Hi, for some time I was playing with the idea of building a portable speaker with tubes. I normally build guitar amplifier, but this time I gave this a shot.
I posted the whole design and build process over instructables How to Build a Portable Bluetooth Tube Amplifier : 14 Steps (with Pictures) - Instructables, maybe you find it interesting.
And a picture from the interior:
For a low cost tube amplifier build it turned out pretty nice.
Cheers.
I posted the whole design and build process over instructables How to Build a Portable Bluetooth Tube Amplifier : 14 Steps (with Pictures) - Instructables, maybe you find it interesting.
And a picture from the interior:
For a low cost tube amplifier build it turned out pretty nice.
Cheers.
That is very nice. Mahogany has long been a favorite of mine.
Did you end up getting the anticipated 5,3 hours of operation per charge?
Seems like heat would build up inside, though.
Surely preparing that long, detailed Instructable was as much or more work as the build itself!
Good going, Regards
Did you end up getting the anticipated 5,3 hours of operation per charge?
Seems like heat would build up inside, though.
Surely preparing that long, detailed Instructable was as much or more work as the build itself!
Good going, Regards
I have not checked how much the battery lasts. Haven't had the time.
After one hour playing it was just a little warm, the 12A*7 creates much less heat than the EL84 or russian subminiatures (6n16B) with similar filament power.
And you are right, stopping to take the pictures and write everything down took a lot of time. I hope that so I may convince someone to build one too.
After one hour playing it was just a little warm, the 12A*7 creates much less heat than the EL84 or russian subminiatures (6n16B) with similar filament power.
And you are right, stopping to take the pictures and write everything down took a lot of time. I hope that so I may convince someone to build one too.
Thomasha,
Nice looking amplifier!
Edited: I missed the schematic the first time.
Now I can see it.
Thanks.
The EL84 filament takes 0.76A at 6.3V,
The 12AU7 takes 0.3A at 6.3V, less than 1/2 of the EL84.
Nice looking amplifier!
Edited: I missed the schematic the first time.
Now I can see it.
Thanks.
The EL84 filament takes 0.76A at 6.3V,
The 12AU7 takes 0.3A at 6.3V, less than 1/2 of the EL84.
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Nice looking - but seems pretty cramped inside - if you designed it from scratch might you make it a bit larger? What's the response curve like at the low-end?
Really nice! It makes me want to get off my butt and go into the garage and stop overthinking the things I want to make. Mahogany is such I nice wood to work with, soft, yet it holds together, and doesn't split easily and looks great. Nice job. A little more interior room would probably make for better bass, but for a kitchen or nightstand it's better than listening to a phone for sure.
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I have used 12au7's in a sealed box for a mixer with no problems.
Its only a watt or two so no more heat than a 2 watt resistor in the box.
I wanted it to be as small as possible, but you are right, more space would be better. I am planning something in the future using two 6ak6 tubes (only 150 mA filament) for a stereo amplifier. The extra transformer and tube will need more space.
I haven't checked the low end. It sounds good to me, but only a measurement can say how good. Unfortunately, my scope does not have the frequency sweep function, so that I will have to measure the output at some specific frequencies to have the response curve.
Yes, but isn't there more power being dissipated than just the tubes? An SMPS or two as well? ..😉
Sure is pretty, though ..
Cheers
Sure is pretty, though ..
Cheers
Yes, it also has one SMPS for the higher voltage, the lower voltage is obtained with a voltage regulator from the batteries. From both, the SMPS is what gets hotter. 240v from 12v to 16.8v input with the IRF644 (Rds on 0.28) surely will produce lots of heat.
The box, after one hour playing, was just warm near the SMPS, but not even as warm as a wi-fi router. But you are right, a better heat transfer would be nice. In a non-diy build I would probably use a metallic material for the back plate, so that it could dissipate the heat.
The box, after one hour playing, was just warm near the SMPS, but not even as warm as a wi-fi router. But you are right, a better heat transfer would be nice. In a non-diy build I would probably use a metallic material for the back plate, so that it could dissipate the heat.
Hi,
after some long time decided to measure the frequency response of the amplifier.
Input was a 30 mV signal ranging from 50 Hz to 20k Hz. I used Audacity as my signal generator and measured the RMS output with a scope. The voltage gain was then converted to dB, as plotted in the figure.
When injecting the signal directly through the input jack the gain drops drastically at higher frequencies. I have no Idea what could be causing this, other than the summing network at the front of the amp.
For the measurement with the bluetooth receiver I connected my notebook to the the receiver and sent the same signal, just adjusting the volume, so that if measured at the jack, where the signal is switched between input or bluetooth I obtain the same 30 mV for the first measurements. It resulted in a better frequency response, as can be seen in the figure.
Interesting is that it has an almost constant gain over a wide range of frequencies.
after some long time decided to measure the frequency response of the amplifier.
Input was a 30 mV signal ranging from 50 Hz to 20k Hz. I used Audacity as my signal generator and measured the RMS output with a scope. The voltage gain was then converted to dB, as plotted in the figure.
When injecting the signal directly through the input jack the gain drops drastically at higher frequencies. I have no Idea what could be causing this, other than the summing network at the front of the amp.
For the measurement with the bluetooth receiver I connected my notebook to the the receiver and sent the same signal, just adjusting the volume, so that if measured at the jack, where the signal is switched between input or bluetooth I obtain the same 30 mV for the first measurements. It resulted in a better frequency response, as can be seen in the figure.
Interesting is that it has an almost constant gain over a wide range of frequencies.