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Re: Time Mark generator
Craig Sawyers
Why such concern about accuracy? Even the crappiest crystal oscYeah, I know - you can only pull a crystal oscillator a tiny amount using the parallel tuning capacitor. I just have this thing about getting things adjusted accurately, and at least this gets me a bang-on accurate counter to boot *very* easily. Craig |
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Re: Time Mark generator
Don Black
Hello Craig,
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If you can measure the colour oscillator frequency of a colour TV while receiving a transmission it will be 4433618.75 Hz., use that to check the frequency meter. The standard used to be +/- 5 Hz. but if you check with the BBC I think they use an atomic standatd now and is extremely accurate (even 5 Hz. is only 1 part per million). In the US the frequency is 3.579545 MHz. A very Merry Christmas and Happy New Year to all. I hope there's (another) Tektronix in your future. Cheers, Don Black. Craig Sawyers wrote: Hi list |
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Time Mark generator
Craig Sawyers
Hi list
One of the problems with living in the UK is that we are in the wilderness for Tek gear. You only have to look at eBay UK and US and compare the two to get the drift! Faced with not being able to get a hold of a time mark generator on my side of the pond (and since shipping costs for bulky gear from the US are prohibitive), I tried to think of a way of generating accurate time marks so I could calibrate my 545A and 7603/7B53A. Now I have a counter/timer (HP 5328A - cost me all of ???22UK), whose calibration accuracy is unknown, and I also have a signal generator whose calibration is unknown. However, if the 5328A's calibration was on the button, I would have a traceable method of generating time marks up to at least 100MHz (<10ns spacing). So what I have done is build a simple tuned RF receiver, made from a high-Q honeycomb coil (built according to ). This measured 350uH on my bridge. I then resonated it at 60kHz with two 10nF capacitors in parallel and connected it in differential mode to my 7A22. Why 60kHz? Well there is a time code transmission in the UK on 60kHz, traceable to the NPL (equivalent to the NBS in the US) to an accuracy of 1 part in 10^11 (or 10 cycles at 60kHz per year). Much to my delight, the signal from such a rudimentary arrangement was 500uV, just using the coil as the antenna (and with the hf and lf filters on the 7A22 set correctly for the frequency to reduce noise). An alternative, not yet tried, is to use the Radio 4 long-wave transmission at 180kHz (UK of course). This is Caesium clock referenced at 180kHz, and is again set to an accuracy of better than 1 part in 10^11. Quite something for a broadcast radio station! I now need an easy op-amp based high-Q filter tuned to 60kHz (over the holiday break) to reduce noise and boost the signal by a factor of 100 or so. Then I have an absolute method of checking the calibration of my timer. Now by tuning my signal generator to a particular frequency as registered by the now-calibrated timer, I can generate time marks of any period for calibrating my 'scopes! I'll let you know how I get on.... Craig |
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Re: Capacitance standardizers
Craig Sawyers
The reason I am ignorant of the "inductance standardizer" is thatHi Stan If for some reason the 300uH has been tinkered with, I guess the other way to do this *without* using the standardizer (which requires a 130LC in *known* calibration) is to deliberately resonate the inductor in the S-30 with a value of capacitor large enough to swamp strays in the wiring and winding capacitance in the inductor - say 10nF. That should resonate at 92kHz with a 300uH coil (even if the coil has a resistance of 1 ohm, the Q will still be 27). So equipped with a signal generator, and ideally a counter/timer to verify the frequency if should be possible to set the coil absolutely without relying on transferring its value from another 130LC. Craig |
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Re: Tek History book
Stan or Patricia Griffiths
The Book David Wise is referring to regarding the 545A is called "Typical
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Oscilloscope Circuitry" copyright 1961 by Tektronix, Inc. It is hardcover and carries the Tek part number 070-253 (under the old part numbering system). No author is credited. I don't know where any copies of this book are available at this time. Stan w7ni@... David Wise wrote: From: Dave Ashby [mailto:dashby@...]Thanks for the pointers, Dave! If I can find these, theyWaiting for "Case Histories in the Evolution of Scope Design"I'd be interested too. But in the meantime, there are some |
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Re: Capacitance standardizers
Stan or Patricia Griffiths
Hi Craig,
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The reason I am ignorant of the "inductance standardizer" is that I have never wanted to calibrate an S-30. I have just used them as they were and trusted that the 300 uH position on the switch was still OK. So far, so good . . . Stan w7ni@... Craig Sawyers wrote: All 130LC manuals that I have ever seen talk a lot about usingHi Stan and Miroslav |
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Re: Info on Tek 2235 , P6120, assorted questions...
Stan or Patricia Griffiths
Hello Joseph,
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I don't have anymore copies of the Tek First 40 Years book available for sale at this time. I find them around here in estate sales occasionally and put them on eBay when I get spares. Keep searching eBay and you will probably find one. Stan w7ni@... Joseph Orgnero wrote: Hello stan, |
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Re: Tektronix 545B (V)
Craig Sawyers
Even if you don't have a manual or a cap tester, you canYeah - that was my next line of advice. I'd run it the other way though; assume the cap is good, and then calculate the current from the ripple. The 6080's are good for 100mA per section - so does the ripple indicate significantly *more* than 200mA? If it does, then the capacitor is much less than its correct value, and is probably shot. Craig |
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Re: Tektronix 545B (V)
Aargh, remind me to read the whole thread next time.
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Dave Wise -----Original Message----- |
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Re: Tektronix 545B (V)
Craig Sawyers [mailto:c.sawyers@...],
answering Jose Gavila: <snip> I'm looking at the schematic of the 545A, and I suspect thatI don't think that trouble in those resistors could account for a ripple. IIRC the purpose of the 82K is to prevent some cap (maybe this one) from getting reverse voltage during warmup. The 10's are there mostly for troubleshooting. You measure across them to calculate current. Even if you don't have a manual or a cap tester, you can find out if the cap is ok. Measure the current as I mentioned above. The formula for current in a cap is I = C * dV/dT . Estimate dV/dT from your scope trace. Plug in I and dV/dT. Does C come out near the printed value? To get in deeper, you really need a manual. It tells what I should read, and it might even say how much ripple is acceptable. In any case, how's the +350 line? If it's smooth over the specified range of line voltage, you're ok. Regards, Dave Wise |
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Re: Tek History book
From: Dave Ashby [mailto:dashby@...]Thanks for the pointers, Dave! If I can find these, theyWaiting for "Case Histories in the Evolution of Scope Design"I'd be interested too. But in the meantime, there are some ought to get me bouncing in my seat :-) Actually, there is something out there that's close to an engineering analysis, but it mostly covers one model (the 545), so there's little evolutionary material. Sorry, I forget the title (it contains "Oscilloscope" of course), but it was published by Tektronix, and the public library in my city (Portland Oregon) has a copy. Some of the Tek "Concepts" books probably have stuff along these lines too, but I haven't had a chance to find and read them. By the way, I hope you all understand that "Case Histories..." is a fictitious title. I made it up. It doesn't exist; I just wish it did. It would be a companion volume to the content of this list :-) Regards, Dave Wise |
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Re: Tektronix 545B (V)
JOSE V. GAVILA (EB5AGV/EC5AAU)
Hello!
Thanks to both of you... but my message was from September, I think, and the oscilloscope was fixed back then ;-) It was a capacitor, as you suggest. Merry Christmas! JOSE ---------------------------------------------------------------------- 73 EB5AGV / EC5AAU - JOSE V. GAVILA La Canyada - Valencia (SPAIN) EB5AGV Vintage Radio Site: European Boatanchors List: |
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Re: Tektronix 545B (V)
Craig Sawyers
Snips:
Looks like a problem with the power supply filter capacitor. I'm looking at the schematic of the 545A, and I suspect that the 545B hasProblem has been traced to the +350VDC supply, which has, underload, alarge ripple (before the main relay actuates, ripple is lotslower). Thisoscillogram (sorry for the bad focusing of my picture) shows the ACvoltagejust after the rectifying diodes of the 350VDC supply (so it is NOTtheregulated voltage): the same 350V supply. The (silicon) bridge rectifier feeds the 125uF reservoir capacitor through two ten-ohm 1W resistors in parallel. It also has an 82k resistor in parallel. So check that the 10-ohm resistors are present and measure correctly, and the same with the 82k. Are you working from a schematic, BTW, or diagnosing blind? Craig |
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Re: Tek History book
Dave Ashby
Hello David,
Waiting for "Case Histories in the Evolution of Scope Design"I'd be interested too. But in the meantime, there are some interesting chapters in a couple of books edited by Jim Williams: 'Analog Circuit Design : Art, Science and Personalities' and 'The Art and Science of Analog Circuit Design'. There is a chapter by John Addis on the history of vertical amplifier design, another by Carl Nelson on T coil peaking, and another chapter by a Hewlett Packard engineer (whose name I can't remember) on the attenuator / front end design for a vertical input channel on an HP DSO. Apart from the 'scope related stuff, these books are a great read on analog design in general. But perhaps you've already got them . . . Regards, David Ashby |
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Re: Capacitance standardizers
Craig Sawyers
All 130LC manuals that I have ever seen talk a lot about usingHi Stan and Miroslav I have a pdf of the 130LC manual which gives instructions on how to make the "inductance standardizer". This is used to calibrate the 300uH range of the S-30 transfer standard. It says that calibration of the 300uH range cannot be easily done, because you can't transfer a 300uH standard from a bridge (due to stray capacitance effects upsetting the bridge). So the inductance standardizer is used; this has a fixed inductor in the range 100-400uH, a capacitor (4310pF +/-2%), a resistor (7.5 ohms +/- 2%) and a switch. It is used with a S-30 and a *known* standard 130 to set up the tuning slug in the S-30. The manual seems to be post '62. If you'd like a copy of the pdf (3.9MB), mail me off-list. Craig |
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Classic 'Scope book
Dave Ashby
Hello Stan,
I am the guy who wrote, "OSCILLOSCOPES--Selecting and Restoring aClassic". > I still have a few copies left for $24.95 I'm interested in getting a copy of your book. How much would it be including shipping to the U.K? I'd probably send an international postal money order in the new year (after I get back from a couple of weeks break). Thanks in advance, David Ashby |
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