Re: Zener diodes on 475?


I have discovered that they are tunnel diodes (152-0386-00) and cannot be tested with a multimeter. I am wondering where I can find a circuit diagram that marks them. There are also many discrepancies between my board and the 475 or 475A schematics I have. Maybe there were modifications.

Re: Zener diodes on 475?



Those are indeed Tunnel diodes for the trigger circuit.

Michael Lynch
Dardanelle, AR

Zener diodes on 475?


I have found, a couple of short circuited zoner diodes on my 475. They are gold plated and fit into sockets on the triggrer Z axis board, both anodes to ground. They are marked GE 0386, but I don’t know their value. I am wondering if they might be tunnel diodes, although they are marked zeners on the board but I cannot find them on the 475 or 475A schematics. Does anyone have any idea what they might be?

Re: Suggestion for our group Administrator

Jared Cabot

What could be a good compromise is a 5 minute delay on the emails going out after the 'reply to group' button is clicked.
In that 5 minute window, an edit button could be available, but once 5 minutes has elapsed, the message is set in stone.

That would probably require the feature to be made available by the team though maybe?

In any case, I have no strong feelings in either direction.

Re: Suggestion for our group Administrator


My 2 cents worth: Let the the administrator choose whatever option is the easiest to manage. I am very thankful for all the effort put into keeping this group going smoothly and would not want to add additional complications. I can adapt to anything.

I try to avoid making mistakes in the first place; if a serious one creeps in, I mark the correction with an initial "Oops". If it is possible to let a poster remove one of his/her own messages from the site, we could keep bad information from cluttering up the site.

Re: Suggestion for our group Administrator


On 2021-09-12 2:04 a.m., Brian Cockburn wrote:
Could I perhaps suggest a short trial. Maybe just 2^9 hours. Then ask again to see if the "No" team might have some members change to "Oh alright then".

Mods please step in in both groups, meta thread needs to end.

Re: Suggestion for our group Administrator

John Griessen

On 9/12/21 8:28 AM, Alex wrote:
I have no desire to operate this forum through multiple never ending stream of emails when I can simply and easily do it on this simple and easy to use web interface. I know opinions vary. Perhaps I am missing some advantage, but can't imagine why
Advantages of using an email reader:
sorting emails into buckets by list name
killing messages from certain senders and with certain subject words
ease of response to individuals off list.
search through your current set of incoming emails for keywords, (and maybe dump the rest).
use threaded setting to see subject lines and decide to read some subject threads without looking at the rest.

By using a few tools as above, dealing with the volume of posts is better time management than with the web interface, and the web interface has an annoying login required every so often, but email reader has logins automated in a secure way.

John Griessen
no editing

Re: Suggestion for our group Administrator


In forums when posting, it helps me to read (and sometimes to re-read) my own message with the PREVIEW feature and that usually allows to catch any required corrections or changes before the message gets posted. But of course at times there is the inevitable small mistake that sometimes still gets through, or 5 minutes after posting I change my mind on how I wrote some part and want to try to change it to make it clearer, or update some information, etc, so I can sympathize with people wanting to have an edit feature added. Perhaps it might help a few people to share how I operate this forum.

I am writing these lines (on a laptop) while the thread is open in Firefox, which has a build in spell "check as you write" feature and will automatically highlight common spelling errors with a red underline. Of course when a change to the post ends up being needed not because of a spelling mistake but rather the way some part of the content is expressed, then spell checkers are of no use. Also most email programs have a build in spell checker that does the same (mine does), but I have no desire to operate this forum through multiple never ending stream of emails when I can simply and easily do it on this simple and easy to use web interface. I know opinions vary. Perhaps I am missing some advantage, but can't imagine why anyone, other than perhaps an admin, would want to do it the hard way by having to deal with untold number of emails just to read and follow a thread. Also not sure either why any adult, unless they are in a airport lounge waiting for their flight, would want to regularly use a phone keyboard to send sometimes lengthy forum postings. I gave up and left behind trying to type on a damn phone keypad years ago and left it to the teenagers. And no, my finger size is not the problem by a long shot. But then again, perhaps some persons just don't have any other option but to type on a "smart" phone, or even enjoy it. But for me, even if the only other option would be a basic $100 laptop, that would be a million miles ahead of typing or reading postings on a phone.

Not sure how others operate this group, but I find that receiving a single and compact email in the morning with all the latest posts of the previous day is the most convenient and efficient way as there will be one link per thread, and I can easily open any thread of interest in Firefox. Then its up to one to get to the tail end of it to see the latest post or postings, but it works for me. And all this in a single short email. If I want to save the email to preserve a link because of a specific thread of interest for future reference, my email program allows me to edit both the body and subject of inbound emails, so I can delete all the body text that is not desired around the link of interest, and then just simply change the subject to the name of the thread. I really have no need to follow any exchange live and up to the minute, I assume others need or want to, but when I am interested to keep taps on postings of an ongoing thread, I just leave it open in Firefox and set it to refresh every 30 minutes or whatever seems reasonable, and it will automatically show any new posts for the duration. And no email deluge.

Just my $0.02.

Re: TEKTRONINX P6139A shorted, metalic, Grow Metal Crystals? any definitive solution?

Roy Thistle

Hi Jeff:
Well... in his video... he cleared the short by washing out the socket on the cable where the probe tip screws in... with a brush soaked in alcohol.
Did you watch the video?
Maybe it's not a "tin whiskers" problem?
Roy Thistle

Re: Help needed bringing a 555 back to life

Morris Odell

The voltage across C640 is close enough to normal as is the parallel combination of R646/647. But something doesn't make sense. The 5651 is a voltage reference tube that should be at a constant 85-86 volts when lit. It gets its feed from the -150 line through R608 so even if it's open circuit or faulty the voltage across it can't be more negative than the -150 volt line which you say is at -148 volts. Likewise the grid of V634 is fed from a divider that has the -150 as it's most negative end and a plate of V624 as it's positive end so it can't be -153.5 volts if the -150 line is at -148. If the plate of V634 (connected to the grids of V647) really is at 0 volts then V634 will be cut off and V647 will be conducting hard, making the -150 more negative which is clearly not happening. Under these circumstances the voltage there would be slightly positive as it's pulled up by R633 but V647 could be pulling grid current and sucking it down to 0 volts. Make sure pins 3 and 6 of V647 really are at chassis potential. You need to check that what's in your 555 corresponds to the schematic.


Re: FG502 No wave


Hi Chris,

U200 Starting point around "1" on the frequency adjustment dial = +0.1V. turning the control CCW increases the voltage gradually to +9.7V. It then >jumps suddenly to +17.85V and as I turn another 2-3 sub-divisions, it jumps back to +0.1V, the starting point.

U135 Starting point around "1" on the frequency adjustment dial= +7.28V. turning the control CW increases the voltage gradually to +19.7V

U140 Starting point around "1" on the frequency adjustment dial= +6.67V. turning the control CW increases the voltage gradually to+16.43V when it
jumps suddenly to +19.1V, stays there a few sub-d-visions and jumps back to +6.67V, the starting point.

U170 Starting point around "1" on the frequency adjustment dial= +7.2V. turning the control CW increases the voltage gradually to +18.00V.

U175 Starting point around "1" on the frequency adjustment dial= -6.49V. turning the control CW increases the voltage gradually to -18.15V.

These voltages are OK. Once all the issues are fixed calibration will make them more accurate. R110 (frequency control) pot seems to not stop at the end and continue past the contacts. Probably a mechanical issue but it is not the cause of the stopped oscillations.

Oscillator could be one of several states so instead of a lengthy flowchart if you can measure few voltages we can narrow down the issue.

Setup: Turn the dial so that output (pin 6) of U135 is about +10V, pick triangle waveform, pick 10^3 range.

Measure the voltage across R140 and R175. This tells us if current sources are working.

Measure the collector voltage of Q292. In normal operation it should be a square wave with +/-5V amplitude but since your unit is not oscillating just note the voltage.

Measure the collector voltages of Q315 and Q325. This tells us if gating circuit is stopping the oscillation.

Measure base voltage of Q230A. In normal operation it should be a square wave with +0.5V/-0.6V amplitude.

Measure gate voltage of Q200. In normal operation we expect ~ +1/-1V amplitude triangle wave. This tells us how the oscillator is stuck (railed high, railed low, floating in the middle).

Measure emitter voltage of Q210. This voltage is expected to be same as gate voltage of Q200. Tells us if Q200/Q204/Q210 buffer is working.


Re: Suggestion for our group Administrator

Brian Cockburn

Could I perhaps suggest a short trial. Maybe just 2^9 hours. Then ask again to see if the "No" team might have some members change to "Oh alright then".

Re: 465M

Jim Ford

Ah, the lag; that's why I am not interested in a 2465. I had one several decades ago at work, and it drove me nuts. No, you're not ridiculously picky, unless we both are!

7000 series for me, thank you. And someday, an 11800 series.

Jim Ford

------ Original Message ------
From: "Jeff Dutky" <>
Sent: 9/9/2021 1:36:26 AM
Subject: Re: [TekScopes] 465M

Michael Lynch wrote:

> If I were going to add a 465-variant to my collection I would prefer a 475B

I am guessing that you meant a 465B?
Yes, that is what I meant. I wish that Tek had made a version of the 475 with ALT horizontal mode, but the 465B is almost close enough. The fact that you can see three simultaneous traces on a 465B also makes it interesting to me. I had kind of hoped that the 465M was more like the 465B. I had not realized that it was even more cut down for the sake of cost savings.

I guess that you can view something like the 2465 as the "B" version of the 475 or 485, both because of the 2465's other similarities to the 485 (e.g. higher bandwidth and 50 ohm inputs with overload protection), and because you get the external trigger channels that can be viewed on the display along with Ch 1 and 2. You even get other goodies that the 465B doesn't have, like readout, cursors, and (optionally) a counter/timer.

I have a 2465, which I use all the time, and really like, but I don't like that the price of all those extra goodies was that the controls became much less "direct" and more "fly-by-wire." I especially don't like the position controls that are both laggy, and have a tendency to get out of sync with the on-screen position (they could have remedied that by using knobs that didn't have an indicator, and pots that didn't have a stop, as they did with the cursor controls).

I am ridiculously picky about these things.

-- Jeff Dutky

Re: Help needed bringing a 555 back to life

Selinica Harbinger

C640 has 272V across it in mine. The 5651 has -172V across it. The R646/647 pair reads as 498.8Ohm measuring from node to node. I didn't desolder them to check as maybe I'm just blind but they were hard to locate. The plate voltage for V634 was 0V and the grid was -153.5
I can get the -150V adjustment wiper to -148V at best.
Tube were given a check over initially and the weak ones swapped. The indicator cable was checked for continuity and to make sure there were no shorts between lines that should not be there.

I did note a small scorch mark under L790 where the resistor is and the diodes D642, 702, 732, and 672 all seem to have been replaced by a prior owner. They do not match the look of the D762 set nor the manual images or the pictures of other power supply units.
That's just a visual inspection though, all parts tested fine with diode tests and the resistor checked out.

Re: Repair of a 7S14

Ed Breya

Yes, the PV MOSFET drivers should work great as current sources, with plenty of voltage - you would just have to shunt regulate them with LEDs. Only a single PV would be needed for each channel. Don't bother with regular transistor optocouplers. You'd need about five per channel to get enough total voltage, making the total parasitic capacitance too large - I've tried it. The transistor optocouplers do however, have significant output current in the tens of uA, but only one Si junction voltage, so you need a bunch to make decent voltage. You take the output from the B-C junction, and run the LED as high as possible. This means you have to use the big six pin type to access the base. The four pin ones only connect the C and E. These generators can be quite useful in certain situations.

My most recent use of this kind of deal was in the Keithley 417 electrometer upgrade project, where I made an adjustable, bipolar voltage source that floats on the output signal, in series with the very large feedback resistors, in order to null out the input bias current. The optocoupler circuit was by far the simplest method.


Re: 7T11 diode tunnel destroyed connecting a 15pF 1:10 probe?



Re: "mottled effect" on anodized front panel

Roy Thistle

On Sat, Sep 11, 2021 at 02:38 AM, Sparky99 wrote:

on closer inspection the scope has a slightly mottled effect on the anodized
front panel.
I'm sure I've seen it too. A kind of mild staining? ... in some areas.
It could be, as suggested, and exposure to uv... but, that usually happens when the anodized part is colored. I don't think there is any coloring in these front panels.
The usual thing to do when anodizing aluminium is to seal the anodized part.
It could be that the particular batch that these panels came from did not get sealed properly. Then they would naturally get contaminated, in some areas, over time.
Perhaps these came from the factory with the defect(s) you observed?
It's also possible the scope had 'grime' on the front panel for a long time... that and perhaps a humid environment... that might have engendered an electro-chemically induced etch in some areas.
If you've tried a mild and neutral detergent (you say "soapy water") and it hasn't cleaned up... then anything harsher isn't recommended.
Anodizing... when done correctly, is supposed to to last for a long time. But, these panels have been around a long time already.
Perhaps one will have to live with it? ... or risk doing more damage.

Roy Thistle

Re: TEKTRONINX P6139A shorted, metalic, Grow Metal Crystals? any definitive solution?



According to the TekWiki entry on the P6139 the cables have "a whisker- or dendrite-growth problem," the fix for which is to replace the cable. There is a temporary fix that involves running current through the BNC connector to burn away the whiskers, but it is only a temporary fix. I have avoided buying cheap P6139s on eBay for exactly this reason.

The literature on tin whiskers is fascinating and bizarre.

-- Jeff Dutky

Re: Repair of a 7S14



Well, first, the original discussions (blog posts?) by Ed did talk about using an opto-isolator to generate the bias voltage. If I recall the post correctly, the only reason he went with LEDs was because he was pulling things from his junk box. Second, the PVI5080 would require voltage regulators to bring the 5V output down to the 1.35V range matching the output of the mercury cells. Maybe other opto-isolators would have output voltages closer to the target voltage? Third, I was captivated by the fact that you could turn an LED into a voltage source (not exactly DIY self-satisfaction, but satisfying curiosity and entertainment), and am enjoying the experimentation. Finally, while I was not unaware of the existence of opto-isolators, I was not familiar with all of their properties (despite reading Ed's account).

I actually have a couple tubes of old opto-isolators that may be suitable ("old" as in "maybe older than the 7S14 I'm trying to fix"). I should see what their specs are.

-- Jeff Dutky

Re: Suggestion for our group Administrator


I would like to second that, for my two reasons:

- Never change a running system for trifles
- Errors, typos and such are no big deal, science has ever been able to overcome

For me fake news (not in this group but in general) are much worse a problem nowadays

Regards, Joe

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