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Old 18th October 2004, 11:24 AM   #21
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Quote:
Originally posted by tekman

Okay, that's muc hmore than you really need for audio.
but, refering to Jim Williams artciel in edn in 1995 about taking care care of personal equipment: A good probe last's appr. a year i nthe industry, bt most times more than 20 years in your personal diy lab. So, it does not matter much to me if I bay 20 $ for a no-brand probe or a 60 $ fora well working used Tektronix P6137. That's lees difference than a billet for cinema per year -- but I am shure I am better of with the Tektronix.
the reason they last longer in a DIY lab is that your wife is unlikely to swipe them -- OTOH, if you have sons who are majoring in electrical engineering they are just as likely to have the short half-life Williams describes.
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Old 18th October 2004, 04:56 PM   #22
Thomas is offline Thomas  Denmark
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Quote:
Originally posted by tekman
2 Thomas: Yes, Singer has a lot of stuff. He is in the business

......

The risetime rule of thumb I can't state as valid. Usually, a probes risetime of e.g. 3.5 ns is alright for a 100Mhz scope (which is a 3.5 scope risetime, considering:

Hi all, and thanks for the help.

Personaly I don't mind paying a bit more, knowing the quality is ok. The stuff he sells are checked (i trust). The best thing would be to check the items yourself. Not having that option it's better to be safe than sorry.

I bourght some 100 MHz Hewlett Packard probes. They should be allright, I think. (I like their calculators and printers, so why not? )
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Old 19th October 2004, 10:15 AM   #23
tekman is offline tekman  Germany
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2 Thomas:

Despite your favour for HP calculators, be careful with these probes.

It's not only the BW of 100MHz to look at. Also a must is to check the probe's compensatio nrange. At HP you mostoften see it printed on the compensation box (p. ex.: 18 to 27 pF) of the probe.

your scopes input should fit into this range. E.g: If you have a 1Mohm 35 pF scope input, you will not be able to compensate the 10:1 divider probe correctly if probe's range is 11-25 pF.

You see, it is not always that easy to get the right probe:

1. Bandwith
2. Compenastion range.
3. max allowable input voltage (sometimes for Tube amps or TV application)
4. length of cable (rule of thumb: most probes are offered with 1.3m, 2m, 3m options. Take the shortest cable that fits your needs to keep capacitve load low and BW high).

You will be alright with a 10:1 10/1Mohm probe in 99% of audio work applications.

Fet probes are nice for criticical points, but have low voltage range and are easily overdriven. You hardly need these.

HV probes (1000:1, up to 40kV peak): well, if you extend your audio tube map work to X-Ray tubes, you might consider this.

Current probes: Not in the beginning, but for serious work a "must have". There a AC only and combined AC/DC probes around. I'd go for the combined ones: Eases work if you bias set an amp, just clip around the emitter/drain connection and set the value. As far as I remember the tek P6403 is a DC-50 MHz classic. If you get it for a reasonable price and the probe is working (the hall device is hard to replace), go for it.


good luck!
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Old 19th October 2004, 01:18 PM   #24
Thomas is offline Thomas  Denmark
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Quote:
Originally posted by tekman

1. Bandwith
2. Compenastion range.
3. max allowable input voltage (sometimes for Tube amps or TV application)
4. length of cable (rule of thumb: most probes are offered with 1.3m, 2m, 3m options. Take the shortest cable that fits your needs to keep capacitve load low and BW high).


Hi tekman,

The HP 10004D probes is in the 20-30pf range. The Philips scope is 20pf. It is close to the limit, but I should be allright with them. Also they are only 1m long,

So far, all my projects was done with a DMM, but ofcouse there are limits. I was lucky enough not to need the faultfinding capabilities, because everything worked the first time.

My newest project is different though: repairing philips laser pickups. The first thing I will be meassureing is eye patern. Later, I will use the scope to look at the digital clock about at 12MHz and for various Aleph and gainclone building. I'wont use the scope for high voltage meassurements, but a current probe would be nice to have around when building amps.

This thread is growing into a goldmine of info for first time scope buyers. Thanks a lot, guys.
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Old 20th October 2004, 07:05 AM   #25
tekman is offline tekman  Germany
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hi Thomas,

this looks fine for the probe. It should work.

Laser pickups: That'S how I work onit:

Most time you only need a re-adjustmend of the laser diode current pot. It's located near the diode. And a CD. I Put the CD in the player, re-adjust the pot carefully until the player shurely recognises and playsthe CD. That's it. No scope ever switched on for this
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