TEKTRONIX PRIMER ON PROBES ETC When the probe is first connected to the oscilloscope, compensate it by applying a low frequency square wave (1 to 10 kHz normally) to achieve the equalization of time constants. Improper compensation will result in either overshoot, roll-off or incorrect signal amplitudes (see Compensation Effects figure Probe Accessories). The charts on Oscilloscopes to Probes, Cross Reference give you information on specifications, oscilloscope compatibility and obsolete probe replacements to help you select the right probe for your application. Consider the Following Factors in Making Your Probe Selection: Match Probe to Scope Input Resistance and Input Capacitance - Be sure the desired probe will match the input resistance and capacitance of the oscilloscope being used. Fifty Ohm scope inputs will require 50 Ohm probes. One megohm scope inputs will require 1 megohm probes. Also check for connector interface compatibility or choose the appropriate adapter required. 1 megohm inputs may also be used with appropriate 50 Ohm adapters. Match to Scope Bandwidth and Rise Times - Select a probe with adequate rise time and bandwidth for the oscilloscope and application. Probe Loading Effects - Minimize probe loading effects by selecting low- impedance test points. Although the input impedance of a probe is made as high as possible, it still will always have some finite effect on the circuit under test. Usually cathodes, emitters and sources are preferred over plates, collectors or drains. Inputs to high-impedance dividers should be used rather than the midpoints. Be aware of the fact that the input impedance of a probe varies inversely with frequency. Example: A probe having a bandwidth of 50 MHz and an input resistance of 10 megaohm at DC would have an input resistance of approximately 1.5 Kilohm at 50 MHz. Choose the probe with the lowest possible input capacitance and highest input resistance for best overall signal fidelity. ------------------------------------------------------------------------------------------------------------ - Date: Thu, 15 Jul 1999 16:11:33 -0500 From: Terry Muncey <[email protected]> Subject: RE: Tek scope 502A -----Original Message----- Do you have the maintenance manual and schematics for this scope? Thanks in advance. W.Li Yes, catalog # R29127 cost is $51.80 (real big manual) + S&H, you can order direct on the web at http://www.radioera.com/order.htm if you want. ------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------- Date: Mon, 19 Jul 1999 15:47:50 +1000 From: Morris Odell <[email protected]> Subject: Re: [R-390] Tek scope 502A > nearly working Tek scope 502A for $40. Can anyone briefly send me some > specs?... before I lash out for the $51 manual. I love test equipment too and in fact a 502 was my first Tek scope - I still have it in the basement storeroom. The 502(A) was a high sensitivity true double beam scope which was sold to biological research and electrophysiology labs. It uses a special double gun double beam CRT and thus has two completely independent vertical channels without alternate or chopped trace facility. The timebase is common to both beams. The very sensitive narrow band DC coupled vertical amps achieve 1 MHz bandwidth at the low sensitivity end, falling to about 100 KHz at 200 microvolts per cm. The amps are shock mounted and contain Telefunken 12AX7s that are prized by the audiophoole community. Their heaters are run from DC. The rest of it (HV supply, timebase, calibrator) are typical Tek circuits of the 530/540 type. The 502 power supply is a bit different from the 530/540 series in that it uses vacuum tube rectifiers (? less noisy) so there's no time delay relay . It's quite a nice scope for DC and audio measurements but useless for RF. The amplifier response falls off very quickly above the spec limit. I remember my 502 as being rather difficult to keep in spec with regard to intensity balance. The HV circuitry is set up in such as way that the relative intensity of the two beams is balanced with a preset pot. It used to drift quite a bit as it warmed up. Not a fatal fault but it could be irritating. I liked it a lot and used it on the bench for a good few years until a 535A came my way. 73 de Morris VK3DOC ------------------------------------------------------------------------------------------------------ Date: Mon, 19 Jul 1999 04:47:00 -0700 From: Dan 'Hank' Arney <[email protected]> Subject: Re: [R-390] Tek scope 502A Call Deane Kidd in Sherwood.OR. he is listed in the book. He has manuals and parts. Very good reliable service, and the prices are also good. Hank -------------------------------------------------------------------------------------------------------- Date: Mon, 19 Jul 1999 08:18:18 -0700 From: [email protected] Subject: Re: [R-390] Tek scope 502A If Nolan can't find his manual, let me know, and if you still need the specs I can copy a few pages of the manual for you. Jan ----------------------------------------------------------------------------------------------------- Date: Mon, 19 Jul 1999 03:15:38 -0500 From: Nolan Lee <[email protected]> Subject: Re: [R-390] Tek scope 502A Traffic has been low. Well, up until I triggered a near riot that is...It's a true dual beam with a bandwidth of about 1 Mhz if I remember right. .... Email me back with the exact model number and if it's a rack mount model or not and the serial number of the scope. I owned a few of 502's and 502A's and probably still have an original manual in the correct SN range that I'll make you a good deal on. Photocopies of the old Tek scope manuals usually suck on account of a lot of the test measurement values being printed in them in light blue which doesn't copy worth a damn. ------------------------------------------------------------------------------------------------------------ - Date: Mon, 19 Jul 1999 10:25:41 -0400 From: Christian Fandt <[email protected]> Subject: Re: [R-390] Tek scope 502A Yes, about 1 MHz for sure. Nolan means that there are actually two electron guns in the CRT thus making it a 'true' dual beam as opposed to the typical dual beamers which simply alternate which of the two input channels are sent to the single-gun CRT. Great for catching short duration events which could be distorted or even hidden by the switching action. >>before I lash out for the $51 manual from RadioEraArchives.... $51? Ouch! Seems kinda high but who cares what they sell it for: everybody's permitted to shop around ;) That's right. Some copiers will copy the blue though. I recall those were the ones which used a white light source as opposed to the ones with greenish exposure lamps. Look for those if you need to copy such things. ---------------------------------------------------------------------------------------------------------- Date: Mon, 19 Jul 1999 11:07:14 -0600 (MDT) From: Richard Loken <[email protected]> Subject: Re: [R-390] Tek scope 502A Those are called dual trace scopes not dual beam scopes. Philips used to make some dual beam scopes back when I was in technical school circa 1970. Nice scopes which put everybody to shame except Tek and HP (in that order). -------------------------------------------------------------------------------------------------------- Date: Mon, 19 Jul 1999 14:14:13 -0500 From: Nolan Lee <[email protected]> Subject: Re: [R-390] Tek scope 502A It's been a few years since I've owned any of them, but I seem to remember that Tektronix actually used the wording Dual Beam on the front panel and in the manuals to differentiate between them and the less expensive Dual Trace scopes. The CRT used separate guns, and deflection plates for each of the two channels for a really nice non-flicker display. You could set one beam to sweep at say a second and the other at a ms and each trace would display 100% of the time, there was no "switching" back and forth. It's too bad that the bandwidth of the 500 and 502A were only a Mhz or so. Come to think of it, I think that the 502A had more bandwidth than the 502. Maybe it was a 2 Mhz scope, or it was the 1Mhz one and the 502 was a 500Khz scope. I need to dig around and find the manuals to be sure. The 502 and 502A were common as dirt around the New Orleans area about 15 years ago. NASA Michoud and Stennis Space Center cut a bunch of them loose on the surplus market along with a mess of the higher numbered models and thousands of plug-ins. almost everything that was sold off was "current" as far as calibration certification. You don't see that much anymore. >Philips used to make some dual beam scopes back when I was in technical school circa 1970. Nice scopes which put everybody to shame except Tek and HP (in that order). Those old Tektronix 500 series scopes were true works of art. Wonderful examples of quality craftsmanship. ------------------------------------------------------------------------------------------------------------ - Date: Mon, 19 Jul 1999 14:51:46 -0700 From: [email protected] Subject: Re: [R-390] Tek scope 502A >It's been a few years since I've owned any of them, but I seem to >remember that Tektronix actually used the wording Dual Beam on the >front panel and in the manuals to differentiate between them and the >less expensive Dual Trace scopes. Sure did - I'm looking at the manual and scope as I hunt and peck. >The CRT used separate guns, and deflection plates for each of the >two channels for a really nice non-flicker display. You could set one >beem to sweep at say a second and the other at a ms and each trace >would display 100% of the time, there was no "switching" back and forth.