Testing an El84 Vacuum Tube with 9v Batteries

I have always been interested in vacuum tube amplifiers, however the high voltages from the mains has always kept me from experimenting with them. About a year ago I played with an low power tube the 1t4 in a regenerative receiver. The B+ was set to 45V powered from an array of 9v batteries. I decided to revisit an old guitar amplifier project I started in high school using an EL84 power pentode.

The first part was to figure out a way to mount the tube so I could experiment with it. I found an small metal box that worked well for mounting the tube socket. I then took some wires from a broken ATX power supply and soldered them to the tube socket.

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After I had everything assembled I brought it to the test bench and wired up the test circuit below. I measured the current at the anode versus the voltage at the gate. I kept adding 9v batters to the B+ supply and noted the results.

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Below are the results I noted along with a graph. I also included the triode configuration graph from the original datasheet.

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So far the data looks consistent with the original datasheet for the tube in triode mode. The tube can sink a lot more current when VG2 is around 350V running in the full pentode configuration. Even with all 12 9V batteries I might be able to drive about 1watt of audio to a speaker. I was also surprised that the heater alone took around .7 amps at 6.3V. This is definitely not the most efficient way to drive a speaker I hope to get an proper impedance matching transformer so I can hear how it performers soon.

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