Quote:
Originally Posted by Mike Brett
As this is my first test I am not really sure what to expect so would like a little help if possible.
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Mike,
I would grab the valve data sheet and look at the chart of grid voltage versus anode current. You'll see a slope which you can test on the Sussex by charting the Ia against a number of specified Vg points. This slope should be quite close to the 'book' value, and should be indicated quite accurately on the Gm meter, which reads mA/V.
I have tried several EF86 valves, most of which perform below the 'book' values. I have also tested a valve of known characteristics and found that my Sussex gave me the correct reading on the Gm meter, and when I plotted the characteristic mA/V slope it was exactly the same as one plotted on a CT160.
Don't forget that the 'book' test involves the ECC83 anodes being shorted together and the valve being tested as one unit. Maybe time for another toggle switch?
The will also be some variations in Gm readings if the Vh is slightly off 'optimal'. My Sussex has a Vh on the 6.3V setting of 6.74V so that will account for some of the differences I get in my readings. I don't see this as an issue, however, because once I have 'calibrated' the Sussex I will always know how much it over- or under-reads.
I am setting out on a scheme to map all the valves I have on the shelf (not too many, I service vintage instrument and PA amps mostly and my stocks are a quite limited range) against the data sheets, so I know which of my valves are close to spec, and how far out the Sussex really is. So far, it has been remarkably close to the text book!
Hope this helps,
Richard