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Old 12th May 2006, 02:20 PM   #1
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Default Will I kill my Tek 2213

Hi all,

I just got my Tektronix 2213A its rated for 400V pk - pk, I buy it to take mesurement on my tube amp project. But I got around 425V on my psu, if I scope this, will I kill it ? What can I do ? I got right now a 10x probe tek 6121, does it exist a 20x or a 25x to take such mesurement ? Thank in advance
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Old 12th May 2006, 02:45 PM   #2
anatech is offline anatech  Canada
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Hi guitvinny,
High voltage probes are available. They are generally 100:1. You must start at the highest V/div range even when on AC. Please always do this or you may damage the input circuit.

If you kill your 'scope (hope not!) I may need the knobs

I try to use older (non-IC front end) type scopes when working with tube amps. They can take a little more abuse and survive. They are also repairable whereas the IC types are not generally. Tek stopped supporting your model around 11 years ago I think (like mine).

-Chris
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Old 12th May 2006, 03:08 PM   #3
Eva is offline Eva  Spain
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Get a good 100:1 high voltage probe rated above 1000V. It's a must for that kind of work.

Also, the voltage dividers of the lower voltage probes will tend to break down with high AC voltages when used in 10x mode, thus providing an erratic measurement.
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Old 12th May 2006, 04:37 PM   #4
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Thank alot ! I`ll start looking on ebay ... but on my scope it said : max 400 pk - pk max .... So will I kill it by using a 1000 V probe 100x atten. ??
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Old 12th May 2006, 05:08 PM   #5
Eva is offline Eva  Spain
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The attenuation is done on the probe, so only 1/10th or 1/100th of the measured voltage will be fed to the input of the oscilloscope as long as the probe attenuator is not overstressed causing insulation breakdown.

The inputs of mine are also rated at "400V max." and my 1x/10x standard probes are rated at 600V peak, but I don't feel like testing these ratings
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Old 12th May 2006, 06:51 PM   #6
Stocker is offline Stocker  United States
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Anatech, you have email about the knobs.

Guitvinny, almost any recent multimeter will do a good job of measuring 400+ Volts AC or DC directly. I would use one before risking an oscilloscope. Even a very inexpensive meter would be good enough to get an idea of what is happening in your circruit.
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Old 12th May 2006, 08:01 PM   #7
anatech is offline anatech  Canada
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Hi Stocker,
You have mail back! Thank you very much. EC8010 is sending some knobs which I hope will fit. We will see, as they are due here in a week or so.

Again, thank you!

-Chris
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Old 14th May 2006, 07:54 AM   #8
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Got some ideas for ya.

Ive got a 2235 here and it has a warning not to put more than 400vdc when using AC coupling. Couple that with a p to p and your running into dangerous ground. That coupling cap can break down and psssssssst there goes your front end.

Tek did make a 100 to 1 probe, but it was expensive and hard to use.

Another way to do this is...

If you have Tek P6122 probe for example they read

10M ohm
11.0pf
10x

If you hang a 100m ohm resistor in front of the probe, that will give you a rough 10 to 1 divider, using the internal resistance of the existing probe. It's cheezey but it works.

The other trick is not to measure the high voltage directly but use you output transformer's output and see if that's proper. It might save you some expensive parts.

Also what Mr Stocker said about standard multi meters.

On the old Simpson 260's (remember them) there is an 'output' jack that has a dc blocking cap in line with the measurment element, so you see just the AC part of the signal. Read the manual and learn how to use this feature. It's been 20 + years since I last calibrated one so memmory can be a touch fuzzy.

One last idea, make a small coil and wrap it around the high voltage line (well insulated). Then feed your scope the output from that coil. The scaling might be screwey but you will get an idea what the wave is doing.

I presume your looking for cliping p/s sag and other such problems.

Much luck
Jack Crow in Kuwait
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Old 14th May 2006, 03:00 PM   #9
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Quote:
Originally posted by Eva

The inputs of mine are also rated at "400V max." and my 1x/10x standard probes are rated at 600V peak, but I don't feel like testing these ratings
I commonly use standard x10 probes on TV line output stages, and have done for a number of decades - I've had perhaps two probes die in all that time, but only after years of use. With the scope on 10V/cm and a x10 probe, the pulses are greater than the screen height, around 1000V at 15,625Hz.

Another reason NOT to use Tek scopes, generally their highest range is only 5V/cm! - at least on the ones I've seen and tested.

Carrying on from a point someone else mentioned, there's generally very little use for a scope in valve amplifiers anyway, a simple cheap meter does almost anything you need.
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Old 14th May 2006, 04:40 PM   #10
Eva is offline Eva  Spain
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In a TV line stage you don't even have to touch the circuit with the probe tip, just place it closer to the switching nodes and you will see all the waveforms

A loop antenna made by connecting the ground lead to the tip of the probe also allows to see TV switching waveforms
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