Hi Nick,
Yes the extra triode does give more gain, a bit more, I can see that but what confuses me is that I can't get it to give anywhere the same level of gain as a bypassed cathode, assuming the same load, (or diodes in this case) on the straight forward pentode stage.
Now, it does indeed look more linear and that could well a be very worthwhile improvement but it looks to me like there's still quite a bit of degenerative feedback at the cathode.
cheers,
-- Andrew
Possibly a silly idea
#17
Oh, you are right, there isn't that much in the gain difference, I had forgot to adjust the B+ when using a 10k for the pentode. duh.
Maybe half a dB difference, so no big deal.
But over 6dB difference in the level of 2nd harmonic, so thats worthwhile, so maybe the idea has some merit in terms of lower distortion. That was the original though, by providing the pentode with a almost constant voltage on its anode I hoped the distortion would be lower. It was just a question if the extra triode would add more distortion than it was removing. 1.36% for the single pentode, 0.57% for the two valves.
Though a d3a as triode with a CCS load is better still.
Maybe half a dB difference, so no big deal.
But over 6dB difference in the level of 2nd harmonic, so thats worthwhile, so maybe the idea has some merit in terms of lower distortion. That was the original though, by providing the pentode with a almost constant voltage on its anode I hoped the distortion would be lower. It was just a question if the extra triode would add more distortion than it was removing. 1.36% for the single pentode, 0.57% for the two valves.
Though a d3a as triode with a CCS load is better still.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.