Tag: 12P17L

THD benchmark

I’m still in the process of testing valves, here is how the ranking is coming up so far. This is a mix of driver and output valves. All tested at Vo=+22.22dBu:

THD analysis of different valves

Looking at the chart above a couple of interesting points to highlight:

  • 4P1L is the most linear valve I’ve found so far.
  • 6e5P and 6C45 are expected to be on the top five anyway.
  • 12P17L despite of having similar characteristics as 4P1L is not that linear
  • 6N6P and 6N6P-I disappointed me. I thought the would be more linear..
  • 46 and 47 in triode mode are superb drivers

Have so many other ones to test, but limited time….

Expect this chart to be updated in the future, so stay tuned 🙂

12P17L THD analysis

THD analysis for 12P17L in triode-mode (left-handed)

Looking at the THD for the 12P17L in triode mode (left-handed) using a CCS load and driving the input with the TEST SET oscillator to achieve the output at 10Vrms (+22.22dBu) to look at valve’s distortion in particular.   This valve is more linear at lower currents (Ia=25mA) rather than an operating point to maximise anode power (e.g. Ia=50mA) as would be in an output stage:

THD @ Ia=50mA

Interesting to see that there is a point where there is a second harmonic cancellation and only H3 component is visible achieving very low THD (circa 1.3%):

Minimum distortion (H2 cancellation)
THD analysis

A compromise point to obtain maximum output power whilst minimising distortion was found to be:

  • Ia=35mA
  • Vg=-15.2V
  • Va=241V
  • THD=0.13%

This puts the valve under 8.4W anode dissipation. Looking at the specs you can see that anode dissipation is 7.5W and g2 dissipation is 2W.

12P17L THD at maximum output power

I’d rather operate this valve at a lower dissipation point.

12P17L curves and Spice model

A great russian pentode valve similar to 4P1L, but with indirectly heated cathode. You can check the valve specifications here.

I tested transconductance in left-handed triode mode: Gm=9.6mA/V @ Va=150V, Ia=50mA , Vg=-5.6V.

Here are the curves for this valve:

12P17L triode curves

For the ones who want to test the SPICE model here is my take on it:

You can try the model and please let me know your results! You can always email me