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In the Forum: Melquiades Amplifier
In the Thread: R22
Post Subject: Plate currentPosted by JJ Triode on: 1/2/2022
Domidaw seems to be saying he has only one channel almost working, this one with the burning resistor. I don't think he said he has one (other) channel working correctly. If he is really dropping 240 - 196 = 44V across 50 ohms, then he has 44/50 = 0.88A flowing through R22, as Anthony said. If some of this DC current is not shorting through C10 to ground as I suspected, then it all has to flow through R21, TR4 and V4 in series; there is nowhere else for it to go. This would gives a plate current of 880 mA through V4, resulting in 170 watts plate dissipation given the plate voltage of 194V. The rated maximum dissipation for that tube (both plates in use) is 90 W. According to the schematic the dissipation in V4 should be 40-56 watts. I see only three possibilities:
1. Domidaw is mistaken about the resistance of R22, the voltage across it or both, such that the current is not close to 0.88A (but then why is it burning?)
2. Some DC current is shorting through C10 to ground, hence C10 is defective and should be replaced.
3. The tube is really carrying 0.88A current, indicating the tube is defective or wired wrong, or maybe there is a strand of wire or solder or something shorting the socket.
The current through R2 has to go somewhere, and it can only go through C10 or eventually V4. It can't just disappear.Rerurn to Romy the Cat's Site