Tag Archives: 12ax7

The baby is asleep, and the 6W tube amp is quiet…

It’s 12:11am, August 12, 2010, and I just gave up doing my College Physics to replace the first stage preamp cathode bypass resistor as noted in V1.3 schematic. I sure wish it wasn’t half past midnight :). I have it on 10° or less volume, and 45° EQ, give or take a degree. I’m just guessing. I really want to crank it up to see if the tone and distortion sounds better. 9-6-2010 – It does need some circuit tweaking. It doesn’t sound good to me after all.
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Tube Amp Build #2 Part 3 (Real-World Testing)

Today, 6-20-2010, I took the amp to church to test it out in the real world. My main concern was the heat from the LM317 TO-220′s. I used the chassis as the heat sink because without a large heat sink, the LM317′s would go into thermal shutdown which caused the heaters to drop out, which effectively makes the amp stop working.

My goal was to get at least 1 hour of continuous use. I played the amp from 7:45am to 8:45am, 10:30am to 11:30am, and 4:45pm to 6:35pm. The amp was very hot, but never cut out. This is good news.
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Tube Amp Build #2 Part 2 (The Circuit Design)

This amp has gone through quite a few changes. The reading might be interesting to see why I made certain choices, but the schematics here are for reference ONLY. They work, but they need work. Check on my tube amp page for the latest schematics.

[Brackets note changes and experiences after real-world testing had begun. Some things had to be ironed out during the perfection/acceptance process.]

Designing a tube amp circuit isn’t really that difficult, but it can be frustrating. The hardest part that I experienced was designing the output stage. I never really read anything that helped me understand why I did what I did. I’ll explain this when we get there. Also note that everything is designed to be within 10% of the expected value. Some things could be changed after other values are figured, but with tolerances of components falling between 5% and 25%, what’s the point in trying to get any closer on paper? Testing the actual circuit is the only true measure of its performance.
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