2e24 DHT

 It was suggested to me recently by Piotr to explore the 2e24 after looking at the 2e22. This small directly heated pentode have about 10-12W of anode dissipation depending how it’s wired. I suspected this DHT in triode mode will have a high anode resistance so as soon as I managed to get hold of a sample, I submitted it to the mercy of my curve tracer:

Ra is on the range of directly heated pentodes wired in triode of similar size. Here is the triode model matching these curves:
Now let’s see how this little fellow will perform with a Zaa=6k5 load:

Not that great, probably will be better in Schade feedback:

Applying only 10% of feedback reduces the Ra to about 1k3 and the triode SPICE model still matches quite well the curves. So how will perform then with the same load?

We can see an improvement by applying Schade-like feedback. We can squeeze out about 1.5W @1.1% THD but paying the price of a higher H3 component in the mix. Interesting to see that the driving requirements are low (about 54Vpp).

A valve that could be driven by a simple MOSFET common-source stage and will make a very small and simple amplifying stage…

Author: Ale Moglia

"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp) View all posts by Ale Moglia