KT88 with chub clem

[Shannon Parks]

Here's one more shot, with 340 ohms (2x 680 ohm 3W resistors) and the adjusted B+ voltage. The extra losses in the power supply are a key part of the equation I had left out. Our current almost doubles versus a stock Clementine 6L6. The PA774 is 80 ohms DCR, the choke 55 ohms DCR and then there's the 100 ohm resistor at R21. All that multiplied by extra 100mA is another 23.5V drop in B+. Dissipation at R21 is now 4W, so that needs to be changed: maybe 50 ohms, another choke or even jumpered.

Shannon

[Ty_Bower]

This will prob yield a output @ ~8watts?

Keep in mind the TubeCAD SE software that Shannon is using to model the circuit is calculating a peak output voltage and using that to determine output power. All your math seems to suggest you are measuring an RMS voltage. In other words, the 4 watts RMS you've measured is the same as the 8 watts peak predicted by the model. Again I will say, you are not going to hear (or even measure) a significant difference by changing out your 670 ohm cathode resistance for 400 ohm. The difference in power output will be measured in tenths of a watt. Even replacing your output transformer with a 3.5K unit might get you close to 5 watt RMS (Shannon's last model), but I don't think that is what you are after.

Don't let me discourage you, though. Half the fun of this hobby is tinkering with the circuit and seeing what it does. It's a great way to learn.

[Ty_Bower]

The extra losses in the power supply are a key part of the equation I had left out.

Excellent point. As you bias the tube harder and draw more current, the power supply will only sag more. As the B+ drops, the output power drops even faster.

[justinsweber]

When we looked it seemed that 3.5k gave great distortion and less power. We had thought that a 5k would have been the better choice. Can you help int the sims?
I think tube can can show rms too?

Thank for all the detailed help. It shows how much work was put in on the back end.

[Shannon Parks]

Note that all my sim shots don't correlate with each other very closely due to the different output impedances and the lack of adjusting the earlier modelling for the extra voltage drop. Generally speaking, a lower impedance output will be more power and more distortion. Likewise, a higher impedance output will be less power and less distortion.

Shannon