Re: Grid Bias Adjustment on 475A
Happy new year guys!
C 1374 is a possible culprit. You can always replace it and give it a try. If not, you could solder a couple of leads to the viper and the 50 volt ends of the pot and bring them away from the HV area to test. Since one end of the pot is grounded, you should be able to easily check the other end for 50 volts. If that is OK, then see if the viper has a voltage that is somewhere in between 0-50 volts. The issue is that it might be close to one end and the best test is to observe that lead while the power is on and turning it slightly with a plastic screw driver. If you decide to do that, make sure to mark the initial position as it is.
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Re: Wanted: TDS3000 hub assy. for handle
If you don't find a used one, they are still available from Tek @ about $35.
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Re: Rescuing 500s from tube snatchers/scavengers - how much is it worth
My 561 has a bad HV XFMR, will cryo tubes and special audio cables fix that?
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Re: Grid Bias Adjustment on 475A
R1375 is deep under the HV shield, but that's hardly my issue (I've been operating the scope without an HV shield for weeks). The real problem is that the grid bias pot is snuggled up close to what I believe to be the circuitry that generates the KV potentials, and I'm not too happy about poking around in there with a test lead (much less a scope probe) with the power on. I can hook the lead of a flying capacitor in the grid bias circuit, but it's separated from the center tap of the pot by another resistor (still not a huge problem, but it just adds to my analytical burden). The layout for the 465 looks a little different than the 475. It looks like the corresponding pot on the 465 is called R1480 "CRT BIAS" and is much further removed from the HV section than on the 475.
I am worried about getting a good reading in circuit, but am I wrong in thinking that any path from either ground or the +50 V rail should be fairly high impedance (like Megohms)?
Now that you mention it I notice that there's another component that could be dragging on the output of the grid bias pot, if it has failed that is: C1374 is a 1uF decoupling cap of almost identical make to the one that failed on my father's 475. If that were conducting significantly it would surely mess up the grid bias voltage.
-- Jeff Dutky.
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Re: Rescuing 500s from tube snatchers/scavengers - how much is it worth
I tried cryogenically treating the tubes in a 561A You sure that wasn't a 570 Characteristic Curve Tracer Now all my sine waves look like so...
I'm not sure if I want to calibrate it back out..... Dude, I'm thinkin' it's seriously -in- cal' .... :-) Bill
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Ok, heads up, time to go re-download the files if you already downloaded them.
I found one transistor backwards (So test 1 wasn't working right), this has been rectified and the unit is now 100% certified as working by me (but that doesn't mean much... hahaha :D )
The aluminium plate behind the plastic plate can be easily constructed from some 1mm thin aluminium, 61mm x 120mm with 3.5mm holes in each corner (Measure against a plastic face plate to get their positions exact).
As Larry said, shielding is not an issue here so if a 3D printed part for the front panel was to be made, with the thickness of the now absent aluminium plate integrated into the 3D print instead, it might just be ok if you use a high infill percentage.
I've added add a STEP and STL file to to the files that will be able to be used for this purpose if someone wants to try it.
As for whether this was available for purchase from Tek as a completed product, I have a feeling this may have originally been a side project or similarby Warren Collier at Tek, and it must have worked well enough that the construction notes were released as a DIY type of thing.
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
On Thu, Dec 31, 2020 at 05:50 PM, Jared Cabot wrote:
Wow, I didn't expect such a big response
Thank you for the project. But, I don't get it? I know there is a TekWiki page for this thing... but, was this ever produced and sold by Tektronix? (It seems like something they might have used in production, and that someone? decided to release as a project?) I did check the 1977 catalogue... didn't see it in there?
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Re: Tek 2465b two probes showing slightly different voltages and phases
No, apparently, the nanosecond is out of favor this year (as of about 42 minutes ago) and the arcsecond is in. Go figure.
DaveD
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On Dec 31, 2020, at 19:37, Tom Lee <tomlee@...> wrote:
A nanosecond just isn't what it used to be... :)
--Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 12/31/2020 16:27, Tom Gardner wrote:
On 31/12/20 21:53, Tom Lee wrote:
Enjoy that scope, Mark -- it's an amazing instrument. Consider that it is so capable that the finite speed of light was the root cause of your delay problem! Nice to own a scope where you start complaining about light being too slow...
Here's a nice video of (Rear Admiral) Grace Hopper demonstrating the "size" of 1ns in vacuo: a piece of wire 11.8in long. In a cable it will be shorter, due to the reduced speed of light.
The 1972 portable Tek 1502 TDR is capable of resolving discontinuities 140ps apart, i.e. ~1.2in in a cable.
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Re: Grid Bias Adjustment on 475A
Trying to find R1375 & associated components on your earlier pictures, but I think from looking at my 465 that they're just out of frame.
Also using my 465 as proxy, it looks like the zener diode and 10k resistor node (don't have your schematics at hand for #'s) are accessible. I'm not advocating, and I wouldn't blame anyone for not being comfortable operating their scope with the shield off, but can you get a measurement off this output of the R1375 pot? Looks like it'd be possible to get a 10x scope probe on one of the leads of the cap maybe? Reassemble the shield and see if the value responds to turning the pot - again with the shield on. And this all depends on the 475A board layout, accessibility, clearance for the probe with shield, etc.
I'd be wary of trying to get a good R value in situ with the 50v supply being connected to the regulator divider feedback network.
Dave
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Non-working TM500 modules appear on eBay from time to time at fair price and include top,? bottom and side panels and the all-important latch-release pull-tab. Shielding is not important for this tester and 3D printed parts might be adequate if made strong enough.LarrySent via the Samsung Galaxy S10
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-------- Original message --------From: Jeff Dutky <jeff.dutky@...> Date: 12/31/20 8:43 PM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] I built a TM500 mainframe tester, and updated the design. Someone might find this useful? Does anybody now if the aluminum plates are required? Would plastic plates (3D printed or otherwise fabricated) work just as well?My stable of TM500 modules is already pretty thin, and I don't have any unrepairable units lying about.-- Jeff Dutky
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
In my experience, the 3D printed plastic frame needs a thin gauge aluminum backing to give it rigidity.? If you had any machine shop capability (such as a decent drill press), you could make your own plates.? The idea of a bare PC board is not at all a bad one, your choice of whatever the board solder mask is.? However, I've seen no silver boards at all.? I'm going to experiment with a 3D printed overlay, possibly black, possibly blue, but it could be the same gray as the normal plastic backing.? YMMV on this.
The standard construction on the modules seems to be a thin aluminum plate, a plastic backing plate (screws go through these two), and a front plate that's silk screened and held on by control knobs.? Makes a clean appearance.? It's possible to do a transparency, either laser or inkjet, and perhaps put a thin layer of transparent plastic over it, that gives you photo art.? The advantage of an inexpensive board would be that all the machining is done for you.
Harvey
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On 12/31/2020 11:43 PM, Jeff Dutky wrote: Does anybody now if the aluminum plates are required? Would plastic plates (3D printed or otherwise fabricated) work just as well?
My stable of TM500 modules is already pretty thin, and I don't have any unrepairable units lying about.
-- Jeff Dutky
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Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603
Wow.. I just checked my 40 + year stash of normally useless crystals, and found
52.500000 CR-55A/U. Probably a 3d OT, but the spec should tell. HC-18 with
the hard pins, not flying leads. Yours for post and a coffee.
JimMc
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-----Original Message----- From: "Tom Lee" <tomlee@...> Sent: Thursday, December 31, 2020 7:20pm To: [email protected]Subject: Re: [TekScopes] Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603 Yes, finding oddball crystals is a challenge. I very much doubt that you will find 52.5 (or 55, for that matter) MHz crystals as standard stock items, so your choices are limited. If you can't find them as off-the-shelf or surplus items from the usual sources (including ebay), you'll have to have them made. So, your next question would be: Who makes custom crystals? The number of good answers is unfortunately diminishing with time, as vendors disappear. About the best recent discussion I've seen is a couple of years old: Scroll down near the bottom of the first page. A poster "drussell" offers a comprehensive list of potential vendors. Warning: Custom crystals tend to be rather expensive. You may spend as much or more just for the crystal than for a nanoVNA. :) In discussions with potential vendors, let them know that you would be happy with a third-overtone crystal, if they ask. Fundamental-mode crystals for that frequency range exist, but are incredibly expensive. Plus, the TR50x gens already use third-overtone crystals. No need to pay a surcharge on top of a surcharge. Good luck! -- Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 12/31/2020 12:16, Attilio wrote: Hi everybody,
where can i find the 52.5 MHz crystal? It is hard to find!
Thanks and happy new year
Attilio
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Does anybody now if the aluminum plates are required? Would plastic plates (3D printed or otherwise fabricated) work just as well?
My stable of TM500 modules is already pretty thin, and I don't have any unrepairable units lying about.
-- Jeff Dutky
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Re: Grid Bias Adjustment on 475A
Okay, I've examined R1375 (with the power off, and I'm not sure where to probe for anything other than that center tap on the pot, so I can't really answer whether it's seeing the full +50 V at one of the outer terminals) but the pot seems (to my uneducated eye) to be acting strangely. I was able to find a pad that is connected to the center tap of the pot, so I measured its resistance between center tap and ground, and between center tap and the +50 V rail, as I turn the pot through its range. It starts a effectively zero ohms (0.001 K ohm), goes up to about 6 K ohms, then drops down again to around 2 K ohms. The schematic says this is a 25 K ohm pot, so shouldn't I expect it to go from 0 to 25 K ohms?
If it turns out that the pot is dead, I guess that's good, but I don't relish the idea of removing the main interface board to unsolder and replace this trim pot.
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
I ordered my rotary switch from Digikey, looks like there are 100 in stock with a little bit of a price break for multiple purchases.
Might be worth looking around for cheaper prices, I didn't ask the manufacturer for direct pricing, but that might be worth the time spent to send an email to see if cheaper pricing is a possibility.
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Six list members have said they want to participate in a group buy of these board sets. Those are:
ML
PA
SM
DC
HB
GL
I've asked Jared for clarification on some points and for help ensuring the order is placed correctly. I'm waiting to hear from him.
I'm inclined to place the order with the same board house Jared used. I'm not willing to go into a lot of competitive bidding on board cost! I don't know the cost of a set of four boards but it can't be that much...
I live in Southern California and am retired so I can manage a group buy, with reimbursement via PayPal Friends and Family. There is a very special PWB-mount rotary switch required; I may buy a lot of those to ensure availability so that would likely be part of the board set purchase. Be aware this is a $25 switch! Many of us have other standard parts available so I'm not enthusiastic about buying other parts.
So, think about really wanting to build one of these testers and let's see if we can make a group purchase work.
I'm currently building a GPSDO into a TM500 proto module. But, any non-working TM module can be bought and stripped to provide the chassis structure for this tester. The PWB set makes is easy...
I welcome your constructive comments. Note the cost of the rotary switch stated above.
Larry
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On 12/31/2020 3:12 PM, Larry McDavid wrote: Anyone interested in buying sets of boards to share?
Larry
On 12/31/2020 11:27 AM, Jared Cabot via groups.io wrote:
Hi all,
I have been accumulating TM500 modules and mainframes for a little while, so I recently finished building an 067-1201-99 TM500 mainframe tester from the Tek construction notes floating around.
I updated the design somewhat and designed it for simplified construction (Not a single wire to strip and solder!) and I thought someone here might be interested in taking a look or even building one themselves.
Here's a link to the youtube video:
And here's a link to the google drive with all the gerbers and schematics and stuff. I went so far as to rewrite the manual with the alterations and corrections included.
Direct link to the new manual:
Let me know what you think, and let me know if you see any errors that need correcting. :)
Regards
Jared.
--
Best wishes,
Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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Re: Grid Bias Adjustment on 475A
I have not examined the grid bias trim pot (R1375) yet, so I don't know what voltages it sees. Like I said, if it turns out that the trim pot has drifted out of spec that would explain a lot of what I'm seeing. I'll see what I can measure straight away.
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What do you mean by chip? 74LS logic and SRAMS can be tested with the TL866 II device programmer.
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Greetings,
Allow me to seek some owner/user comments as well as alternate suggestions.
I am considering acquiring an IC tester/identifier instrument. Currently, on-line I have found a very limited selection - actually just one unit - a Chinese built YBD868.
I have been unable to find any useful information regarding this thing. The very few on-line videos are rather worthless. They are either void of any operational demonstrations or show the unit as completely unresponsive.
Does anyone have personal experience with this unit and if ¡°yes¡± I would be very grateful for an accurate assessment.
Additionally, if there are other IC test and identification units available, which I have simply not discovered, I would greatly appreciate recommendations.
I wish all of us a much better 2021 than this year has been.
Wherever in the world you might live I hope 2021 becomes you best year thus far with many fantastic years to follow.
Regards and best wishes!
Ken
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Re: Grid Bias Adjustment on 475A
Sorry! that should be 50 volts. Not 150 volts!
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Bill Perkins
Jared Cabot
Dave Peterson