Scope probes

[HBrown]

I have a Tektronix 2235A on its way to me with no probes- can someone recommend the best option for probes for general use? I intend to stay with Tek brand probes, unless the group opinion is there is no valid reason to. Money is an object, but I will spend what I need to get the proper probes.
I have seen Tek P6122 & P6109 associated with the 2235 scope. What would you go with?

 

[JURB]

For general use ? The cheapest you can find. A scope probe is a cable with an attenuator. The cable part is what limits the bandwidth. In actual practice, I would prefer a longer one with a lower bandwidth than a shorter one with higher. If you want to do TDR, that is a different story.

There are few scope probes on the market less than 100 MHz.

One place you might want to look is TEQUIPMENT.COM. They carry Velleman, which seems to have good prices. Problem with them is the minimum order. Maybe a few of us get together and get a bunch of them.

I tell you this - get extras. When you use a scope probe it will wear out.

The other thing, try to get probes with the 100 MHz bandwidth to match the scope. Otherwise in 10X it might not calibrate properly. You can look at the spec on the scope, It might say like 10 pF. The scope probe has to be adjustable to one tenth of that. If you get lower bandwidth probes, just make sure they can adjust to one tenth the input capacitance of the scope. It will work fine for audio.

When you get to the fancy probes, keep them locked up. Probes get knocked up. For general use, use the elcheapos. When you start getting into TDR that is different. (TDR stands for Time Domain Reflectometry which is a test for RF transmission through cables of supposedly a specific impedance, and a 100 MHz scope would not be able to do it very effectively)

Soon, I will probably post about how to make testers of other sorts out of a scope. This used to be a trade secret. Not no mo. The trick is learning to read the trace. Before I post that I need to gather up some pictures to illustrate.

In time.

I got too much **** gong on right now.

 

[HBrown]

I'm not totally sure what the difference in just a 2235 scope and the 2235A scope- I was able to find a manual on-line for the 2235, and it said they were shipped with P6122 probes.

I'll get a pair of cheap probes to knock around with, but would like the correct ones to have and keep the scope like original.

Does anyone know the difference the 'A' makes, or be able to verify what the 2235A came with as far as probes?

 

[njcanuck]

I like TPI brand sold by Mouser, DigiKey, eBay for general purpose stuff. FWIW I got rid of my older Tek probes because the cable was thick and not very manageable. Maybe the newer ones are better?

 

[whoaru99]

I use the TPI also. Seem to work fine for what I do.

Looks like it's a 100MHz scope so 100MHz probes if you plan to use full capacity (although largely unnecessary for general audio, I think).

 

[NYListens]

I bought mine off ebay, have had no issues wirh them

 

[gadget73]

I did some research on those cheap of the cheap ebay probes. The guys that know such things on EEVblog say they are actually quite decent, and amazingly so for the tiny money they cost. I ran a set for years before running one over with my chair. I have a replacement pair on the way. Still running a solo probe at the moment.

One thing I will say is that the ground clips suck. Both of mine broke the wire internally where it connects to the clip going around the barrel of the probe itself. I cut the factory plastic blob off, soldered the wire back on, and put some heat shrink over it. Easy peasy, but its just something to be aware of if you start seeing a lot of noise on the screen that cuts in and out randomly.

 

[JURB]

your probes do not have not be married with the scope. As long as the capacitance is close enough you can calibrate it. In the 10X position you connect it to the probe calibrator and adjust the trimmer in the probe for a flat line on the square wave.That is it.

In 1 X it will be right, if it is not, the scope itself is at fault and you need someone who knows what they're doing to straighten that out. but that is not all that common. I ran ionto it on an HP 1725A where someone tried to retrofit a home made replacement for the vertical output IC.
You just don't do that on an analog 275 MHz scope. Actually I tried and got it alot better but the last guy FUBARed the alignment. I got it trustable up to about 80 meg.

When you first buy a used scope you should take just a wire from the probe calibrator and hook it direct to the input and make sure you get a nice square wave. As long as you got that, you can be reasonably assured it is in alignment. Don't etch that in stone, but it is a good indicator.

Higher frequency square waves tell alot more. The 1 KHz is just to set the probes, nothing like a real alignment. When you get to that, you can buy ten grand in equipment or you can bring it here. Seriously. But usually it is not needed. That 1725 had been seriously screwed with, with the guy trying to calibrate it to the wrong circuit. I got a circuit off the internet that cam alot closer than the POS he rigged in there, but I could not get enough gain out of it. Then I got my grubby little hands on one of those unobtainium chips and put it in. It is still off but it is alot closer than it was. I do not have the equipment at this time to get it any closer. I could probably do a 100 MHz, but a 275 is a bit too much.

I really like to stay away from the vertical circuit in scopes. They are like tuners. I can set them up, calibrate them but with my methods I cannot claim official accuracy. you have to buy a binch of stuff, pay money, go to a class, pay more money and then take the test and then pay more money to make your little ink stamp on the unit worth something. Usually goes on stickers that must be breached to open or adjust the unit.

Part of this is trying to be accurate and part is money. Like ISO9002, if you work for an ISO9002 compliant company you are not allowed to modify any test equipment (which engineers want to do all the time) and every screw has to be accounted for and all that. this is because of money, because the assets of that company must be reported accurately because it is publicly traded. If you take a plugin for a Tek scope and modify the input for whatever reason, the company you work for just committed fraud. that is the law.

OK, sorry I got so long.

 

[for_p1]

The only thing I would add - if you get probes, find ones rated at least 3 times nmoire than scope. Like 300 MHz ones for 100 MHz scope. That way you minimize error in high frequencies. Also if you plan to work on circuits with more than 200 volts - get 100x CAT IV porobe rated for 1000 volts. Moist standard 10x probes are only good for low voltage measurements.

 

[JURB]

Yup. in a way you are right. A scope is rated at its -3 dB point. If you have a probe rated the same, then that is a -6 dB point.

But this means nothing in audio. Spend the money or not. (and it isn't that much really)

T^T