headphone amplifier 6418 sub-miniature tube preamp

We often get questions asking about suitable vacuum tube (valve) kits for beginners or first time DIYers. Aside from the fact that vacuum tube audio kits are generally expensive, there is also the safety concern that most tube circuits operate with potentially lethal voltages. Mark in Australia found the following 6418 tube preamplifier and headphone amp kit which is an exception - it is inexpensive and can operate from single 9V battery.


The tube preamp / headamp kit is from Oatley Electronics in New South Wales Australia and based around the Raytheon JAN6418 sub-miniature valve (tube) and an IC. The K272 Stereo Tube Preamplifier – Headphone Driver kit cost $27AU (~$23US – August 2009). The kit is complete including a printed circuit board (PCB) which makes for easy assembly but you will need to provide your own enclosure. The kit only consumes about 12mA at 9V and can be powered with a single 9V battery making this a safe and ideal kit for those who are new to vacuum tube electronics.


The photo above is a build of the kit using the supplied parts. Since the 6418 tube are extremely microphonic and will "ring" if they are subjected to vibrations rubber grommets are used to help damp the tubes. Mark has built a number of these kits now including a few with upgraded parts (metal film resistors, polypropylene film inter-stage capacitors and a Burr-Brown OPA2134 op-amp). The photo below is a tube preamp in a plastic ABS enclosure using the kit and upgraded components.


Mark reports that the kit performs well and sounds good. The bandwidth is very wide, the -3dB points are 10Hz and 50kHz. As a preamp there is good depth, wide breadth and sharp detail revealing fine recorded detail with no hard edges. The photo below shows the kit in a plastic enclosure being used as a portable headphone amplifier.