Re: Rescuing 500s from tube snatchers/scavengers - how much is it worth
No but it will sound fantastic, especially when you use oxygen free Tektronix Gold Plated Probes...
Harvey
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On 1/1/2021 2:04 AM, Bruce Atwood wrote: My 561 has a bad HV XFMR, will cryo tubes and special audio cables fix that?
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I think the best compromise might be the 3 pole midget twistlock from Hubbell, as it will give me a grounded connection, and the modification will be the lest conspicuous: slightly enlarging round holes with a step-bit, no adapter plates, and no collisions with the outer steel shell.
Thanks y'all!
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When I came across this problem (and after an unsuccessful search for my genuine ancient line cord), I took one of those rubbery 3-prong-to-2 prong adapters and, with a sharp knife, cut off the female grounding socket (along with enough of the surrounding rubber to allow insertion into the instrument. This allowed me to attach a normal 3-wire cord.
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Re: Grid Bias Adjustment on 475A
Yes, C1374 is in a good place to explain a lot of what you're seeing. But schematics aren't board layout, and the TekWiki links for 475A don't seem to have the board layouts. So I don't know how accessible these components are. I was hoping you might be able to use the hook clip of a 10x probe to hook on that cap lead, power up, and adjust the grid bias just to see if it is adjusting that voltage up and down. And by how much. If you get to that point record the max, min, and how linear it is. Then you can see if those values make sense relative to the schematic. The online schematic has some voltages annotated, but doesn't seem to indicate exactly which nodes (+107 ?).
Looking at the 50v PS circuit there's an adjustable voltage divider that feeds back to the regulator "-" input. The online schematics are difficult to make out values, but even high k Rs in parallel are going to add to a much lower resistance (1/Rt = 1/R1 + 1/R2 + 1/Rn ...). There are also several PN junctions along the way that an ohm meter may well forward bias and contribute to "false" low R values while powered off and in situ. Testing for a dead short or complete open is one thing, but beyond that I wouldn't put too much stock in such a measurement. That's my personal take/preference/opinion. FWIW, YMMV, ... And there's no guarantee that the +50v at the grid bias is direct connected to the PS output (but it does say it goes to sheet 12).
Dave
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On Thursday, December 31, 2020, 11:01:00 PM PST, Jeff Dutky <jeff.dutky@...> wrote:
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
My 561 has a bad HV XFMR, will cryo tubes and special audio cables fix that? Probably not. Posting for a friend. :-) HAPPY NEW YEAR to everyone Bill
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An IEC would definitely need an adaptor plate. The less common type with mounting holes above and below rather than out to the sides might be a better fit.
The other type I've used (again this betrays my background in broadcast kit) is XLR-LNE. I think this type was only used in the UK, by the BBC and ITV companies. They are no longer made and go for too much money secondhand. Inevtiably I have a stock of them:)
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Thanks Bruce - 'General Electric' extension cords is giving some good hits. I guess these weren't grounded via their AC socket?
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no ground on the ones I serviced, I changed all to 3 pin IEC ( they are/were on other non TEK equipment) as it was required for safety...IMO was not needed but ya do as ordered. above my pay grade.
¸é±ð²Ô¨¦±ð
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On 1/1/21 9:09 AM, Paul wrote: Does anyone know of a source for the cable-end receptacle that mates with the plug shown in this photo
The inside is metal, and I wonder if the original line cord had a metal ground ring that mated with it, like some of the larger twist-lock connectors do.
In lieu of finding the receptacle, I thought I'd replace it with the early hubbell 'midget' (pre NEMA) twist-lock connectors, but even those are too large for this hole, and I'd love not have to modify the chassis. The screw spacing is 1 1/2", and the chassis opening is 1 1/8"
thanks,
Paul
.
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Thanks!
An IEC socket /almost/ fits, but would require a little bit of filing, and maybe a plate to fill in the remaining gaps.
I'll take a look at the EP - I think I remember seeing them on consoles before. A similar approach I was considering was Neutrik's powercon, which would probably require about as much filing / drilling / bodging as either the EP or IEC cables.
The closest fit is the 2 pin hubbell midget, but that's non-grounded.
cheers,
Paul
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The cable female connector was made by several manufacturers, most I have seen were General Electric. I have never seen one with a grounding contact. You can also search for an older extension cord that has two outlets on the sides of and one on the end of the head. Find the ones molded of soft plastic rather than bakelite, and carefully carve or grind off the edges to allow it to go into the connector on the scope. Those with outlet slots on the sides of the head can not be used. Many older General Electric extension cords will plug into the connector without any alterations. Many older 3 wire ground adapters from appliances and power tools will fit into the connector on the scope and then allow you to use almost any extension cord.
Bruce Gentry, KA2IVY
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On 1/1/21 12:09, Paul wrote: Does anyone know of a source for the cable-end receptacle that mates with the plug shown in this photo
The inside is metal, and I wonder if the original line cord had a metal ground ring that mated with it, like some of the larger twist-lock connectors do.
In lieu of finding the receptacle, I thought I'd replace it with the early hubbell 'midget' (pre NEMA) twist-lock connectors, but even those are too large for this hole, and I'd love not have to modify the chassis. The screw spacing is 1 1/2", and the chassis opening is 1 1/8"
thanks,
Paul
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Here in the UK (where NEMA connectors of any type aren't really used at all) I've seen Tek scopes that have been retroftted with EP4 power inlets. Coming from a broadcasting background I have plenty of these around though they are still available new, albeit specified for loudspeaker connection, not mains.
Nice, solid, rugged connectors. They look good too, especially the older types. It doesn't help that there are 2 different wiring conventions which has caused endless grief to many broadcasting engineers. In the USA, I don't know if they are found at all. Vintage Marconi broadcast studio kit may well have used them, even in the USA.
Another approach is less good looking but inexpensive and effective. The very common IEC C13/C14 mains inlets can be fitted by using an adaptor plate. I don't think any drilling of the original would be needed though would need to check exact dimensions.
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Does anyone know of a source for the cable-end receptacle that mates with the plug shown in this photo
The inside is metal, and I wonder if the original line cord had a metal ground ring that mated with it, like some of the larger twist-lock connectors do.
In lieu of finding the receptacle, I thought I'd replace it with the early hubbell 'midget' (pre NEMA) twist-lock connectors, but even those are too large for this hole, and I'd love not have to modify the chassis. The screw spacing is 1 1/2", and the chassis opening is 1 1/8"
thanks,
Paul
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Re: Grid Bias Adjustment on 475A
Happy New Year to all!
Resolve the condition and function of R1375 before you move on. What you describe above sounds suspicious to me.
After that, there are some other component to check as well.
Check VR1374 which is the 82V Zener, CR1373 and CR1371 (both 175V, 100mA fast switching diodes). These are well known to fail and cause extreme brightness, I suppose it would be possible for them to fail some other manner and cause a "dim" display as well?
C1373 is another known problem area.
Good Luck!
--
Michael Lynch
Dardanelle, AR
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Crystals - was(Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603)
Hello,
these people might be useful:
www.krystaly.cz/en/Products/Crystals
No affilation. But I speak a few words of Slovak and are in the region...so if I can help, I will in the frame of my possibilities.
With compliments for 2021
Tam
--
With best regards
Tam HANNA
Enjoy electronics? Join 15k7 other followers by visiting the Crazy Electronics Lab at
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Re: Tek 2465b two probes showing slightly different voltages and phases
One thing my engineer buddy did in the lab we used was to look at the
¡°speed of light¡±. He took a reel of coax we had gotten to run some Ethernet
links. This was before twisted pair took over from coax for Ethernet. He
connected a pulse generator to one end of the cable on the reel and to the
input of a scope (I think it was one of the Tek scopes I had in the lab,
likely the 547). The other end of the cable also went to the input. He set
the pulse rep rate so that the pulse from the beginning of the cable and
that from the end would not be confused by a high rep rate. With a fast
sweep speed, we could see the spacing between the two pulses and measure
the time difference. His question to me when I walked into the lab that day
- ¡°Want to see the speed of light?¡±
Steve H.
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On Thu, 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: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
On Thu, Dec 31, 2020 at 10:28 PM, Larry McDavid wrote:
I welcome your constructive comments. Note the cost of the rotary switch
stated above.
Larry, I think this approach makes sense. It will not be the ¡°cheap¡± way to make this happen, but it will likely produce the best results. As I had already stated, I would be up to helping out with distribution, payments or any other facet of this project. The prices of the switch and boards would not be a problem for me. As long as the cost of boards was not in hundreds of $. Please feel free to reach out if I may be of assistance. Thanks for sort of spearheading this project. Sincerely, -- Michael Lynch Dardanelle, AR
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Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603
Thanks Tom,
yes the difficulty to find these crystals is high, but Jim has one and hopefully I can have it.
-- Cheers
Attilio
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Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603
Wow Jim,
I am in Italy, if you give me your bank details and the amount I have to pay for the crystal and the shipping costs, I will make you an international bank transfer.
Thanks
-- Cheers
Attilio
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Hi Jared,
Very nice implementation of this Power Supply Tester. Hat off.
By the way around April this year a nice 067-1201-99 was sold for USD 148.95 (BIN and eBay) and its TM5000 counterpart (067-0995-99) sold in October this year for USD 349.99 (also BIN and eBay).
May I suggest the 067-0938-00 (Notch FIlter) as a new Project. Scarce and pricey. Last one sold for USD 349.95 (BIN and eBay).
Greetings,
Egge Siert
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Re: Grid Bias Adjustment on 475A
LOL, I think you mean "wiper", not "viper"!? A viper is a kind of poisonous snake!? Such is the confused but fascinating mess that is the English language.? ?Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: "adesilva_1999 via groups.io" <adesilva_1999@...> Date: 1/1/21 1:30 AM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] 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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Dave Peterson
Bill Perkins
ppppenguin
Michael W. Lynch
Mlynch001
Attilio