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Old 13th Jul 2018, 3:33 pm   #12
Bazz4CQJ
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Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,920
Default Re: VCM163 Calibration Question

Although the 163 needs a fair bit of TLC at its current age, my experience over the last 10 years is that they are quite accurate and that the unique (?) mode of operation does indeed work well.

Referring to the recent exercise on this Forum initiated by David Simpson, that seemed to me to demonstrate that the well maintained 163's which participated in the exercise gave excellent results. Ultimately, the 163's service procedure does need to checked by using a reliably standardised valve. Using valves which I've DC standardised myself, and one from David, I've always been happy with the results for the 163.

An alternative "self check" method for the 163 is to draw the Vg-Ia curve of the valve just by carefully setting the Vg on the front panel control over a range of voltages around the nominal setting, noting Ia. You then have go and plot the results in Excel or similar, but what you should then get a value for gm which you can compare with what the 163 tells you on its gm meter. In my experience, those two values tend to be very close.

Over the years, I've used various valves as standards, but on the 163, a particularly good choice is an ECC81. A carefully selected one will have Ia and gm values which will be almost FSD on both meters on their lowest ranges, and will just about give adequate deflections for checking the meters out on the higher ranges.

My view of the 163 is that the build quality could have been improved, but it does deliver the goods!

B
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Last edited by Bazz4CQJ; 13th Jul 2018 at 3:43 pm.
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