Tag: 45 SE A2

Driving the 45 in A2 (Part 3)

Ok, the previous operating point wasn’t optimal from a musicality perspective. As suggested by 45, I reworked the load line for 36mA/275V and anode load of 5.6KΩ (which is what I could get with my OT):

45 loadline A2 version 3The driver should now provide V{}_{gk (pp)} = 2 \cdot (+20V + 55V) = 150Vpp.

The output power will be around:

P{}_{a}=\frac{1}{2}\cdot i{}_{ap}^2 \cdot Z{}_{a} = \frac{1}{2} \cdot (36mA)^2 \cdot 5.6K\Omega \cong 3.6W

Efficiency would be around 36% in theory. Happy if around 3W can be obtained from this valve here with a reasonable distortion…

 

Driving the 45 in A2 (part 2)

On the previous post I explored how more power could be extracted from the 45 in class A2. Here is a first draft circuit using the 4P1L as the driver stage with a mu-follower gyrator load to provide current with low output impedance:

45 SE Class A2 dc-coupled

3.5W can be obtained with 13Vpp input signal. Clearly a pre-amp is required, but that is the output level I’m currently getting from my preamp so should be fine. The LND150 CCS reference can be optimised and derived from the stable 280V.

Not a bad idea, just an additional power supply to avoid any nasty cap in the path.