Jim Adney wrote:
On Sun, 19 Dec 2004 Damian Menscher wrote:
Jim Adney wrote:
On Thu, 16 Dec 2004 Damian Menscher wrote:

A pet project for the past several years is repairing an ancient
Tektronix 674 oscilloscope.

674? What's that? Is there a typo there?

Sorry, it's the 647. And the tubes are 5642s, not 5647s. Apparently
it doesn't work to remember numbers after it's been 2-3 years.

How about 547? Does that sound any more familiar? ;-)

No, it's definitely a 647. Got it right here in front of me. Looks
to be one of the earlier ones, judging by the serial number.

It has a strange malfunction which I've been trying (unsuccessfully)
to correct for the past 10 years or so. I'll start a new thread about
that, though, since it has little to do with this thread.

Could you buy 10 MOhm resistors, and then just use your 10 MOhm meter
as the last resistor in the chain? That would reduce the load on your
test point by a factor of 10, which would be a good thing.

Radio Shack doesn't have anything larger than 1 MOhm. Hence my idea
to use so many of them. I suppose I could add more to the chain,
though. Or I could just get a real HV probe....

If you really want to do this, let me know and I'll see if I can come
up with 90 MOhms of resistors to send you. (In the suggestion above, I
meant to suggest that you use nine rather than ten 10 MOhm resistors
in series with your 10 MOhm voltmeter.

You'll have to explain to me how to use the meter as part of the
chain... that doesn't really make sense to me. Also, doesn't that
impact the safety of the measurement?

Does your voltmeter have a 10 MOhm input impedance? What model is it?

Yes, it does. It's a BK Precision 2703B. Spec sheet is available
online at:
http://www.bkprecision.com/www/np_pdf.asp?m=2703B
and shows a 10 MOhm resistance for DC measurements (which is what I'm
planning to do with it.

Damian Menscher
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