AVO VCM163 oddity

mobyd · 2nd April 2010, 10:17 PM

My 163 has a very odd habit. Whenever I test a twin triode (ECC3x,ECC8x) the second triode almost invariably reads lower than the first (Ia and Gm) usually by about 10-15%. One would think there would be a 50/50 distribution of first and second triodes reading lower (if at all).
Any ideas ?
M

tomchr · 2nd April 2010, 10:59 PM

What are the tolerances of the parts used in the tester? Older gear often has +/-10 % tolerance resistors (indicated by a silver band at one end). That would explain why there seems to be a systematic offset in the tester.

If you have a tube socket handy, you could try measuring the same triode in position 'A' and 'B' on the tester. That should yield the same results. If it doesn't, I'd look for component variability, switch point corrosion, cold solder joints, etc.

~Tom

2nd April 2010, 10:17 PM	#1
mobyd diyAudio Member Join Date: Sep 2004 Location: Auckland	AVO VCM163 oddity My 163 has a very odd habit. Whenever I test a twin triode (ECC3x,ECC8x) the second triode almost invariably reads lower than the first (Ia and Gm) usually by about 10-15%. One would think there would be a 50/50 distribution of first and second triodes reading lower (if at all). Any ideas ? M

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2nd April 2010, 10:59 PM	#2
tomchr diyAudio Member Join Date: Feb 2009 Location: Greater Seattle Area	What are the tolerances of the parts used in the tester? Older gear often has +/-10 % tolerance resistors (indicated by a silver band at one end). That would explain why there seems to be a systematic offset in the tester. If you have a tube socket handy, you could try measuring the same triode in position 'A' and 'B' on the tester. That should yield the same results. If it doesn't, I'd look for component variability, switch point corrosion, cold solder joints, etc. ~Tom

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