I am running the plates pretty hot, max on the data sheet is 250v and I am at around 270.Hi All. The 12AX7 that came in the cb was a nice Amperex Holland so I left that in there, and I swapped the original Sylvania 6AQ5 with an old Tung-Sol I got in a bag of 6AQ5s from a junk shop for $10, this tube is cheap which I love. I was worried about noise, but it works awesome and doesn't even get hot, crazy these things only cost a buck or so. The heater output of the tranformer was 12v and I didn't have the right resistor combo to drop to 6v so I used a cheap ebay buck converter. I even reused the circuit board from the cb that holds the tubes, which I'm glad I did, but it likely made it even harder than point to point as the circuits weren't that similar. The only thing I bought was filter caps as I didn't have values that low. I will likely paint it and put it in my living room to play. The best part is I can crank it to 10 and still play it in my house. With the triode/pentode switch and nfb switch some very nice crunchy tones are also possible, which sound cool and I was not expecting it.
With settings close to the original champ it is beautiful and clean until 4 o'clock, then very nice overdriven tweed up to 10. I was not expecting much honestly sound-wise, especially with the output transformer so small, but I am blown away by how it sounds. I don't know this guy, but saw he had done something very cool in his circuit by adding a switch to run the 6AQ5 as either a pentode or a triode, so I added that too. Solid State Rectifiers, as the cb didn't use a tube rectifier and I didn't have one on handĪ 3 way switch for selecting either negative feedback, no negative feedback, or no feedback and adding a bypass cap to the cathode of the second preamp stageĪfter getting deeper into the project, I found a similar project called the "microchamp" in which someone had created a similar 6AQ5 amp, all awesome details here. I added hi/low inputs and a tone knob like on the 5f2a Princeton circuit seen here The final amp is pretty similar to the 5f1 champ circuit (seen here) but with a few modifications: I wanted to build something closer to a 5e3 Tweed Deluxe, but I was advised that even though the power transformer is large, it likely wasn't designed to handle 15 watts continuously, so I went for a much smaller 3 amp goal akin to the 5f1 Champ. The 6AQ5 is an output tube which is essentially a 6v6 in a small bottle. It had a number of tubes in it, but the main interest to start was the power transformer, the output stage for the cb which contained a 12AX7 and 6AQ5, and the output transformer which is quite small and outputs to a small 4 inch jensen speaker. The original cb was a International Crystal (more info here) tube cb. Improving my tube circuit knowledge was more important than necessarily the usability of the end product. The point of this exercise was for me to try to learn to not just depend on schematics, but be able to adjust things based on what I had. The goal was to try to only use parts from the cb, or parts I had laying around the garage. I put this little guitar amp together from the parts of a tube cb that I picked up for $20.
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