Cathode was connected to ground.
Anode through an output transformer to Vb. The transformer is a 5KΩ to 600Ω or 4Ω. The speaker connected a few inch full range.
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The input signal from the line out of a Sony portable CD player was coupled to the grid through 1 μF.
There was no sound. Connecting a 10MΩ from grid to ground or cathode still no sound.
When a 10 MΩ resistor was connected from anode to grid, sound started coming out but very low and distorted. If memory is correct a 5 MΩ was tried too with not much improvement. It cannot be recalled if a 1MΩ was tried.
Vb was changed from 6V to 12V. There was 3x improvement but still the result is unusable.
It was found strange that if the grid voltage was monitored it was steady at 5V. It did not drop to - mV when the cathode was heated as it happens on the EF183. This indicated the grid could not attract electrons through the Rag otherwise there would have been a voltage drop from the current flowing through 10MΩ. Is there a voltage threshold? Should a higher voltage be carefully tried? (The tube was checked to operate properly on a Dansette record player).
The EL84 was substituted by the EF183, triode connected. The EF183 allows connection of the suppressor grid to the anode. It is a vary μ, high gm electron tube. There was dramatic improvement. See the next euroelectron post.
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