A forgotten Russian pentode
There’s not much information around the 6Ж49П-ДР or 6Z49P-DR / 6J49P-DR pentode. This pentode was designed for high-frequency operation and durability. It has relatively high transconductance and high mu when is triode connected. Hence, an interesting device for a phono stage given the low capacitances in place as well. The 6Z49P is close to his brothers 6Z51P and the famous 6Z52P albeit it has different characteristics.
I handpicked a sample from my stash which was close to the data sheet specs:
From the data sheet transfer curve above we can see that a test point can be chosen easily here:
- Ia = 22mA
The device under test here measures very close to spec, however it has a lower transconductance, nearly 55% less. If you look at the data sheet, you will notice that the transconductance at this point flats out, so it may explain the difference due to saturation effect:
It is interesting to see that anode resistance is about 60-65kΩ at this point. This info is not available in the data sheet.
Now if we trace this valve in triode mode, here is what we get:
The triode curves look very linear at first glance. Also the mu is high (about 50) and the anode resistance is around 3.5kΩ. Below is the Spice model fit:
The Spice model can be found here: 6Z49P-DR triode model. The capacitances aren’t correct as I couldn’t measure them in triode mode given lack of time. The model is pretty accurate in my view.
Now, what about the pentode Spice model?
I had to remove some data sets above due to the saturation effects. However, the model is accurate within the area of normal operation. Here is the pentode Spice model: 6Z49P-DR-PENTODE-VS150V.cir.
I’m sure this is a nice candidate to play around. Keen to read your experience with this valve if you have listened to it. Please send me your feedback if you can.