I have this old tube line level preamp that someone built years ago and it sounds wonderful. I don't know who built - an audio friend of mine sold it to me claiming it was some prototype. I forget who he said did it. It uses 6 12AX7 tubes - 2 for the line level and 4 for the phono section.
Over the recent lockdown, I thought it would be fun to replicate the line level portion of the preamp so I could use it in an office system. I've built a few pieces of equipment over the years and this seemed simple enough.
It uses a 290V B+.
The schematic I drew in Kicad after carefully examining the existing circuit. I believe it is right. I've built the new circuit exactly the same as the existing circuit and yet I am running into a lack of gain. The preamp "works", there is very little noise, all the plate voltages test the same as the existing preamp. Anyone have any ideas? Thanks.
Over the recent lockdown, I thought it would be fun to replicate the line level portion of the preamp so I could use it in an office system. I've built a few pieces of equipment over the years and this seemed simple enough.
It uses a 290V B+.
The schematic I drew in Kicad after carefully examining the existing circuit. I believe it is right. I've built the new circuit exactly the same as the existing circuit and yet I am running into a lack of gain. The preamp "works", there is very little noise, all the plate voltages test the same as the existing preamp. Anyone have any ideas? Thanks.
Attachments
The second triode lacks it grid return resistor for DC, so, it will operate at random bias voltage, usually so high thet the tube is cutoff. There MUST be a grid leak return. 1 MΩ from pin 7 to chassis ground will be sufficient.
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