[sdiy] A simple 12AX7 vacuum tube tester schematic..

[Scott Gravenhorst]

"Paul Perry" <pfperry at melbpc.org.au> wrote:
>There is little mystery to testing a valve for microphony, I imagine one
>simply runs an audio signal through it, and taps the valve itself, while
>watching the output.
>Any unhappiness will be only too visible (or even audible, if you do not
>have a scope).


Heh, yeah, I remember my dad working on TV sets we had years ago (all tubes) and he
would gently tap each tube while it was on and looked for perturbations in the
picture (for video section tubes) and thumping/popping/crackling sounds for audio
tubes.  I remember him using the word "microphonic".  Probably the first indicator is
that when someone would walk by the set, the picture or sound would go wonky. 
watching him fix TVs and radios was one of the things that got me started in this
field.  

-- ScottG

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-- Scott Gravenhorst
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