Hi, I'm interested in building a tube headphone amp, just to try. Being my first tube build, I think is better to work on low voltage, but instead of using starved tubes I want to use real low voltage ones. I can get 26A7GT tubes, that run on 26V, so they seem perfect.
My idea is a single ended amp to use with 32ohm Grado headphoner (99,8dB). So here are my questions to you:
- Output transformer: if I have made the maths right, I need a 1300ohm anode load. Datasheet says a 1500ohm, so it's not far away. Can I use a 500:8 transformer? The 32ohm will be seen as a 2000ohm load. Will it be right or is it too much? If I use the 250 terminal, the load will be 1000ohm.
- Biasing: being the voltage 26V, is it possible to use cathode biasing? The 28D7W datasheet states a cathode resistor to operate in class A, so I can suppose it's possible too with the 26A7GT.
What do you think? Thank you in advance.
My idea is a single ended amp to use with 32ohm Grado headphoner (99,8dB). So here are my questions to you:
- Output transformer: if I have made the maths right, I need a 1300ohm anode load. Datasheet says a 1500ohm, so it's not far away. Can I use a 500:8 transformer? The 32ohm will be seen as a 2000ohm load. Will it be right or is it too much? If I use the 250 terminal, the load will be 1000ohm.
- Biasing: being the voltage 26V, is it possible to use cathode biasing? The 28D7W datasheet states a cathode resistor to operate in class A, so I can suppose it's possible too with the 26A7GT.
What do you think? Thank you in advance.
1500 ohm x 3 times min. = 4500 ohms OPT to avoid poor bass due to the low inductance of OPT
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Ok, I understand. Then I can use the 1K terminal of the OT, obtaining 4000 ohms, which it will be better than my previous idea.
Oh, I forgot I have a Mullard EL504 somewhere (I had the idea of making a simple low wattage guitar amp). Looking for information about low voltage tubes, I've read that it is a tube that can work well at ~50V, drawing quite enough current. It would be an alternative, but I don't like the unusual anode connector. But I see it's an available tube in the market.
Thank you
Oh, I forgot I have a Mullard EL504 somewhere (I had the idea of making a simple low wattage guitar amp). Looking for information about low voltage tubes, I've read that it is a tube that can work well at ~50V, drawing quite enough current. It would be an alternative, but I don't like the unusual anode connector. But I see it's an available tube in the market.
Thank you