DKJones96
100+ Head-Fier
- Joined
- Nov 25, 2008
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It has been a while since I was a regular here but I haven't forgotten about my love of small amps. Wanting a small amplifier for work I decided to get on a project that I had put off for a long time and I'm extremely pleased with the results.
The 12AE7 is, for all intents and purposes, a forgotten tube. It has but two schematics to its name in an automotive application(which are the same schematic) and was in use for 1 year before a transistor took its spot. It was a preamp and solid state output driver tube for an automotive radio and thus was designed to take 12V on the plate and 12V on the heater. Triode 1 is a medium-mu triode rated at a whooping 2mA and triode 2 is a low-mu triode rated to 13mA. The datasheets for it contain no curves and finding a schematic using this tube you have two choices, mine and the single factory application.
The amplifier is setup as a gain stage with a bootstrapped cathode follower which is fed via DC coupling to a BUF634(or in my case a 'Monofied Sijosae Discrete BUF634'). The first iteration used an output transformer and while it 'worked' it was far from ideal and didn't get nearly loud enough so I buffered the output. It is DC coupled throughout so it only has two capacitors in the signal path, one at the front end and one at the back-end.
It is surprisingly loud and measures fairly well at Noise Level: -102dB Frequency Response: -1.4dB 20-20,000Hz THD: 5% at 100mW. Wont blow your ears off, but sounds great! These measurements were taken on breadboard, I haven't done new ones in the completed form because I'm not quite done yet.
The schematic as-built.
Running on the breadboard!
Close, but not quite done. Some hum and hiss issues I had on the breadboard went away with the PCB version.
Sorry I don't have a PCB for this, if there is enough interest I could throw something together unless someone else wants to take a stab at it. I'd gladly buy a PCB.
I will update this thread with the final amplifier when I'm done. I integrated a stand-by relay so the rear switch turns off everything and the front switch on the volume control will cut power to the anodes and buffers and connects the heaters in series. Not hot enough to make them glow but it is instant-on.
The 12AE7 is, for all intents and purposes, a forgotten tube. It has but two schematics to its name in an automotive application(which are the same schematic) and was in use for 1 year before a transistor took its spot. It was a preamp and solid state output driver tube for an automotive radio and thus was designed to take 12V on the plate and 12V on the heater. Triode 1 is a medium-mu triode rated at a whooping 2mA and triode 2 is a low-mu triode rated to 13mA. The datasheets for it contain no curves and finding a schematic using this tube you have two choices, mine and the single factory application.
The amplifier is setup as a gain stage with a bootstrapped cathode follower which is fed via DC coupling to a BUF634(or in my case a 'Monofied Sijosae Discrete BUF634'). The first iteration used an output transformer and while it 'worked' it was far from ideal and didn't get nearly loud enough so I buffered the output. It is DC coupled throughout so it only has two capacitors in the signal path, one at the front end and one at the back-end.
It is surprisingly loud and measures fairly well at Noise Level: -102dB Frequency Response: -1.4dB 20-20,000Hz THD: 5% at 100mW. Wont blow your ears off, but sounds great! These measurements were taken on breadboard, I haven't done new ones in the completed form because I'm not quite done yet.
The schematic as-built.
Running on the breadboard!
Close, but not quite done. Some hum and hiss issues I had on the breadboard went away with the PCB version.
Sorry I don't have a PCB for this, if there is enough interest I could throw something together unless someone else wants to take a stab at it. I'd gladly buy a PCB.
I will update this thread with the final amplifier when I'm done. I integrated a stand-by relay so the rear switch turns off everything and the front switch on the volume control will cut power to the anodes and buffers and connects the heaters in series. Not hot enough to make them glow but it is instant-on.
