Hi Andy, thanks for the offer. Will think about that.
As an update, I grafted half a 6SN7 in between the 76 and 2A3, that made it two stage. While I think I'm getting some 6SN7 coloration, the 76 tone is still prominent.
The bass? Well, I got it! And better than expected.
I'm happy with the circuit now. Maybe in another chassis I'll make a 76-76-2A3/45.
As an update, I grafted half a 6SN7 in between the 76 and 2A3, that made it two stage. While I think I'm getting some 6SN7 coloration, the 76 tone is still prominent.
The bass? Well, I got it! And better than expected.
I'm happy with the circuit now. Maybe in another chassis I'll make a 76-76-2A3/45.
When using the LED bias at low currents its very easy to add supplementary current to the LED. I did this with rectified heater supply passed to a LM7805 and then a simple bypassed voltage divider. Before adding the supplementary current, things sounded soft and mushy, with it things tightened up significantly.
Something I noticed this week when I switched from a 65R cathode resistor with supplementary current, I had a bias point of 1.2V and 90V on the anode. I then replaced the resistor with a red LED, the bias moved to 1.6V but the anode stayed at 90V. There must be some DC feedback thing going on here. The point is - when switching don't expect things to pan out exactly as anticipated.
Shoog
Something I noticed this week when I switched from a 65R cathode resistor with supplementary current, I had a bias point of 1.2V and 90V on the anode. I then replaced the resistor with a red LED, the bias moved to 1.6V but the anode stayed at 90V. There must be some DC feedback thing going on here. The point is - when switching don't expect things to pan out exactly as anticipated.
Shoog
Point well taken Shoog. I have to admit, I haven't been able to add the supplementary current method yet. The reason is that I felt I needed more gain, thus the "jump" to a second stage.
Hi FranStar, thank you for the extensive post. In summary, I will try putting in a 33K resistor in series with the grid, and will sandwich the coupling cap with 5.6K and 15K resistor.
I will continue with the experiments.
Hi FranStar, thank you for the extensive post. In summary, I will try putting in a 33K resistor in series with the grid, and will sandwich the coupling cap with 5.6K and 15K resistor.
I will continue with the experiments.
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