Quote:
Originally Posted by David Simpson
Nick - many thanks for the revision. I can print off a nice pdf copy, but not the other - I don't have MS Office.
It would seem that the Roetest, my DC Tester, and the 163's are jolly close, but the older Mk3 & Mk4 struggle at achieving the higher Ia's. The Roetest's curve is mathematically perfect, but all the others exhibit the slight kinks.The kinks, I suspect, going by my own experience & some feedback from participants, are due to several factors. They are :- a) Wear & tear on Grid pots, b) switching between ranges on the grid volts switch & the meter switch's Ia range, c) age related deterioration of pots, shunts & multipliers, d) plain old human error(remember what I said last night about older Forum folk wearing glasses), e) the dynamics of the valve. . . . . . .
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David,
As you will know, the VCM163 grid voltage is set by a pot with the line on a see through (ish) plastic disc. The see through plastic disc is also some distance off the scale behind so parallax is almost guaranteed. I personally find it difficult to set that pot with any degree of accuracy and so if I want repeatable test results I set the grid volts by measurement on a DMM. Any kinks in my graph line are quite likely due to my imprecise setting of the grid volts.
That being said, I am impressed by the level of consistentcy of the results from all the testers. I have not worked it out but by eye it looks like plus or minus 5% which is fair enough.
regards, Nick