy Holidays" more joyfully than soldering sampling diodes.

Enjoy!

-- Cheers,
Tom

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

On 12/18/2020 14:57, leonard scheepsma wrote:
Thanks everyone for all feedback/comments. A friend (also active here) managed to find 4 equal versions in his Tek vault, so I think I can slowly prepare for a party!

Merry X-mas and a Happy New Year!

Leonard




Re: 475A Chop Blanking and a Theory Question

 

Because everything looks like a bandwidth measurement when all you have is a fast pulse generator I had been measuring the rise time of every scope I have to see if their bandwidth matched their specs, and before I fixed the CHOP blanking problem the bandwidth of the 475A was measuring as something like 175 MHz (rise time of about 2 ns), which seemed very wrong. After fixing the CHOP blanking problem, however, I went back and measured the rise time again, and this time I got a rise time of between 1.5 ns and 1.3 ns, which gives the bandwidth as 233-269 MHz, which seems about right for a 250 MHz scope.

I am at a loss to explain how fixing the CHOP feature could affect the bandwidth of the scope (especially since I didn't have CHOP engaged when I was measuring the rise time), and it's entirely possible that some amount of operator error may be involved, but, as I also measured the rise time of my father's 475 when I got the low bandwidth measurement for the 475A, and found the 475 to be spot on at 200 MHz, I suspect I made both measurements correctly (my notes, sadly, do not tell me enough about what how I set up the scopes to be sure).

I suppose that it's possible that another NAND gate in U340, which contributes to another part of the vertical amplifier system, also had a dirty pin that was causing a bad connection, but I don't see anything like that in the schematic. I'm much more inclined to believe that my boneheadedness (like leaving the 100MHz bandwidth limit pulled out), rather than a dirty pin on U340 was the culprit, but I'd be happy to be proven wrong.

-- Jeff Dutky


Re: 1S1 sampling bridge GaAs diodes: What alternatives?

leonard scheepsma
 

Thanks everyone for all feedback/comments. A friend (also active here) managed to find 4 equal versions in his Tek vault, so I think I can slowly prepare for a party!

Merry X-mas and a Happy New Year!

Leonard


Re: LF: An up to date eBay price list

Michael W. Lynch
 

Any time an E-Bay or other Advertisement begins with "vintage", "rare" or "collectable" the sellers are many times clueless or greedy and have priced their items way above any reasonable value. Like the recent listing that I was looking at that showed a 465 that obviously had almost all the knobs gone AND many of the shafts were gone as well. So there was no way that this thing was even a good "parts mule" and they were asking something like $175 with "free" shipping to USA only. Sellers can ASK as much as they like, it does not mean they will get their price. I agree with snapdiode, just offer X number of $$ and leave it there.

--
Michael Lynch
Dardanelle, AR


Re: LF: An up to date eBay price list

Keith Erickson
 

I do have 1- “1A1”

Keith

On Dec 18, 2020, at 4:14 PM, David Collier <dc888@tpg.com.au> wrote:

Hi Keith,
I am restoring two 545B's and have for them one working 1A1 and two (not working?) 1S1 plugins. Would love to get at least one more useful plugin, then one 1S1 will be surplus to my requirements, unless kept for spares.

Also have a late made in Holland (with readout and fan) 7603 with two 7A18 (one with DC offset); one 7B53A, and a now surplus working 7B53AN. For this 7603 I would again love to get a fancier plugin like a nice RF spectrum analyser! This 7603 came from Canada; carriage was indeed expensive.

Regards,
David Collier
Canberra






Re: LF: An up to date eBay price list

 

Hi Keith,
I am restoring two 545B's and have for them one working 1A1 and two (not working?) 1S1 plugins. Would love to get at least one more useful plugin, then one 1S1 will be surplus to my requirements, unless kept for spares.

Also have a late made in Holland (with readout and fan) 7603 with two 7A18 (one with DC offset); one 7B53A, and a now surplus working 7B53AN. For this 7603 I would again love to get a fancier plugin like a nice RF spectrum analyser! This 7603 came from Canada; carriage was indeed expensive.

Regards,
David Collier
Canberra


Re: Unable to display cursors and diagnostic messages after LPVS "recapping"

Rogerio O
 

Thank you for the replies.

The cables I had to remove were connected to A5 (J251, J421) and to the GPIB and CTT board.
However, I have checked the all the voltages required by A5 board and they were all present and on spot.

AFAIK, a problem in the cables connected to the GPIB/CTT would not cause this problem .

Consulting the chart " Readout Troubleshooting Procedure", is a little tricky since I can't say if the messages TEST 03 FAIL 01 or TEST 03 FAIL02 were displayed (I can see only the traces, but no messages/cursors) , so I moved the case
NO CURSORS PRESENT.
In this case I should check lines RA6, CA6 , DLY REF1 and CURSOR0 which were:
RA6 - Active
CA6 - Stuck @ 0V
CURSOR0 - Stuck @ -1.3V
DLY REF 1 - sTUCK @ -1.6V

The is a bright spot which flickers in the screen (my guess is that it would be the starting point of the cursor/message display).
It moves from time to time.
Also, a message flickers every 3 min (but it is to fast to be read).

I do not understand how it is possible to have activity in pins 3 and 8/9/10 U2521/U2530 and no activity at DLY REF1 and CURSOR0 since I have already replaced U2620 and U2630.
Have they fried again?

Roger


Re: LF: An up to date eBay price list

Keith Erickson
 

I have a number of 500 series plug ins.

Keith Erickson
Wayzata, MN

On Dec 18, 2020, at 1:58 PM, snapdiode via groups.io <snapdiode=yahoo.com@groups.io> wrote:

When dealing with strangers and haggling about a price, the simple approach is simply "I offer X" and wait for the reply.

There's no need for anything else.

Anyone who has a Tek 500-series can see the value of saving on shipping, for example, or have a parts mule with a CRT...





Re: LF: An up to date eBay price list

snapdiode
 

When dealing with strangers and haggling about a price, the simple approach is simply "I offer X" and wait for the reply.

There's no need for anything else.

Anyone who has a Tek 500-series can see the value of saving on shipping, for example, or have a parts mule with a CRT...


Re: So how does this hobby work now?

Greg Muir
 

Not to harp about Jim Williams but it has been some time since I have looked through articles about him. I think this article more characterizes who he was and his love for older test equipment.
https://www.edn.com/remembering-jim-williams-5-years-later/

Greg


Re: LF: An up to date eBay price list

Roy Thistle
 

On Fri, Dec 18, 2020 at 08:55 AM, snapdiode wrote:


there aren't necessarily bargains locally
Ad says, "This quality test equipment comes with a custom rolling stand, the users manual and 40 [extra?] tubes."
By that statement I surmise, the seller is clueless, or greedy, or both. The big draw, for the audio squirrels is "tubes" and the seller appears to know it.
But who knows... I've seen people asking for far more... and very indignant towards the messenger: when their informed they're dreaming.


Re: 500 scopes n stuff

Jean-Paul
 

Dear Bill: GO FOR IT thats what we are here for!

Please include your location as many are not is USA, pickup only or will ship, conditions etc.

You can upload photos on the photos area but not attach.

We are anxiously waiting your scopes!


(:-:)

-73-
Jon


500 scopes n stuff

William Rice
 

Is there any info on how to conduct oneself if one wants to list some older Tek scopes n bits to let go of?

Is this prohibited on this list? Where can I find the rules for such please?

Thank You All,
Bill
W4MXT

7661 - 7680 of 182461