by Jac » Tue May 09, 2017 12:44 pm
Hello,
the way to use the V4 tubes is hopeflly described in the data sheet in such a way it makes sense to you, and you don't get stuck with a feeling not really knowing what this is.
The AN-06 is just interesting stuff for people who want to know details.
In short, you should just connect the cathode of the -V4 tubes the same way as you would connect the cathode of any indirectly heated tubes. The same way, there is no difference whatsoever. So you connect anode, grid, and cathode, and you are done.
What remains, is how to heat the -V4 tubes. Also that is not any different, with the only exception the heater supply of the -V4 must be floating. Whereas for indirectly heated tubes it can be floating or not.
Best is DC heating, so you have zero hum. The Tentlabs should be checked for exactly 5V on a warm tube. Then, the tube will divide that in 2.5 and 2.5V because the tap in the middle.
The issue with DC offset inside a DHT tube, can not be solved with any kind of DC heating. However there are no practical problems resulting from that. Alternatively you can use 50Hz AC heating, use ultrasonic heating, or subsonic heating like 20Hz. The thing you could do, is parallel the two heater halves of the 300B-XLS-V4 so you get a 2.5V 2.8 Ampere heater. That would reduce the DC offset, but it becomes a normal 4 pole DHT then, with no more cathode center tap. This can be done only for the 300B-XLS-V4.