From: cd6699@notformail.com   
      
   On Wed, 3 Sep 2025 16:55:15 +0100, Adrian Caspersz   
    wrote:   
      
   >On 03/09/2025 14:20, Cursitor Doom wrote:   
   >> Gentlemen,   
   >>   
   >> I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which   
   >> I'm trying to get fully working. Anyway, I have a problem with it   
   >> which I've never encountered before. I set the panels up to test a   
   >> valve, set the anode and heater voltages etc, the valves are glowing   
   >> just like they should, but when I apply the prods of a DVM across the   
   >> heater pins to check if they're correct WRT the switch setting, that   
   >> tiny extra load completely collapses the supply to the heaters! The   
   >> meter reads 0V (or close enough) and the heater glow dims to nothing.   
   >> Any idea WTF's going on here?   
   >   
   >If the circuit has any sort of gain, are you creating a feedback path   
   >with noise radiating cables that oscillates and overwhelms the power   
   >delivery of the supply? Try the meter switched to AC, or an   
   >oscilloscope, you may still see something.   
      
   Oh - by the way, the meter was switched to AC the whole time (and it   
   read the anode voltages accurately, too).   
   That valve tester could conceivably be repurposed as a damp detector,   
   if it's *that* sensitive to additional loading! :-D   
      
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