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Electronics => Repair => Topic started by: Johnny10 on January 10, 2017, 02:01:03 pm

Title: Tektronix 576 HV Power Supply troubleshooting HV Probe Recommendations
Post by: Johnny10 on January 10, 2017, 02:01:03 pm

I recently acquired a Tektronix 576 Curve Tracer B28xxxx serial number I believe from late 60's.
The CRT image flashes and dims and sometimes drifts after initial warm-up.
I checked all LV voltages and all measure within spec. and stay in proper range throughout my problem.
The 225 VDC measures from 199VDC through to 177VDC.

I have Fluke 87 for measuring voltages and cannot measure 4000 volt circuits.

I need a recommendation for High Voltage probes to measure CRT circuits.

One for DMM and one for Analog Oscilloscope.

Maybe something in $50 dollar range if possible.

Title: Re: Tektronix 576 HV Power Supply troubleshooting HV Probe Recommendations
Post by: PaulAm on January 10, 2017, 07:00:16 pm

If 6KV is good enough, there's a Fluke 80K-6 on ebay for $30 bin right now.  There's also one at $47 with a make offer.

If you need more than 6Kv, look for a Fluke 80K-40 which is good for 40Kv.  Either will work with most DVMs

At least if you're in the US.

Title: Re: Tektronix 576 HV Power Supply troubleshooting HV Probe Recommendations
Post by: David Hess on January 10, 2017, 08:08:17 pm

I have no complaints about the Fluke 80K-6 which I bought off of Ebay for exactly this sort of application.  The CRT cathode voltage is relatively low impedance and generally between -2000 and -4000 volts so the 75 megohm input resistance of the inexpensive 80K-6 is not a problem.  If you want to read the voltages from other CRT elements, then the 1 gigohm input resistance of the 80K-40 or 80K-15 will be better and of course the higher voltage probe is needed to measure any PDA (post deflection acceleration) voltage but this is seldom necessary.  These probes expect a voltmeter with a 10 megohm input resistance for accurate measurements.

A high voltage oscilloscope measurement is very rarely needed for CRT work but if you must, then the best options come down to a used Tektronix P6013 or P6015 which include shunt terminations.  These probes can also be used with a voltmeter if a 1 megohm termination is present.

Beware that new x100 high voltage probes that have a 100 megohm input resistance do not include a shunt termination and cannot be used safely with AC coupling without risking damage to the oscilloscope.