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Dave,

I've had a search through the CDPC (Common Design Parts Catalog) for the tunnel diodes (Tek PN 151-0386-00) in the 465. The service manual says that they are selected from 1N3718, but the Tek part number is not listed as a selected part (as with transistors, whose part number appears to change from 151- to 156- when selected by Tek internal processes, it looks like diodes change part number from 152- to 153- after selection, but I'm just inferring this from what's listed in the Matched or Selected diodes table on page 12-6 of the CDPC). The CDPC also indicates a different vendor part number, STD927 rather than 1N3718, so I don't know what's up with that.

The specs given for STD927 are a 10 mA part with 25 pF capacitance, which appear (based on the Russian Tunnel Diodes list on TekWiki, ) to be matches to 3I306M, 3I306N, 3I306S, 1I305A, 1I305B, 1I308V, 1I308G, 1I308J, 1I308K, 1I308I, 1I308E, or 1I308D (where the rated current meets or exceeds 10 mA and the capacitance is around or less than 25 pF). Most of those are available on eBay.

I also looked for the Tek PN on eBay and Amazon with no success.

-- Jeff Dutky

Yes, the intensity modulation of the 7A26 trace by the dot-blanking leakage is only noticeable when looking at a signal which is related in frequency to the 7S12 sweep. In my example, I'm looking at the trigger output of a S-54 pulse generator in the 7S12 and the trigger is generated by the 7S12. There is still an issue, however, when looking at signals asynchronous to the 7S12 in that the dot-blanking leakage dims the 7A26 trace significantly, especially noticeable when using delayed triggering.

On Thu, Mar 25, 2021 at 11:25 AM, Dave Peterson wrote:

Pardon if I was speaking too off the cuff and using language or wording that
was inaccurate, misleading, or wrong. I'm a newb at this TekScope thing.

By passivation I meant the material used to fill a TO-72 can. See picture:

/g/TekScopes/photo/262237/0?p=Name ,,,20,0,0,0

Dave,

A picture is worth a thousand words. Thanks for clearing up the questions.

--
Michael Lynch
Dardanelle, AR

I was going to offer to send you the "same device" from a 453, only to discover that it's a 2n3441, i.e. smaller TO 66 case! (The 453 has a shunt resistor across the transistor which is either to assist self-starting or reduce device dissipation, or both).
Unusually, I can buy the 2n3442 much cheaper here in the UK, but I guess postage out to the US would bring costs back up again.

NB your post regarding the 575 testing prompted me to put the 2N3441's test to have a look.
I have two with Tek part numbers, and two I bought about a decade ago from I know not where (now) .
With no base current they al meet the 140V spec, but the non-Tek samples have a lower "knee" (c. 90V) where collector curves head north rapidly when passing collector current. I'll try to post some photos. Not sure what the mechanism is called, but I'd say the transistors couldn't be of much use in this region, at least as linear devices.
John

Could he mean the glass lead seal where the leads exit?


Leon Robinson ?K5JLR

I noticed the same resistor, also open, on my 561B! On Thursday, March 25, 2021, 11:18:00 AM CDT, cmjones01 <chris@...> wrote:

I've just noticed something odd about the calibrator outputs on my
535A scope and 127 plugin power supply. They both have a 0.25R
resistor in series with the calibrator socket's ground connection. The
reason I noticed is that the 127's resistor is open-circuit, so
connecting the calibrator to another piece of equipment left the
ground disconnected, with the expected symptoms.

I couldn't find any information in the manuals as to why this resistor
is there. Why is it? To avoid ground loops?

Chris

Pardon if I was speaking too off the cuff and using language or wording that was inaccurate, misleading, or wrong. I'm a newb at this TekScope thing.

By passivation I meant the material used to fill a TO-72 can. See picture:

/g/TekScopes/photo/262237/0?p=Name,,,20,0,0,0

FWIW this is Q4402 of the 465, SN < 250K, discrete vertical amp assembly. The part number is 151-0212-00 and a Tektronix manufactured component. I searched this site and found cross references to 2N6304 and 2N5179. See:

/g/TekScopes/message/37963

Thread subject "help - transistor replacement (for tek2232,2236..)". These particular xtors are used as the first stage in both 465 and 2235/2236 vertical amps. They also happen to be the 2nd and 3rd stage of the 465 vert-amp.

Mouser (nor anyone else I found) had 2N6304, but did have 2N5179. I don't know that the 2N5179 is up to snuff for this application, but they'll do better than the 2N3904s temporarily in there now.

My 2236A uses a different part number for the first stage, but the same schematic topology. I did a cursory first effort search on those but also did not find a replacement. I need to dig deeper on that front. I'm also trying to teach myself the width, breadth, and depth of transistor characteristics so I can better judge equivalent replacements. I have a number of threads going on that front and it's just a work in progress.

Being an IC engineer I'm familiar with planar passivation. I'm not as intimate with mask design and current fabrication processes today, but I believe modern passivation layers are more complex than SiO2 and include "nitride" and/or other compounds to protect the die. Not to mention the plethora of packaging available.

I found it likely _not_ merely coincidence that this transistor has failed _and_ has some form of manufacturing defect. An engineering axiom brought to my attention some time ago is that engineers/designers/manufacturers rarely do or add anything without good reason. I doubt the "goo" is there only to secure the leads. Mind too that these particular components were manufactured by Tektronix in the late 60's or early 70's. I don't think the industry had quite settled down at that time. Wink. My use of passivation seemed an apt term. Perhaps I should have stuck with goo. Wink.

Pretty entertaining and educational project. Many thanks and kudos to Wes and friend for letting me have at it.

Dave

I've just noticed something odd about the calibrator outputs on my
535A scope and 127 plugin power supply. They both have a 0.25R
resistor in series with the calibrator socket's ground connection. The
reason I noticed is that the 127's resistor is open-circuit, so
connecting the calibrator to another piece of equipment left the
ground disconnected, with the expected symptoms.

I couldn't find any information in the manuals as to why this resistor
is there. Why is it? To avoid ground loops?

Chris

?Surface contamination is a major issue in semiconductor fabrication and use. You *must* coat the die (with something that is super-clean) or evacuate the can. In the Germanium days, the coating of choice was a thick liquid, probably a silicone.

The discovery that Silicon Dioxide made an excellent, easy-to-create passivation layer was one of the breakthroughs that allowed Silicon to eclipse Germanium.


Did I answer?


Dave Wise

________________________________
From: [email protected] <[email protected]> on behalf of Michael W. Lynch via groups.io <mlynch003@...>
Sent: Thursday, March 25, 2021 8:31 AM
To: [email protected]
Subject: Re: [TekScopes] TEK465 Horizontal trace

On Thu, Mar 25, 2021 at 07:12 AM, Raymond Domp Frank wrote:

After pulling the transistor out I found that the passivation in the can
was
only half filled.

What does that mean? I know glass passivation but "filled"?

Raymond

Add me to the list of those who are confused.

--
Michael Lynch
Dardanelle, AR

On Thu, Mar 25, 2021 at 07:12 AM, Raymond Domp Frank wrote:

After pulling the transistor out I found that the passivation in the can
was
only half filled.

What does that mean? I know glass passivation but "filled"?

Raymond

Add me to the list of those who are confused.

--
Michael Lynch
Dardanelle, AR

On Thu, Mar 25, 2021 at 02:06 PM, Tom Lee wrote:

The passivating goop that Dave is referring to was common in the
alloy-junction and mesa days

I remember the goop-filled Ge transistors, like OC-, AC- and AF-'s (I am European, so Philips, Valvo, no 2N-).
The first time I heard about oxide/glass passivation was when the term "glassivation" was used and explained. I guess it was in a TI document in the (very) late '60's.
The Dutch language doesn't produce these contractions as easily as English and German do.

Raymond

On Thu, Mar 25, 2021 at 10:11 AM, <toby@...> wrote:

That was probably about the 2N3055(A), it comes up regularly.

--Toby

OK, then I was not imagining that this discussion had occurred. I was wondering if this could be a similar situation? Your thoughts?

Thanks!

--
Michael Lynch
Dardanelle, AR

On 2021-03-25 10:48 a.m., Michael W. Lynch via groups.io wrote:

On Wed, Mar 24, 2021 at 11:01 PM, Jeff Dutky wrote:

I've been trying to find what the selection criteria were for Q1197, which is
Tek part number 151-0209-00, if I am not mistaken. ...

-- Jeff Dutky

I vaguely seem to recall a discussion from some time ago regarding a similar type of power transistor, in another instrument.. Something about epitaxial (high gain) vs hometaxial (low gain) construction with a lower gain hometaxial construction being the "Desirable" characteristic in the particular application? I just do not remember all the details. Or perhaps I am just wrong?

That was probably about the 2N3055(A), it comes up regularly.


--Toby

I see that the TEK Common Parts list calls for an HFE of 20 and the 2N3442 shows an HFE range of 12 to 72. Perhaps this memory above applies and TEK selected those parts with a fairly low HFE?

Just a thought.

On Wed, Mar 24, 2021 at 11:01 PM, Jeff Dutky wrote:

I've been trying to find what the selection criteria were for Q1197, which is
Tek part number 151-0209-00, if I am not mistaken. The service manual does say
that it is selected from 2N3442, but when I consult the Common Design Parts
Catalog I do not find 151-0209-00 listed under selected transistors. Further,
in the section that discusses (and tries to dissuade engineers from using)
selected parts it sounds like a selected part should have a part number
starting with 153- rather than 151-. It also sounds like there are a
population of 151-****-89 parts that are still considered "selected" in the
sense that while they have failed the selection criteria, they have been
checked to be free of other faults, and so are considered higher quality
parts.

Could it be that Q1197 is from the latter population of selected parts and
that the -89 suffix was not yet in use when the 454 was designed? Maybe any
old 2N3442 would suffice, so long as it was working?

-- Jeff Dutky

I vaguely seem to recall a discussion from some time ago regarding a similar type of power transistor, in another instrument.. Something about epitaxial (high gain) vs hometaxial (low gain) construction with a lower gain hometaxial construction being the "Desirable" characteristic in the particular application? I just do not remember all the details. Or perhaps I am just wrong?

I see that the TEK Common Parts list calls for an HFE of 20 and the 2N3442 shows an HFE range of 12 to 72. Perhaps this memory above applies and TEK selected those parts with a fairly low HFE?

Just a thought.
--
Michael Lynch
Dardanelle, AR

1 + -1 = 0

Unwanted noise is a side effect of amplifying a desired signal. The ratio of internal noise to desired signal is greatest at the first stage of amplification and magnified in further stages. If a portion of the signal coming from the first amplification stage is inverted and fed back to the input, it will tend to cancel the internally generated noise more so than the desired signal, improving the ratio seen by the input of the next stage.

To make it more confusing at my A1 board (version -06) jumper P600 is connected differently.
Anyway I thought to remember the same problem. I tried a 7704A with 7S12 and 7A26/7B80. With P600 in "as is" position (must be enabled) the interdot blanking pulses are always effective. The other position works fine. The same happens wit a 7854. So the problem is not restricted to the 7934.
You probably don't observe the blanking pulses when you only select Left and B. But that's because the sweep rate and dot rate rates are unrelated. Now trigger the 7Bxx externally from the 7S12 vertical output or sweep output. At 20 us/div you will recognize the between samples periods and the blanked parts therein.

Albert

I am as intrigued by Dave's comment as you are, Raymond. I have never seen a production JFET that wasn't built in a planar process. They existed, but by the time the 465 was in design, non-planar JFETs had long since died out. The passivating goop that Dave is referring to was common in the alloy-junction and mesa days (and it didn't really work well), but one of the main selling points of the planar process was its oxide passivation -- no need for the goop. There should be no goop-filled parts in a 465.

So I'm very curious!

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

One question: The caps in the grey and red rectangular boxes, I thought those
were film caps. Why would they need to be replaced? Do those have a history of
failint? I have some boards from the '60s with Wima film caps like those.
Those Wima caps are al still good.

Or did Tek use something less reliable than Wima?

Jim
Yes, they are film caps - The grey ones are Vishay rated at 440VAC, and the red ones are Wima DC.

They are all for use on ONLY the PSU block, which as we all know has the original prone-to-explode Rifa Paper caps, which are also especially under-rated for any scopes used in 230VAC areas.
Also, the PSU block has NO Wima caps factory-installed, and the kit's Wima's upgrade certain electrolytics and tantalums.

The objective is to do this job right, once only, and never have to worry about servicing it again in our lifetimes, including the 40-year-old's among us old-timers! So far, my own 2465B is now 12 years since I overhauled it, using this exact kit, and never had even a tiny hiccup.

The Wima's which Tek DID install on the other PCB's are NOT replaced.

On Thu, Mar 25, 2021 at 06:55 AM, Dave Peterson wrote:

After pulling the transistor out I found that the passivation in the can was
only half filled.

What does that mean? I know glass passivation but "filled"?

Raymond

On Thu, Mar 25, 2021 at 06:50 AM, Ozan wrote:

In this video I think I know what is happening. You have variable horizontal
knob out (time 0:13 in the video). Your 5ns B gate is 300ns wide instead of ~
130ns Raymond measured so this is supporting the theory of variable time
scale. When you switch to 10ns it is the same RC time constant as 5ns (2x is
in horizontal amp) but because variable time is disabled for B other than
1/2/5n, B-gate suddenly looks like it became shorter. If you push in the
variable time scale knob my guess is you will see 5ns width same as 10ns
width, not jumping to a smaller time. I tried it and can replicate what you
are seeing with variable time scale set.

I noticed this a few days ago, when I observed the unlocked variable timebase knob and had to fine-tune my settings in order to get exactly the screens that Ondrej showed in his video, so I wrote and suggested:

*** QUOTE ***

Gentlemen,
First of all, in order to make life as easy as possible, it would help me/us if we would "standardise" our settings:
- A-ramp at top
- A-gate below that
- B-gate below that again
- Variable timebase knob in the "calibrated" position (pushed in)
- Delay Time Position to minimum (0)
- Observation 'scope (2465B?) in non-delayed mode
- Trigger on A- gate trace

My observations match Ozan's latest ones.

** UNQUOTE **

I thought that things were made unnecessarily complex by using the delayed display on the observation 'scope and variable time base in the video.

Raymond