Using 2x ECC83S Instead of 6AN8 in Dynaco Mark III – Advice Needed
Hello everyone,
I'm currently building a Dynaco Mark III-style mono tube amplifier and I'm planning to replace the original 6AN8 driver tube with 2x ECC83S (12AX7) tubes for each channel. I understand this involves redesigning the driver and phase splitter stages to suit the dual-triode layout of the ECC83S.
My main question is:
Has anyone successfully implemented this conversion, and are there any confirmed, working schematic adaptations you could share?
I want to be absolutely sure before committing to this layout and buying tubes. Any practical experience, schematics, or advice on wiring, gain structure, or tonal results would be very much appreciated.
Thanks in advance for your help!
Hello everyone,
I'm currently building a Dynaco Mark III-style mono tube amplifier and I'm planning to replace the original 6AN8 driver tube with 2x ECC83S (12AX7) tubes for each channel. I understand this involves redesigning the driver and phase splitter stages to suit the dual-triode layout of the ECC83S.
My main question is:
Has anyone successfully implemented this conversion, and are there any confirmed, working schematic adaptations you could share?
I want to be absolutely sure before committing to this layout and buying tubes. Any practical experience, schematics, or advice on wiring, gain structure, or tonal results would be very much appreciated.
Thanks in advance for your help!
Last edited by a moderator:
Those tubes are not interchangeable, electrically or mechanically, and the gains are different, which affects the feedback network design.
Most would want to breadboard and test the various proposed circuits before making a decision on which one of them to use, if any.
Also, what works for one person may not work for you, in your system.
Most would want to breadboard and test the various proposed circuits before making a decision on which one of them to use, if any.
Also, what works for one person may not work for you, in your system.
Thank you for the input — much appreciated!
I completely agree: the ECC83S and 6AN8 are very different tubes in both internal structure and characteristics. I'm aware that this change requires redesigning the feedback loop and phase splitter, not just a tube swap.
I’m not trying to drop in ECC83S directly — rather, I’m planning a full rework of the driver stage using two ECC83S tubes per channel. My goal is to retain the output stage with KT88s, and power supply based on GZ34, while modernizing the input and phase inverter with tubes that are more easily available here.
I've already started adapting the schematic to reflect this, and I’ll be happy to breadboard and test as suggested.
Still, if you or anyone else has working examples of ECC83S-based driver stages that are known to work well with KT88s in push-pull AB1, I’d be grateful for any tips or references.
Thanks again!
I completely agree: the ECC83S and 6AN8 are very different tubes in both internal structure and characteristics. I'm aware that this change requires redesigning the feedback loop and phase splitter, not just a tube swap.
I’m not trying to drop in ECC83S directly — rather, I’m planning a full rework of the driver stage using two ECC83S tubes per channel. My goal is to retain the output stage with KT88s, and power supply based on GZ34, while modernizing the input and phase inverter with tubes that are more easily available here.
I've already started adapting the schematic to reflect this, and I’ll be happy to breadboard and test as suggested.
Still, if you or anyone else has working examples of ECC83S-based driver stages that are known to work well with KT88s in push-pull AB1, I’d be grateful for any tips or references.
Thanks again!
For an example, here's an early circuit for a different amp that Haler used before adopting the pentode input stage.
https://www.bonavolta.ch/hobby/en/audio/6l6_2.htm
https://www.bonavolta.ch/hobby/en/audio/6l6_2.htm