When we took the challenge to build a low power amp, we did a lot of research to see what others had done and what was commercially available.
We wanted an amp that had both low and high gain but still not too loud.
We considered a simple low power amp with a VRM. The VRM complicates things.
We wanted the iron and parts to not be expensive, the amp needed to be compact and small so it is still a budget amp.
We wanted to minimize controls so initially, tone control would be by the guitar tone.
Printed Circuit Board manufacture (PCB) needed to be an option.
We wanted to make it in a new Amp Camp because so many people have been asking for a camp. The Tramp was excellent but a lot to complete in a weekend. the TriFly would need to be built in a day.
We wanted to use a traditional owner supply and not a switch mode supply with complicated circuitry.
We wanted to use readily available off the shelf tubes 12AX7s and the family.
We had read about the Self Split design which eliminates the need for a Phase Inverter (PI) but less efficient than a true Push-Pull design that may help meet our goal of lower power and simplicity. It was invented by Phillips many years ago and was used in some budget amps of the day.
Self-split is a PP arrangement where the power tubes also function as their own PI. It's like cathode bias, but you leave the cathode bypass cap off, and the first tube drives the second one through the common cathode connection.
Link to Self Split Info
http://dalmura.com.au/projects/Valve%20Info.phpWe had the Hammond iron for a Firefly so that seemed like a reasonable starting point given it's immense popularity and it's public domain design. Plus we had some old 12AU7 and 12BH7 and a new ECC99 so the "power tube" wasn't a problem.
With all these criteria we began our build!
Login
Register
FAQ
Search
