Megatron Electrostatic Headphone Amplifier

[Shawn]

Quick update:

it’s 6 AM here in California and I just wrapped up some late-night tweaking. Someone PM’d me earlier asking how I solved the offset and balance issue, and I can finally say: done. Offset is now around 0.3V and balance is about 0.2V.

If anyone else is running into similar issues, here’s what worked for me:

1.CCS Set Resistor: I kept the CCS set resistor at 1.5k, which gives around 22–23mA static current. You can try lowering to 1k if you want around 25mA, but I found 1.5k sufficient. The more plate current you have, the higher the offset you will get.

2.Cathode Resistor: Changed from 3300Ω to 7k–7.5k. A larger cathode resistor gives you a deeper grid voltage. I could only find suitable 7k wirewound resistors on Mouser – they’re a bit bulky but still fit. Note: Larger values will increase the offset, so some trial and error is expected.

3. Grid Pot: I replaced the 10k pot with a 50k, which gave me a much wider range to trim both offset and balance.

Final bias: around 24–25mA static current, Vgk ≈ -75V.

Hopefully, this helps anyone else dialing in the Megatron XL  and happy tweaking!😊

[JoaMat]

Glad you find a way to adjust the offset.

With EL34 as CCS, +400V and offset close to zero, I believe 1.5K gives ~23mA and 1.0K gives ~34mA.

Edited 4 hours ago by JoaMat