Now that the Source Selection Preamp writeup is complete, I took a little time today to prepare for another effort.
Here is the unit on which I was working.
Astute readers will recognize this as the jig I built to perform the 6L6 UL Optimization study. However, it’s undergone a little change.
This jig was originally built to work with power pentodes with 7AC and similar base pinouts. These include the 6L6, 6V6, 6W6, 6Y6, and similar tubes. In the 7AC pinout, pin 1 can be either an internal shield or not connected. So on the jig I left pin 1 open. But for this new project I need something different.
I want to start work with an EL34/6AC7 power tube. The EL34 has a 8ET pinout which is virtually identical to the 7AC with one exception. In the 8ET pinout, the suppressor grid is not directly tied to the cathode (as in the 7AC) but is instead brought out to pin 1. So the addition is this little switch.
With the switch in the 6L6 position, pint 1 is left open. In the EL34 position, pin 1 is tied to pin 8 (i.e. the cathode connection) which is the way EL34s are generally run in audio frequency power amplifiers.
Now I just need to start reviewing data sheets and curve families to see where I want to start with this new optimization study. I publish more as I proceed.
As always, questions and comments are welcome.