Feed a power triode directly with another power triode and you will have a dynamically coupled output. Okay, so dynamically coupled is fancy for direct coupled, but that doesn’t mean the concept isn’t cool. I once built a guitar amp using this method and it sounded surprisingly aggressive when driven fully, yet just what you’d expect from a triode for the clean. Let’s build a dynamically coupled amplifier.
Take a glance at the link below and you’ll see this idea was around in 1935. this 6B5 tube was developed to give us value in power out and fidelity (6N6 is another option). Best of all it contains both triodes needed! We don’t even need to bias this tube, so basically all the design work is done for us.
https://frank.pocnet.net/sheets/201/6/6B5.pdf
https://frank.pocnet.net/sheets/127/6/6B5.pdf
Hook up the heater, ground the cathode, and add the B+. This is ridiculously simply, and we have a good foundation for a HIFI or guitar amp. We need 17 volts to drive this amp, so we can just use any typical 2 stage preamp design. Only 5% total harmonic distortion at 5.2 Watts out. This thing is looking pretty, but we can make it even better with our own preamp design and some inverse feedback to increase fidelity. Links below to design your own preamp, and calculate a feedback resistor.
https://crunchytubeamps.com/use-the-preamp-tube-of-your-choice/ https://crunchytubeamps.com/improving-your-budget-amp-build/
I went with two 6F5 tubes to drive my dynamically coupled 6B5 tube. Using the exact set up from the design your own preamp link. I paired this circuit with a 5V4 rectifier tube. Why? because I have two of them. IMO tubes all have the same basic sound, but they all have fringe differences. I can’t put my finger on it, but a dynamically coupled power output is just different enough to be worth a build.
Output Transformer option
