Well, all the data for the aforementioned optimization is collected and in the computer. I’ve been chewing on the data and my notes for the last couple of hours and it’s safe to say, there is a lot more here than first meets the eye.
Here’s how my desk looked when I just finished taking all the data.
Some of the data series were taken multiple times. This was simply because the data is such a departure from what I recorded during the 6V6 and 6L6 optimizations. Some looks mostly like I expected. For example, here is the top level plot of maximum RMS power out verses bias voltage for five different plate voltages.
These curves are not wildly unexpected but I would have expected the higher plate voltage curves to be more horizontal. However, some of the other series data for dissipations and harmonic distortion will take some time to get my head around.
The only conclusion I can comfortably draw right now is that the EL84 should never be operated at a plate voltage of 300V. I think a plate voltage of about 275v is the highest I would ever run this tube. The behavior at Vp=300v seems to indicate that the suppressor grid is not functioning properly at this plate voltage level.
I’ll have to chew on this entire data set for a while before I can begin to draw any firm conclusions, I may also try a few listening tests at various operating points as well. Just to see if some of my suspicions are borne out in the actual operation.
As always, questions and comments are welcome.