I have recently been playing with low voltage tubes. I am not talking about using tubes that were ment for high voltage with low voltage. I am talking about tubes that were made to be used with low voltages. In the end of the tube life cycle, a bunch of tubes were designed to run on a car's 12V battery. These tubes were used in car radios. I have made a simple single ended tube amp running on a single 12V wallwart!
The key to producing a somewhat decent volume is to use the following:
- 12U7, it's a medium dual triode very similar to a 12AU7
- 12K5 power tetrode as the power tube. This can apparently yield close to a 1/4 watt on 12V
- A small output transformer (i.e. 600 ohm to 8 ohm Hammond's 119DA is the one that I am using, I think that the cheap radio shack 1k to 8ohm might be allright, although, it will not be as loud)
- A wallwart with about 1.5 Amps output @ 12V (the tubes heaters take .75 Amps!)
All of these things are easily available at http://www.tubesandmore.com
This produces a surprisingly loud volume for tubes running on 12V!!! Don't expect ear piercing volumes or mega gain like a soldano. This is simply a start of a way to safely experiment with tubes without fearing to be killed because I touched the wrong wire.
My goal was to produce a quality tube amp that can be used in a home setting (low volume) with low voltage (makes it safe to experiment with).
I want to experiment with another tube at 12V (a pentode, 12CX6) before moving up to 24V (the tubes have a maximum plate voltage of 30V)! There are a lot more designs that I want to try out! Since it's low voltage, it's very easy to play around with it, we can simply breadboard it (unlike high voltage stuff, I wouldn't want to breadboard stuff running at 300V!!!!!!).
Simply amazing little tubes they are.
Here is the schematic:http://www.geocities.com/slajeunesse/low-volume.html
To pins for the heaters aren't showed on the schematic. Here is how the heaters are connected:This was edited:
For the 12U7:
- Pin 4 gets 12V
- Pin 5 goes to ground
- Pin 9 is not connected to anything
For the 12K5:
- Pin 3 gets 12V
- Pin 4 goes to ground
Make sure that the power supply is well filtered and regulated (see the ruby tuby schematic for a power supply with filtering and regulation http://www.geocities.com/slajeunesse/ruby_tuby.html
Here are the links for the pinouts for the two tubes that I am using:http://tdsl.duncanamps.com/show.php?des=12U7http://tdsl.duncanamps.com/show.php?des=12K5