Hi
This amp had its rectifier tube 5AR4 shorted. I replaced it with a new JJ,GZ34S tube. I wanted to measure it tube dissipation, 4 EL84 power tubes. I set the bias setting at "warm". One side DC resistance is 76 ohms and the other is 75.8 ohms. The voltage drop on each side is about 5.1V and the cathode to plate voltage is approx 341V. This means each side dissipates 67mA which is approx 22.9 Watts. Total of 45.8 Watts. I read that this amp is rated 30W. This amp is fixed bias, either at "warm" or "hot". Do you think that something is wrong with the bias circuitry or is it set as such. I could not upload the schematic as it 1.94MB
Thanks
This amp had its rectifier tube 5AR4 shorted. I replaced it with a new JJ,GZ34S tube. I wanted to measure it tube dissipation, 4 EL84 power tubes. I set the bias setting at "warm". One side DC resistance is 76 ohms and the other is 75.8 ohms. The voltage drop on each side is about 5.1V and the cathode to plate voltage is approx 341V. This means each side dissipates 67mA which is approx 22.9 Watts. Total of 45.8 Watts. I read that this amp is rated 30W. This amp is fixed bias, either at "warm" or "hot". Do you think that something is wrong with the bias circuitry or is it set as such. I could not upload the schematic as it 1.94MB
Thanks
If an amp is rated for 30 Watt, it means that it's maximum audio output power is (about) 30 Watt. That's something different than the dissipation of the anodes. Although biased hot, the anode of an EL84 can stand 12 Watt, so you are still under that limit. With input signal, the avarage dissipation of the EL84's goes down, because part of that power is converted in audio power through the OPT.
Did you also measure in the "hot" position?
Did you also measure in the "hot" position?
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tip: don't use the standby switch on this amp. Leave it on the on position! Bad design will eat rectifiers.