With a number of members working on some version of this amp -- either by way of circuit, use of Fisher transformers, or just that it's a 6BQ5/7189 amp, I thought I would mark my progress on my own version of this great amp.
I had mentioned the basic features in a thread kpaxfaq started for his build, but started a separate thread so as not to trample on his. And while the goal is to build a worthy copy of the Fisher product, my build contains enough "deviations" as it were to possibly appeal to a broader group, so I've posted the thread here -- but the moderators can decide as they will which forum it is best suited for.
The basic features include:
1. Fisher X-101ST power transformer and AC power cord from same (the latter to ensure authentic Fisher sound).
2. Retains GZ34 rectification (as used by the X-101), with adequate choke and capacitance filtering to handle the full power needs of both channels at once.
3. Revised tube lineup, using a 6FQ7 inverter and ECC83 input stage for improved inverter drive, and elimination of 7247 issues. Both tubes obviously handle both channels.
4. Heath AA-100 OPTs to produce performance at least equal to the original devices.
5. Application of EFB(tm) to a pentode output stage for bias, featuring traditional bias/balance adjustments for both channels using only one EFB regulator.
6. Extending the EFB concept (simplicity, with superior regulation that automatically adjusts to prevailing conditions) to power the screen grids, with the added benefit of eliminating the space heater capabilities of the original design.
The goal is to not only meet, but with the application of EFB II (for pentode operation), improved on the performance of the original design, while still retaining that wonderful 6BQ5/7189 sound.
The pics show the mechanical progress. From left:
1. Getting the layout right. Planning is everything.
2. Measure twice, cut once.
3. Just like a classic kit, layout the parts (mechanical only at this point) to make sure they're all there (tubes are dummies for show).
4. Everything mounted up ready for wiring.
5. The Principle Engineer (Banditt), simply exhausted from all the details of the project.
This will ultimately end up in a new article detailing the build, and spotlighting operation of EFB II, that is to be published on the Tronola website later this year -- but for now, I thought it would be neat to share the development process of the project with AK.
Family is in town this week, so the start of wiring will be delayed. I'll update the thread as progress continues......
Have a safe holiday --
Dave
I had mentioned the basic features in a thread kpaxfaq started for his build, but started a separate thread so as not to trample on his. And while the goal is to build a worthy copy of the Fisher product, my build contains enough "deviations" as it were to possibly appeal to a broader group, so I've posted the thread here -- but the moderators can decide as they will which forum it is best suited for.
The basic features include:
1. Fisher X-101ST power transformer and AC power cord from same (the latter to ensure authentic Fisher sound).
2. Retains GZ34 rectification (as used by the X-101), with adequate choke and capacitance filtering to handle the full power needs of both channels at once.
3. Revised tube lineup, using a 6FQ7 inverter and ECC83 input stage for improved inverter drive, and elimination of 7247 issues. Both tubes obviously handle both channels.
4. Heath AA-100 OPTs to produce performance at least equal to the original devices.
5. Application of EFB(tm) to a pentode output stage for bias, featuring traditional bias/balance adjustments for both channels using only one EFB regulator.
6. Extending the EFB concept (simplicity, with superior regulation that automatically adjusts to prevailing conditions) to power the screen grids, with the added benefit of eliminating the space heater capabilities of the original design.
The goal is to not only meet, but with the application of EFB II (for pentode operation), improved on the performance of the original design, while still retaining that wonderful 6BQ5/7189 sound.
The pics show the mechanical progress. From left:
1. Getting the layout right. Planning is everything.
2. Measure twice, cut once.
3. Just like a classic kit, layout the parts (mechanical only at this point) to make sure they're all there (tubes are dummies for show).
4. Everything mounted up ready for wiring.
5. The Principle Engineer (Banditt), simply exhausted from all the details of the project.
This will ultimately end up in a new article detailing the build, and spotlighting operation of EFB II, that is to be published on the Tronola website later this year -- but for now, I thought it would be neat to share the development process of the project with AK.
Family is in town this week, so the start of wiring will be delayed. I'll update the thread as progress continues......
Have a safe holiday --
Dave
