Date   

Re: let's bring this back to life Re: Tektronix 453 high voltage problem

John
 

The HV circuit takes less than 500mA when healthy: current is inversely proportional to the DC voltage in (unregulated, but normally around 16 to 17V raw DC).
I wouldn't recommend removing the diode D940 and then powering the rest, in case you end up with +ve grid volts.
Have you eliminated C953/C961 by just lifting C954 and powering?
I'll send you some useful component location info.
John


Re: Help needed with no trace no beamfinder on 465 (not b)

Brendan
 

If I decide to go that route, are there any
of you here that would like the parts? (easily mailed boards and whatever).

Advice?
Im on the lookout for a parts scope for my 465. Let me know the price,if thats the way you decide to go.


Re: Help needed with no trace no beamfinder on 465 (not b)

 

Thanks for correcting me Albert, I apologize for being so sloppy... I have corrected the legend on that photo to read 10V/div after I rechecked. And you are correct as well about my not having checked the dc bias on the first one. On ac coupling it is pretty identical to before.

So, evidently there is no significant difference after exchanging the Q1418.

I'm wondering now what my next path should be. Unlike many of you on this forum, I am not wanting to repair this for fun, but rather I want to be able to use the scope, as I feel it would be a more versatile scope than the 2213A that I'm using. But it seems we have gone over much of the circuit with little gained. Another option for me might be to work instead on fixing my 464, but it has the same problem (no trace no dot) and I don't need the storage functionality. I might be tempted to swap the HV mulitplier or the T1420 transformer from the 464 to the 465, but that's a lot of work and there is of course a fair chance the one or both of those are what's wrong with the 464- and we haven't been able to narrow the problem down to those parts anyway.

And honestly... I have been so frustrated working on this (obviously above my skill level, and it has taken many hours) that I am tempted to simply part them both out so that I can get back to the projects I want to work on (unrelated to fixing Tek scopes). If I decide to go that route, are there any of you here that would like the parts? (easily mailed boards and whatever).

Advice?


Re: Tektronix RAMS (Surplus) Store - Odd hours?

Dave Brown
 

I am not associated with RAMs but volunteer next door at the vintageTEK
museum. RAMS main purpose is recycling. They run the store as part of that
purpose but they likely do not have the resources to man the store for more
hours. When I go there sometimes in the last half hour they are open to the
public there aren't a lot of people there buying. People tend to line up
before the store is open so I suspect their business is very front loaded.
I suspect there is no business case for longer hours.



Dave


Re: Tektronix 2235 small/not work trace line move

Andrey Ulyanchenko
 
Edited

Thank you ! My work is done. After replacing all 150 ohm resistors (1% 2W), the beams appeared and are normally adjusted to the full height of the screen .. After that, the capacitor was completely replaced in the power supply. Slightly spread out by focusing the beam. At maximum brightness, the beam is slightly defocused, most likely the CRT resource is already very small. Tell me how to check the CRT? Thank you . Photo will be added in album.
Also my video with some ripple at the top of the calibration signal on youtube https://youtu.be/u_AA_C2UYNM


Re: 2215 sweep knob : looking for the locking hardware

Vincent Trouilliez
 

On Fri, Jun 15, 2018 at 07:30 am, tom jobe wrote:
Does anyone around Los Angeles have a a 2213 or 2215 knob and and related
parts that I could measure?
I just took some measurements of the broken part :

- Overall length : 8.6mm
- Outside/largest diameter of the tapered/conical part : 6mm
- Height of the tapered section : 5mm
- length of the threaded part : well given the above numbers, that's 8,6 minus 5, so about 2,6mm long.

Knob : inner diameter, where the collet needs to fit : 5mm, by 6,5mm long.

Splined shaft diameter : imperial size again.... not 3.0mm but 3.2mm, hence a 1/8". A metric 3mm collet could probably be enlarged with a drilled bit... or possibly fit as is.

Obviously the collet needs to be hollow so that the inner/tiny shaft for the red little uncal knob, can traverse it.

If anyone has a part that fits the bill, from whatever old knob laying around...


Vincent Trouilliez


Re: Wierd 422 No Signal Trace

 

OK, I found the picture. I think you are right but not sure of exactly where to look at the moment. You have full sweep yet it does this, somehow that ripple is getting to a lower level stage. I could be wrong, but since you said it is not there on external, it has to have something to do with the ramp generator.

If you have this resolved let us know, but assuming it is on the back burner...

It would be interesting to know if the aberration is magnified in the X10 mode on the horizontal. Also, on channel 2, does it invert when you switch to invert ? Might be useful info, might not but it is easy to find out.

I assume you do not have the AC/DC option, if so any 120 Hz ripple would affect more than just this because it is an SMPS. All sources would be drooping. I think you just have one source drooping.


Re: Help needed with no trace no beamfinder on 465 (not b)

Albert Otten
 

Keith, I think the Q1418 collector waveform is taken at 10 V/div, not 20 V/div. The 15 V(unreg) comes from the bridge rectifier I suppose, where the schematic says ~~ 24.5 V. You didn't show or mention the collector DC level when using the "old" transistor. Does this correction (when I am right) make the results more comparable?
Albert

On Thu, Jun 14, 2018 at 02:45 pm, Keith Ostertag wrote:


So... getting back to it... After replacing Q1418 with a unit from a 464 that
I have (also has a CRT fault).

Q1416 shows very similar traces, all three the same (EBC), but now at about
150mV p-p (previously about 120mV p-p).

The big change is Q1418 traces. There's much more DC bias now on the
collector. See here:
https://groups.io/g/TekScopes/photo/49286/11?p=Name,,,20,1,0,0

Current through F1419 still about 160mA.

HV tp is around -72V.

So... ??? Not sure how to proceed.


Re: My 422

keantoken
 

If a transistor has been degraded due to reverse Vbe, you can actually restore it's Hfe by applying high base current to heat up the junction sufficiently. Might be fun to try. On Friday, June 15, 2018, 1:53:55 PM CDT, Jeff Urban <@JURB> wrote:

Hey Renee, I was just reading on sci.electronics.design about transistors degrading over time when they get alot of reverse Vbe. Actually they were talking about exceeding the rating or the transistor but how is that rating determined ? They obviously test it destructively and don't take 20 years to do it. So I think it possible that it could degrade even if the rating is not exceeded. Looking at the circuit, it might have quite a negative spike in the base drive.

I tried to measure the rise time but I am not 100 % sure of the scope. (one of the reasons I want the 422 running). I am not sure of the geometry, as in \_\ vs. /_/. I also made no attempt to measure the fall time when the transistor turns on. The Miller effect causes the rapidly falling collector voltage to get to the base and fight the base current. It also increases whatever negative spike.

Hmmm, just thought of something, I could use the 422 to cop the waveform from the 422. Why not ? It's not like trying to tickle yourself. It works well enough (once I get that filter in that poofed on me) to take waveforms in itself. The only time I guess you couldn't is trying to view a waveform in the same vertical channel you're using. But conceivably in channel one you could view channel 2 and vice versa. I want in the power supply, there should be no problem. I have alot more confidence in the Tek than my elcheapo daily driver scope. Eventually I am going to end up with a 7000 series, I can smell it. I think I can talk my buddy out of the 7603 if I get his 7834 up to snuff. But he has been too busy to do anything so, oh well.

Turn off time is most important  with an inductive load, but turn on time is also important. I already measured the saturation voltage and it is low enough, at least by my (hopefully accurate) math. Turn on time is not as critical of course with the inductive load, but it does matter.

The design may be flawed. (the hell you say !) It is possible that at higher input voltage when the regulation is kicked in more, that the forward base current drops. I dunno, but it doesn't seem to be turnoff time, it doesn't seem to be the saturation voltage, when else could this dissipation be happening ? Leakage when off ? Well I see maybe what, 50 volts there ? Even at 10 mA that's only 50 mW.

I might just wire in a pair of 2SD427s I THINK I got and I do have a heatsink. you might want to try that with the 2N3055s. All you need is a piece of metal, a drill and for 50 measly volts you can use wax paper for an insulator, or use 2 pieces of metal and don't worry about insulation for now. I happen to have a bunch of heat sinks around but you don't want a 1,200 cm^2 thing for the test because the 422 doesn't have that. In fact the 422 doesn't even have any vent holes. It was designed to be rugged. A Tek rep told me years ago he saw one that had gone down a hill in a car rolling and it looked much better than the car. I also read that someone had grabbed one and slammed it hard on a table repeatedly and there was no damage. If ruggedness was their goal I guess they wouldn't want a spill or a few raindrops destroying their masterpiece.

And it is a masterpiece. Madman Muntz would be proud. Other than the power supply it only has I think 49 transistors in the whole thing, 3 nuvistors and a couple HV regulator tube. I think that on top of good engineering, Tek has had better CRTs. I think they make their own. Check out :

https://www.youtube.com/watch?v=G0Dci5RPe94

when you have  spare half hour. And I was 7 years old at that time.

Muntz was a TV maker who used so few tubes that other engineers said there is no way in hell it could work. He is said to have walked around the prototype department and just remove parts from the units until they quit working. I think wiki has a page on him.


Re: My 422

 

Hey Renee, I was just reading on sci.electronics.design about transistors degrading over time when they get alot of reverse Vbe. Actually they were talking about exceeding the rating or the transistor but how is that rating determined ? They obviously test it destructively and don't take 20 years to do it. So I think it possible that it could degrade even if the rating is not exceeded. Looking at the circuit, it might have quite a negative spike in the base drive.

I tried to measure the rise time but I am not 100 % sure of the scope. (one of the reasons I want the 422 running). I am not sure of the geometry, as in \_\ vs. /_/. I also made no attempt to measure the fall time when the transistor turns on. The Miller effect causes the rapidly falling collector voltage to get to the base and fight the base current. It also increases whatever negative spike.

Hmmm, just thought of something, I could use the 422 to cop the waveform from the 422. Why not ? It's not like trying to tickle yourself. It works well enough (once I get that filter in that poofed on me) to take waveforms in itself. The only time I guess you couldn't is trying to view a waveform in the same vertical channel you're using. But conceivably in channel one you could view channel 2 and vice versa. I want in the power supply, there should be no problem. I have alot more confidence in the Tek than my elcheapo daily driver scope. Eventually I am going to end up with a 7000 series, I can smell it. I think I can talk my buddy out of the 7603 if I get his 7834 up to snuff. But he has been too busy to do anything so, oh well.

Turn off time is most important with an inductive load, but turn on time is also important. I already measured the saturation voltage and it is low enough, at least by my (hopefully accurate) math. Turn on time is not as critical of course with the inductive load, but it does matter.

The design may be flawed. (the hell you say !) It is possible that at higher input voltage when the regulation is kicked in more, that the forward base current drops. I dunno, but it doesn't seem to be turnoff time, it doesn't seem to be the saturation voltage, when else could this dissipation be happening ? Leakage when off ? Well I see maybe what, 50 volts there ? Even at 10 mA that's only 50 mW.

I might just wire in a pair of 2SD427s I THINK I got and I do have a heatsink. you might want to try that with the 2N3055s. All you need is a piece of metal, a drill and for 50 measly volts you can use wax paper for an insulator, or use 2 pieces of metal and don't worry about insulation for now. I happen to have a bunch of heat sinks around but you don't want a 1,200 cm^2 thing for the test because the 422 doesn't have that. In fact the 422 doesn't even have any vent holes. It was designed to be rugged. A Tek rep told me years ago he saw one that had gone down a hill in a car rolling and it looked much better than the car. I also read that someone had grabbed one and slammed it hard on a table repeatedly and there was no damage. If ruggedness was their goal I guess they wouldn't want a spill or a few raindrops destroying their masterpiece.

And it is a masterpiece. Madman Muntz would be proud. Other than the power supply it only has I think 49 transistors in the whole thing, 3 nuvistors and a couple HV regulator tube. I think that on top of good engineering, Tek has had better CRTs. I think they make their own. Check out :

https://www.youtube.com/watch?v=G0Dci5RPe94

when you have spare half hour. And I was 7 years old at that time.

Muntz was a TV maker who used so few tubes that other engineers said there is no way in hell it could work. He is said to have walked around the prototype department and just remove parts from the units until they quit working. I think wiki has a page on him.


Re: 2215 sweep knob : looking for the locking hardware

Vincent Trouilliez
 

Hi Tom,

Thanks for the kind words, I am glad you like my repair topic on EEVBlog... not everyone can stand my long winded posts.. seems Sir "oldway" certainly did not, as you might have read over there... Oh well you can never please everyone can you...

The little part you need would be quite simple to make (and to improve upon)
Do you have experience with machining little parts ?! ^^
I can see how it can be made... but still one would need a suitable lathe and cutting tools to do it, and of course lots of hand on experience to actually get it right... I don't fit that bill sadly.. do you ?! ^^

Still, that would be a lot of trouble :-/

I made progress though : spent some time on the web. Google found me a few sites that sell knobs. Had a look at a few of them.. 99% of the knobs for sale are of the "set screw" type... but eventually I found one that sold the type I need.

Seems these knobs are referred to as being "Collet" type knobs. So I ran a new search for this term, and found this site that sells some, and gives accurate technical drawings of the collet piece that I need, for every size knob that they sell...

https://www.elma.com/en/products/rotary-switches/knobs/product-pages/classic-collet-knobs-detail/

So maybe the easiest would be for me to take measurements of the Tek collet : shaft diameter, overall length, length of the tapered part, and length of the threaded part.
Then I could see if I can find some company on-line that sells these parts. Failing that, I could just buy some random collet type knobs, the ugliest, cheapest, crappiest I can find (hence dirt cheap) just so I can salvage the collet from them. Would take a few different models and sizes (all with the correct shaft diameter of course), and chances are that one of them would fit, or could be made to fit with minor rework/hassle (like shortening the threaded part if need be).
Obviously the thread pitch on the Tek collet must be imperial as well, given that the nut is imperial... however I don't have to stick to imperial, since the replacement collet would come with its own matching screw of course. Yes... it would make the scope non-original and all that... but it would be invisible anyway, and I am not THAT much of a purist... hell, the replacement electrolytic caps I will put in the SMPS ARE visible... yet I can't imagine someone suggesting keeping the old caps in place forever, just for the sake of originality !

So, "collet" is the word of the day for me...


Vincent Trouilliez

if one had some accurate dimensions from a 2215 knob, shaft and the original
part that is broken.
I have lots of 22xx scopes, but they are all from the more common 22xx family
of smaller size scopes which would include the 2215A, which is very different
from the 2215.
Also, I do not know anyone who has a 2213 or 2215 near me that I could get the
measurements from.
Does anyone around Los Angeles have a a 2213 or 2215 knob and and related
parts that I could measure?
tom jobe...


Re: Tektronix RAMS (Surplus) Store - Odd hours?

 

Hi Bruce,
I think what you really are asking is what I ask every time I am going down to Beaverton: "why can't the Country Store be open when it is convenient for me because I happen to be in the area."

I think the answer is obvious. The store loses money. Being open twice per month is all they need to satisfy their regular customers (Ex-Tek employees) and just about everybody else.

Tek isn't interested in dealing with walk-in traffic for lots of reasons:
1) There is no reason to be open more often. If you are there on one of those days you would see there is only a very small group of people waiting to go in and they are mostly Ex-Tek people. So there is no reason to add more hours.
2) It is expensive to be open. You need someone (two people actually) to keep an eye out for people stuffing their pockets with small parts that have significant value.
3) Walk-in customers are a pain in the ass. I know because I am one. I will automatically ask them to lower the price enough on something I want so I can buy it.
4) Online sales via Ebay or whatever else they use are more cost effective because they can list big ticket items there.

Dennis Tillman W7PF
"Quando Omni Flunkus Terra Retreatum"

-----Original Message-----
From: Bruce Lane Sent: Friday, June 15, 2018 8:26 AM

Fellow Tekkies,

I've gotten curious about the rhyme or reason to the RAMS store's
limited public hours (two Thursdays a month, less than half a day).

Thoughts on this?

Thanks much.

--
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)


--
Dennis Tillman W7PF
TekScopes Moderator


Re: Tektronix RAMS (Surplus) Store - Odd hours?

bobh@joba.com
 

Yup, about 49 years that I recall, when it was at Sunset. It sure gives you time to stew over the ones that got away.
Bob.

-----Original Message-----
From: Ed Breya via Groups.Io
Sent: Friday, June 15, 2018 9:07 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tektronix RAMS (Surplus) Store - Odd hours?

I think it's always been like that, even in the good old days. I recall it was only open Saturday mornings way back, with similar limited hours. The store is only a small part of the operation - they have a lot more and bigger stuff to deal with, and the occasional open hours are probably about right to get rid of the small items to individual buyers.

Ed


Re: Tektronix RAMS (Surplus) Store - Odd hours?

Ed Breya
 

I think it's always been like that, even in the good old days. I recall it was only open Saturday mornings way back, with similar limited hours. The store is only a small part of the operation - they have a lot more and bigger stuff to deal with, and the occasional open hours are probably about right to get rid of the small items to individual buyers.

Ed


Tektronix RAMS (Surplus) Store - Odd hours?

Bruce Lane
 

Fellow Tekkies,

I've gotten curious about the rhyme or reason to the RAMS store's
limited public hours (two Thursdays a month, less than half a day).

Thoughts on this?

Thanks much.

--
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)


Re: 2215 sweep knob : looking for the locking hardware

tom jobe <tomjobe@...>
 

Hi Vincent,
The EEVblog 2215 post, that you gave us the link to, is excellent!
The little part you need would be quite simple to make (and to improve upon) if one had some accurate dimensions from a 2215 knob, shaft and the original part that is broken.
I have lots of 22xx scopes, but they are all from the more common 22xx family of smaller size scopes which would include the 2215A, which is very different from the 2215.
Also, I do not know anyone who has a 2213 or 2215 near me that I could get the measurements from.
Does anyone around Los Angeles have a a 2213 or 2215 knob and and related parts that I could measure?
tom jobe...

On 6/14/2018 1:02 PM, Vincent Trouilliez wrote:
Hi Group,

I am working on fixing a 2215 scope I bought the other day.

http://www.eevblog.com/forum/repair/tektronix-2215-scope-repair/

Didn't power up.. that's now fixed, was a dodgy Zener diode in the pre-regulator board of the SMPS. While waiting for new caps to arrive to recap the SMPS, I thought I would give it a good clean and pamper it. I need a little help finding a little mechanical part that broke.. :-/

It's the "screw" (not the usual lateral/set screw arrangement, but the central/concentric type screw) that holds the delayed sweep knob onto its shaft :

http://www.eevblog.com/forum/repair/tektronix-2215-scope-repair/?action=dlattach;attach=453070;image

Knob itself is fine. It's just the metal piece/"chuck", tapered, threaded, that bites the splined shaft when tightening the central nut... that I need. This appears to be made of the softest metal Tek could get... no, I swear I didn't use a hammer to tighten it... but still, the threaded part broke.

So if someone has a box of old stuff and maybe have this little part that would save this knob (from a different scope model possibly ?)... I would be very grateful indeed ! :-)

With some luck, does anyone know if this might possibly be some generic piece of hardware, that one could buy from god knows what hardware vendor on-line ? (any links appreciated ! )

What would be a correct name/terminology to describe this part, so I can use the appropriate keyword to try to find some ?
Hopefully one can get one made from a stronger metal...

Thanks for reading anyway....


Regards,


Vincent Trouilliez


Re: Up to date capacitor list for Tek 2465A and 2465B scopes (2018)

Chuck Harris
 

You didn't listen to what I said about the electrolyte.

Isopropyl alcohol does tremendous "corrosion" to a styrofoam
cup, but nothing to a piece of aluminum.

The corrosive, to copper, electrolyte in 105C capacitors makes
a mess out of copper, but does nothing to aluminum and aluminum
oxide. An electrolyte can be corrosive to one material, and
totally benign to another.

Years ago, the electrolyte ate the aluminum oxide dielectric
layer. This is why a capacitor from that era needed to be
reformed periodically if you wanted it to meet its nominal
specifications. Today, capacitor plate material is precision
anodized in bulk form, wound up into a capacitor, and given a
highly electrically conductive electrolyte (low ESR) that does
not corrode the aluminum oxide dielectric deposited during the
anodize process.

You may have heard about the counterfeit electrolyte that
appeared in many electronic devices, notably computers, in
the late 90's. This was a case of an electrolyte being used
that was not as noncorrosive as was necessary.

When you operate a modern electrolytic capacitor on lower than
its nominal voltage rating, it is not harmed, and it does not
change in any way.

Ever wonder why today's capacitors are so much smaller for the
same C x V product than were the capacitors originally installed
in the scopes? The reason is the better processioning of the
aluminum plate material allows far fewer errors in dielectric
thickness, and the greatly improved non corrosive to aluminum
oxide electrolyte allows the manufacturer to use a lower voltage
safety factor than before.

Today's 25V capacitor is yesterdays 50V capacitor.

If the electrolyte was as corrosive as you imagine, my bags of
NOS capacitors would have all eaten away their aluminum oxide
dielectric and all be short circuit. They are not. They are
as good as the day they were made. Electrolytic capacitors from
40-50 years ago would be long gone in similar circumstances.

You are limiting your choices based on imagined problems.

-Chuck Harris

OBTW, Nichicon of 1975 is a far different company from Nichicon
of 2018. Dare we compare Tektronix of 1965 to the Tektronix of
today? Neither company has any of the original founders, nor
their instincts for quality, involved today.



M Yachad wrote:
Chuck

“If you need some evidence to back my assertions, grab any old bag of electrolytic capacitors that have been sitting on the shelf for years, and measure the capacitance. They will all measure at the nominal value... after years of being operated at the extremely low voltage of 0V. “

Not sure if you’re trying to be funny, or if you’re serious.

If you’re serious, I think your comparison is irrelevant. Unless a capacitor is in a working environment, coping with heating and cooling cycles, you cannot compare it to a shelf model, no matter what voltage. And statistically, throwing a single bag of old undocumented caps into the ring here, is irrelevant.

“I have just such a bag of nichicons from a project where I overbought the caps. This was back in the 1970's. They all still read 2200uf +/- 10%.”

In the best case, it just goes to prove that Nichicon is still the right choice, today.
...


Re: Up to date capacitor list for Tek 2465A and 2465B scopes (2018)

 

Chuck

“If you need some evidence to back my assertions, grab any old bag of electrolytic capacitors that have been sitting on the shelf for years, and measure the capacitance. They will all measure at the nominal value... after years of being operated at the extremely low voltage of 0V. “

Not sure if you’re trying to be funny, or if you’re serious.

If you’re serious, I think your comparison is irrelevant. Unless a capacitor is in a working environment, coping with heating and cooling cycles, you cannot compare it to a shelf model, no matter what voltage. And statistically, throwing a single bag of old undocumented caps into the ring here, is irrelevant.

“I have just such a bag of nichicons from a project where I overbought the caps. This was back in the 1970's. They all still read 2200uf +/- 10%.”

In the best case, it just goes to prove that Nichicon is still the right choice, today.

“But, alas, what you say is not true. It once was, back when electrolytic capacitors used rather caustic electrolytes that ate away the aluminum oxide dielectric layer, but that hasn't been the case for about 30 years.”

On the contrary, the low-ESR capacitors of today DO contain corrosive electrolyte.
Do I need to expound on the A5’s damage?

Read up on Chemicon’s recent hard lessons on their KYx KZx and LXx series, with the problems, and subsequent requirement to reformulate the highly corrosive electrolyte.

We only get to know about these problems, LONG AFTER the caps have been installed in the customer’s machine, and he has paid for them.
So why not anticipate the problem, and plan for it?

Therefore, there is enough empirical evidence to support the postulation that the issue STILL exists today.
And I simply do NOT see this as a problem.
We can choose to ignore it, or we can choose to plan our BoM, with the knowledge that a poor choice may bite us in the future.
My way to deal with this exact issue, is to suit the capacitor voltage rating to the actual circuit voltage.
Is that such a difficult decision to make?
To me, it’s simply preempting the possible problems which corrosive electrolytes cause.

It’s a free world.
I choose the path of caution and reliability – I have customers to answer to, and my hard-won reputation to uphold.

A man who’s rebuilding his own scope can throw whatever he wants in there – the only one he needs to answer to, is himself. And in that case, to him, this discussion is irrelevant.

“Just like it was fine when you specified 330uf 50V caps to replace both the 250uf 20V and the 180uf 40V caps in the power supply.”

You’re right – in my PDF, I did say that. I did not pay sufficient attention during my proofreading to differentiate. However, after that PDF was published, there was a lot of positive feedback on this forum, pointing out the errors and suggesting the changes which should be made. All of those changes are included in my ebay repair kit, which has sold nearly 200 units, the vast majority of them not on ebay.

“This isn't audio gear where you have to worry about how the end user might "feel" about your choice. You can use valid technical reasons.”

I’ve been around much too long to give much thrift to what people “feel” about my conservative way of life, much less to audiophools who chase after every new bottle of snake oil. My principle is “First reliability, then sound”. Why? If the machine doesn’t work, then what worth are all the salesman’s promises on the superior sound which it is supposed to it deliver?

G-d bless you all for your input – it’s what keeps this forum alive and each of us learning more as we go along.

Menahem


Re: S6 Sampling Head Bridge Cavity Question

 

On Thu, Jun 14, 2018 at 11:42 pm, Dennis Tillman W7PF wrote:


I have absolutely no idea how you tell when either of the two output barrels
are touching the substrate. The only way I think Tek did it was by applying
strobe signals and monitoring the output on the center conductor of the
barrels. As I turned them I kept hoping for some change in resistance
between the center conductor of the barrel and the 5 pins that go into the
cavity. I never got a reading of any kind. In the end I failed to get any
output at all from the head when I was done. It was dead.
Dennis,
This from a Maintenance Note from June 74:
//S-6 SAMPLING HEAD INTERMITTENT OUTPUT
In the past the S-6 Sampling Head has had an Intermittent problem in the Hybrid Bridge Circuit.
The center conductor of the 3mm connector on the front panel connects directly to the bridge sub-strate
via a mechanical spring loaded plunger. The Intermittent output Is caused by the plunger. Norm Farmer of
the Rockvllle Service Center has suggested a field fix which entails cleaning the plunger. When you re-Install
the spring and plunger make sure the plunger is free enough not to bind up when pushed all the way Inside
the center connector, yet not so free that it will fall out when you turn the connector upside down. This
practice insures that the center connector makes good contact with the plunger. The front 3mm connector
will be the only one you probably will have to be concerned about. You will need a wrench to remove the
3mm connector. You can do this by increasing the width slightly of a 3/16th open-ended wrench
The 3mm connector spring and plunger are not shown In the S-6 manual. The part number for the spring
is 214-1072-00, and the plunger Is PN 131-0632-00.//

/Håkan


Re: S6 Sampling Head Bridge Cavity Question

Dave Casey
 

The input (loop thru) signals J10 and J12 are 10k from another pin, "O".
The output signals at 16k and a diode drop away from another pin ("J" ->-
J15 or J16 ->- "M"). I feel like this should be measurable with an ohm
meter to see when you're making good contact, but I'm not going to find out
the hard way that it doesn't work that way.

All the manual says is "The assembly female 3 mm coaxial connectors may be
replaced by using a small wrench on the flat portion of the connector to
remove and replace a connector from the assembly." (Page 5-1, second to
last paragraph)

Dave Casey

On Fri, Jun 15, 2018 at 1:42 AM, Dennis Tillman W7PF <@Dennis_Tillman_W7pF>
wrote:

Inside the S6 Sampling Head there are 3 PC boards. One connects to the
socket inside the 7S12, and nothing else. One is the strobe board, and the
third is the preamp board. They are interconnected in a 3D stack using long
pins. But that is not what my question is about.



At the heart of the S6 is the sampling bridge. This diode bridge is
contained on an extremely thin ceramic substrate inside a very substantial
steel clamshell "cavity". Four SMA barrels and 5 pins enter this "cavity".
I
was troubleshooting one of my S6 heads that had a lot of unusual noise.
This
was not sampling noise which would look like a fat cloud of dots instead of
a thin cloud of dots, Instead the sampling was actually very tight but the
trace was jumping up and down randomly as if there was low frequency
"Popcorn" noise affecting it.



After a few hours of troubleshooting by replacing all three boards of the
noisy head with boards from a good head (and vice versa) I knew the problem
was inside the cavity. I thought there might be a loose bond wire or debris
on the substrate that was slightly conductive so I opened up the cavity to
take a look. I found nothing which might be causing the noise.



But when it came time to put the cavity back together I discovered
something
I have never encountered before. Here is where some mechanical genius at
Tek
had to come up with a solution to a an impossible packaging problem. The
barrels cannot be soldered to the substrate since they will be torqued
during the assembly of the sampling head and this would break any
connection
to the delicate ceramic substrate. They have to be free to turn a bit.



At first glance the SMA barrels look like typical Female SMA to Female SMA
Adapters. But on closer inspection one end has a tiny protruding "male"
pin.
The "male end must be screwed into the cavity after it the top and bottom
halves of the cavity have been screwed together. So there is no way to see
what is going on inside the cavity as you screw it in. Somehow (I haven't
got a clue how) you must stop just as the male tip touches the ceramic
substrate and makes contact with it. If you go any further you can damage
the ceramic substrate.



Since both of the barrels coming out to the front of the sampling head are
connected together (the S6 is a loop thru TDR head) you can carefully turn
the barrels until you get continuity from center pin to center pin of each
barrel since the loop thru connection is made on the substrate.



I have absolutely no idea how you tell when either of the two output
barrels
are touching the substrate. The only way I think Tek did it was by applying
strobe signals and monitoring the output on the center conductor of the
barrels. As I turned them I kept hoping for some change in resistance
between the center conductor of the barrel and the 5 pins that go into the
cavity. I never got a reading of any kind. In the end I failed to get any
output at all from the head when I was done. It was dead.



It did seem to eliminate the noise but it eliminated everything else as
well
:(



Does anyone know how Tek did it?



Dennis Tillman W7PF