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In the Forum: Melquiades Amplifier
In the Thread: R22
Post Subject: Much too much currentPosted by JJ Triode on: 1/1/2022
I haven't tried to build a Melquiades but I understand tube electronics decently, so I'd like to comment on this problem.
The main question is why Domidaw's output tube is apparently carrying 3 to 4 times as much plate current as it should be. It is possible the tube is not being biased correctly, or is just a far-out-of-specification tube, but if it is carrying that much current (880 mA) then the tube should be overheating, showing red plates or just a ridiculous amount of heat coming off the tube. Even if the tube is internally shorted from plate to cathode, given the assumed current and measured plate voltage, the tube should be running perceptibly too hot.
If the tube is not running excessively hot then maybe it isn't really carrying all the current running through R22. Maybe C10 is shorted to ground and is carrying most of the current passing through R22. Domidaw should measure the voltage across the 1-ohm R21 to determine the current going to the output tube. If it is 0.88V then C10 is not shorted and the tube is really drawing excess current; if it is about 0.2V then the tube is drawing about 200 mA as it should, and C10 is shorting. If C10 is OK then a next thing to try would be replacing the output tube with another, preferably good-tested 6C33C.
I don't think the difference between 240V and 280V at the power transformer secondary could be the cause of such a large anomaly, and the transformer should not be tampered with until more is known about where all that current is going. Good luck,
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