• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Power tubes not drawing current

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redplater

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Joined 2010
#1
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!

Thanks!
David
 
#2
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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