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Re: U64 - can anyone confirm this:
Author: Tim Dylla
Date: 10/28/2007
Hi Klaus,

thank you for your answer!
It's always a very similar ringing with any of my Nuvistors (I have checked 4 different Brands) - but I tried to locate the source by opening the housing and knocking on the components having the preamp on. It's the Nuvistor, this is very definite.
Since I don't have the best Instruments to measure components with high resistance and low capacity, I don't really believe in my measurements. So there is another explanation at hand: a wise guy from the vac-tube-era told me (if I remember right), that this effect could come from a misalignment of the operating voltages/currents the nuvistor is working on. He says, that it would explain why old nuvistors with a more flat characteristic curve ring less. He stated that Nuvistors are used in Tornados (you know, the dogfight-vessel), because transistors would disfunction when there is an EMP beside an atomic-bomb explosion (then, I think having an airplane crash is not the worst choice going to death, but that's rather off-topic). He says he doubts, that such a nuvistor is sensitive to vibration and physical shocks in normal circumstands. But he also states, the 7586 Nuvistor is originally built for RF-Frequencies, so maybe the unintended use for low-Frequency purposes can make it ring?

So this is my next question: could there be an alignment problem of the anode current or screen voltage that can cause this behaviour? When I measure the voltages at kathode and anode they seem pretty okay (used an Oscilloscope with 10MOhm restistance-probes, which is not much for this kind of cicuit, I think. The anode voltage is roughly 5% too low, but this could come from the Oscilloscopes probe the cathode voltage is inside specifications).

Thank you in advance,

Tim Dylla  
 
Reply
Tim Dylla
10/26/2007
Klaus Heyne
10/28/2007
Tim Dylla
10/28/2007
Tim Dylla
10/29/2007
Klaus Heyne
10/29/2007
Tim Dylla
10/29/2007
Klaus Heyne
10/29/2007
Tim Dylla
10/29/2007
Martin Schneider/Neumann
11/06/2007