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Old 14th February 2011, 11:54 PM   #1
diyAudio Member
Join Date: Nov 2010
Default Power tubes not drawing current

I'm building an Eiclone monoblock stereo. It's an El34 ultralinear amp. Strangest thing. The tubes are not drawing any current. I've got like 570 vdc on the plates and -75 on the grids. It's not bad tubes....I've substituted two pairs and the same results. The tubes are drawing like 1 ma of current. The plates should be about 90 volts less. I'm baffled!

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Old 15th February 2011, 12:10 AM   #2
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Join Date: Feb 2008
Location: Niederösterreich
With the grids at -75v your tubes are in cutoff and cannot possibly pass much current at all. As you decrease the grids to closer to ~ -30v the tubes will start to conduct and your plate voltage will decrease due to the current draw. This amp is fixed bias?
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