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Oscillation in tube amps
Oscillation in tube amps
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Old 14th February 2018, 12:04 AM   #141
multi is offline multi  Australia
diyAudio Member
Join Date: Jan 2011
Hpeter wrote:
"Audio tubes are not very steep, but when you use uhf mega steep tube.. You asking for trouble"
Has anyone built an amp using uhf mega steep tubes or just using theory?? Can you use the normal ways to control oscillation?
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Old 14th February 2018, 01:05 AM   #142
Johan Potgieter is offline Johan Potgieter  South Africa
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Join Date: May 2005
Location: Pretoria, South Africa
Is 20 mS steep enough? Working quite well in a low noise audio pre-amp.

I mention AGAIN, as others also did:

No component governs results on its own. A circuit performs/misperforms because all the elements contribute. A 400 MHz spec. only indicates that said tube is capable of working there, all else being in order at that frequency, including the operating point of said tube.

Occasionally graphs are available showing tube characteristics at other than the tested Ia. 'Steepness' (gm) can easily drop to a fraction of the test value when using a tube at lower current than tested, as is usually the case in audio - then no longer a '400 MHz' tube.
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Old 14th February 2018, 01:42 AM   #143
multi is offline multi  Australia
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Join Date: Jan 2011
Johan Potgieter
That is what i was thinking.
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