Test Equipment: Oscillocopes

[Brian516]

Hopefully they use nichrome coax cores.  Please let me know how they perform once you get them.

Most certainly will do.  If they aren't molded shut, I'll open them up and see what kind of coax core they have. 
The reason I went with those is because they've sold hundreds of them and have a 100% positive feedback rating, and are a top rated seller as well.   I have my fingers crossed they use nichrome........

[Brian516]

Do the BNC patch cables that you use have nichrome coax cores?  Cuz I noticed that most BNC patch cables are RG58 or RG59.  I got some BNC/RG6 compression connectors at RadioShack, and I have several different kinds of RG6 - the best being XFT, and also Eagle Aspen 3.0Ghz RG6. All of it is 18AWG copper core, though.

Also, I took my scope apart and took the preamp board off.  I detailed everything with IPA and cleaned all the switch contacts and finger contacts with deoxit D5 and then IPA. I made sure I got the 91% IPA, which is pretty much the best I could find.  I'm not taking any of the other boards off unless I have to due to desoldering, but there is absolutely no visible damage to anything on the preamp board, so I switched the attenuators around from CH1 to CH2 and vice verse, so if CH2 works and CH1 doesn't, I know what part is broken.  Otherwise, I'm going to end up going thru all the tests/calibration steps one by one until I figure it out... since its $365 to calibrate professionally, and the service centers stopped doing repairs on the 465 in 1994...    If it isn't the attenuators and is something else, I will hook it up with a direct line to the calibrator and make a vid showing what it's doing.   Hopefully I've fixed the V/div issue at least, though.

One more thing, my unit has attenuators for 100X - so I guess it would automatically adjust the readouts for a 100X probe. Unless that means something completely different from what I am thinking.

[MarkE]

Most certainly will do.  If they aren't molded shut, I'll open them up and see what kind of coax core they have. 
The reason I went with those is because they've sold hundreds of them and have a 100% positive feedback rating, and are a top rated seller as well.   I have my fingers crossed they use nichrome........

I bought some "200MHz" probes that were about the same price, but the appearance is different.  They were very so-so.  Hopefully what you've bought will be better.

[MarkE]

Do the BNC patch cables that you use have nichrome coax cores?  Cuz I noticed that most BNC patch cables are RG58 or RG59.  I got some BNC/RG6 compression connectors at RadioShack, and I have several different kinds of RG6 - the best being XFT, and also Eagle Aspen 3.0Ghz RG6. All of it is 18AWG copper core, though.

Also, I took my scope apart and took the preamp board off.  I detailed everything with IPA and cleaned all the switch contacts and finger contacts with deoxit D5 and then IPA. I made sure I got the 91% IPA, which is pretty much the best I could find.  I'm not taking any of the other boards off unless I have to due to desoldering, but there is absolutely no visible damage to anything on the preamp board, so I switched the attenuators around from CH1 to CH2 and vice verse, so if CH2 works and CH1 doesn't, I know what part is broken.  Otherwise, I'm going to end up going thru all the tests/calibration steps one by one until I figure it out... since its $365 to calibrate professionally, and the service centers stopped doing repairs on the 465 in 1994...    If it isn't the attenuators and is something else, I will hook it up with a direct line to the calibrator and make a vid showing what it's doing.   Hopefully I've fixed the V/div issue at least, though.

One more thing, my unit has attenuators for 100X - so I guess it would automatically adjust the readouts for a 100X probe. Unless that means something completely different from what I am thinking.

You only want nichrome in the scope probes.  In the coax you want low loss copper.  The flattest response probe that you can get or make is called a transmission line probe:  The coax cable is matched by its characteristic impedance at the input to the scope: typically 50 Ohms.  $5000. and up scopes typically have a 50 Ohm / 1 MOhm input impedance control.  For the rest of us poor slobs, you can buy a male / female 50 Ohm through termination.  The coax cable would then load your circuit with 50 Ohms, which is a bit much for most circuits.  So, what Tek and Keysight offer are those kinds of probes with a series resistor.  A 450 Ohm series resistor makes a 10:1 voltage divider with the impedance of the cable and the circuit sees 500 Ohms instead of 50 Ohms.  The Tek probe is a P6150.  Keysight offers a probe with a 950 Ohm series resistor, that makes 1000 Ohms to the circuit and 20:1 attenuation.  It's a 1980's design.  I would have to look up the part number.  You can make a probe tip yourself or scrounge around eBay for one of the probes I mentioned.  Usually people want way too much money, but they pop up now and again for $100.-$150.

[Brian516]

So I have been doing a bit of research on what type of Coax wire to use for home-made probes.
This is the info I found, and the material I chose.   I want to see what you think about these materials.

https://en.wikipedia.org/wiki/Coaxial_cable

I chose RG316/U as the best possible candidate.
This type of cable is used in Nuclear Instrumentation Electronics.
Here is a link to an ebay item that has more info on the specs of the cable.

http://www.ebay.com/itm/10-ft-RG316-U-RG316-Equiv-Excellent-Quality-Coax-Cable-USA-SELLER-FREE-SHIPPING-/251237252458?pt=LH_DefaultDomain_0&hash=item3a7ee83d6a
http://www.ebay.com/itm/RG-316-MIL-C-17-Coax-Cable-50-Feet-/221625146764?pt=LH_DefaultDomain_0&hash=item3399e35d8c
I had to look up the "core material" - turns out SPCCS is Silver Plated Copper Coated Steel.


Here is some other cable with a much, much higher attenuation. It is "rg8X"
http://www.ebay.com/itm/USA-MADE-RG8X-95-SHEILDED-HAND-SOLDERED-50FT-CB-HAM-COAX-RADIO-CABLE-PL259-/170974652520?pt=LH_DefaultDomain_0&hash=item27cee22868

I wasn't able to figure out or find the exact kind of wire that is used for probes, so the only thing I can think of to find out would be to call Tek or another company that manufactures them and ask, or see if I could get one of the smaller probe manufacturers to tell me, which I doubt they would since there is only one reason why I would want to know - to get some and make my own!!

So what are your thoughts on this? I know that just buying some high quality probes is the best way to go, but what I am thinking about here is the possibility of making my own probes that are similar in performance to the extremely expensive probes that are on the market.  It'll be easy enough to make my own spring-loaded tips out of other types of hook tips that are out there, and easy enough to make my own connector base units for the resistors, caps, and adjuster.  If I don't feel like doing it by hand, I could just get someone with a small CNC machine to make them for me.    If this works out, and the performance is good, I'm sure this could turn into a new way for us who can't afford a $500+ dollar probe to make some that are "good enough".

Brian