Re: Calibrate the time base, or horizontal amplifier?


Zentronics42@...
 

Hi Harvey,
Well if there is a list of people that calibrate a scope to that extent. I will have to add my name to the list. I ended up building the lab based on the 7000 series scopes (7603 X2,7854,and 7904, and many associated plugins) but I had a chicken and egg issue. I got the scopes and plugins from eBay cheap but I did not trust them. A while later I ended up with both sets of cal standards the TM500 and the type units I still have a bit of work to do on the SG504 the high range is not working but low is. So I have done the full calibrations and everything is up to spec. It is a DEEEEEP rabbit hole that starts at a SG503 and ends at a type 284 and hits time mark and amplitude calibrators along the way. However in the service manuals the low frequency and high frequency compensations of the amps are done with square waves or various rise times and frequencies mostly around 1khz,10khz,100khz, rise times 1ns and higher for the high frequency compensations. I had to cal the calibrators before I used them so bas accuracy is against a Keithley 6500. All this was made reasonable when I called Tek for a calibration request. For a 465 they quoted me $100.00. for the 7603 frame $800 for a 485 $1200.00. I did not even ask about the 7854 and the 7904A. but given that I have done 3 7603’s a 7704A a few 465’s and 2 485’s as well as a partial on a 7854 ( need to recreate a board to complete that one unless the thermal calibration of the verticals is not that important don’t know yet. ) the gear was worth the investment. And the knowledge gained in doing the calibrations has been priceless.

In terms of AD/DC I have a fluke 343A for DC and a Fluke 5200A with the 5205A amplifier. The good news is for your needs you can get just the 5205A as it has a fixed gain and put the correct signal in the front end of it. If I remember correctly it is a gain of 100 so 60 V signal will output 600 Vac. As to for cost I don’t know. I paid $700 for both units broken. The amp was fine, however the 5200A -190V rail had burned up and the power amp in the 5200A needed to be rebuilt. Needed these to calibrate the 6 DM502’a. 6 DMMs is overkill however when working on the Tek multi rail power supplies it can be really convenient to watch them ALL at once. On thing to note on the meter cal does it need variable frequency? The 5200A with the 5205A can do 0-1200 Vac 10 Hz to 1 Mhz. Haven't needed to play with 1200Vac @ 1Mhz yet that is a bit spicey.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Harvey White
Sent: Sunday, July 11, 2021 8:56 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Calibrate the time base, or horizontal amplifier?

I'm not sure how well I can hear you, your voice is a bit echo-y from the bottom of that rabbit hole.

IMHO, what most people seem to worry about is horizontal and vertical accuracy, time and amplitude. You're quite correct that checking out the frequency response is difficult. The SG502 and SG503 are constant amplitude generators (at least the SG503 and SG504), and those can be used for frequency calibration. There are workarounds for fast risetime squarewave generators, which can be built easily. How much is a Fluke 5200? Thought they needed an amplifier for the high voltage output on AC. I personally can do DC 0-2 amps and 0-1KV. AC is a problem.

I do wonder how many people will calibrate a scope to that extent, unless the scope simply won't work without those sources. (the DM5101
*needs* a 600 volt measured AC source, but it's not a scope).

Harvey


On 7/11/2021 6:26 PM, Zentronics42@... wrote:
Harvey,
One of the main calibration issues that requires "exotic" signals Is the frequency calibration of the amplifiers. Having these be off can nuke the bandwidth of the scope. 465B 3db down 75-80 Mhz instead of 135 Mhz. (Yes I know 135 is above the 100 Mhz rating of the scope but that is what mine caled up to when properly adjusted.) These are done with fast edge square waves. 1ns rise time for 465 and under, ps rise time for 485's and faster for even further up the BW scale. But in terms of an AC calibrator a fluke 5200A would not be bad with its amp 5205A can go to I"1500 Vac. Which is a bit spicey. If using a meter something that needs to be taken in to account most good meters work in AC RMS scopes work in PK-PK so appropriate calculations need to be taken in to account when setting up the signal source. In terms of calibration a functioning and calibrated TG501, PG506, and SG503 will cover 99% of the scopes up to 100 Mhz. Over that will need "exotic" signal sources tunnel diode pulsers and such. I will admit I have seen the bottom of that rabbit hole it is kind of on the deep side.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Harvey
White
Sent: Sunday, July 11, 2021 6:14 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Calibrate the time base, or horizontal amplifier?

Not sure that they ever made one for the 5000 series, but an input standardizer would give you direct access to the frame, which would be fine if you had a known AC amplitude to calibrate the frame.

You'll only be able to get close, but remember that a scope is good to 3 to 5% anyway.

I'd be tempted to find an accurate AC source. A good meter would help, square waves would be best, but you'd need to adjust for the waveform if you're using a meter.

If you could feed a signal directly into the frame, then that allows you to calibrate both the H and V amplifiers.

If you have only the one frame, or only the one plugin, then I'd be tempted to take the mainframe's calibration on the Y channel as valid (arbitrary, I know), then adjust the vertical plugin to read the appropriate p-p value on the scope.

Then swap the H and V plugins (should be allowed, please check), but then adjust the H frame gain to the same deflection.

Then swap the plugins back to H and V. Adjust the H timebase for the appropriate scale.

that ought to get you close.

That's what I'd do. Adjusting the power supplies pretty much requires a recalibration.

A time mark generator can be made with some TTL logic and a TTL oscillator chip.

There are some amplitude calibrators used for a DMM that would give you at least a good 10 volt reference, so that range would be ok, but you'd find it difficult to check the other ranges.

Harvey


On 7/11/2021 5:28 PM, emissionlabs wrote:
Hello,

I need a little guidance, and don't want to make misakes while fixing a 5113 Dual Beam Scope. The 3400V high voltage was gone, and when I fixed that, the chopper circuit appeared bad, and when then was fixed, there was only one beam. Not mentioning a few smaller defects. But I have it all fixed now, and it works very good. Sharp traces, and very nice geometry.

I have adjusted the high voltage nicely at 3400V. +/-30V is as good as the single turn pot meter can do. +/-170V is allowed. Probably the HV is not exactly the same as it was before, and this affects the picture size, and if so, horizontal and vertical gain calibration needs to be done. I have two time base modules with it, which do not show the same result on the calibrator of the scope itself. So at least one of them is out of calibration. The horizontal trace is a tiny bit too slow, which can be caused by the horizontal amplifier being set wrong, or the time base being set wrong. I do not have a time mark generator, but I have an accurate hewlett packard pulse generator, which probably can do the same. And also we have 50 Hz here, and the internal calibrator shows exactly 100Hz. So a good reference is not the problem.

At this point I get stuck a little bit because I could set the horizontal gain a little bit higher, or set the time base a little bit faster. Both would "cure" the problem. But it feels wrong to set the time base faster, while in fact the horizontal amplifier would be out of calibration, or vice versa.

I have neve done this before, and I don't want to mess it up. It is such a crispy sharp CRT for the rest if it, I would like to get this scope in good condition. Perhaps someone has good advice for me. Thanks in advance!















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