Having a small Hammond power tranni and three 6H3N triodes on hand I was looking for a build. Usually my headphone tube amps are based on the 6AS7 twin triode tube as power tube and 12AU7 as driver. But I stumbled on a schematic I had had for some years and it used two triodes in a HP amp. The backend is a White SRPP know for low output impedance. This HP amp was not designed for 6H3Ns but with some tweaking I could make it work. After the build voltages and biases were way out and it took four days of head scratching and tweaking to get it all balanced. Fortunately as a preamp or HP amp it is really excellent. Not sure why there isn't more designs around this inexpensive great sounding double triode.
The chassis is cast Al with Ocean Blue Hammertone epoxy enamel double coat. All wiring is P2P or Component-2-component and hookup wire is mostly fine copper wire with a silver plate. Not shielded wire is used. The PS is triple Pi with 300uf of caps (CRCRCRC) and a further smoothing to the driver tube with another smaller storage cap and resistor. The amp is absolutely dead quiet though AC feeds the heaters and no shielded wire is used. The chassis is earthed and mains fused. Caps are polies and low ESR electrolytics. The power tranni is mounted on split rubber grommets to isolated any vibration from tubes.
Elna caps are used on the output and the two stages are direct linked. Soldering in the audio path is with BWT silver based solder. Resistors are mainly metal film with some 1W carbon and 5W wire wound where required. Pot is an Alps blue velvet with 4oz solid brass gold plated knob. All caps in the PS and in the audio path are snubbed with 0.1uf polies making for a very clean sonic presentation.
As a preamp playing through my KT88 SE UL tube amp "Apparition" exhibited extreme detail with very extended reverb tails. The longest I have heard anywhere. To me this says it is bringing forth every nuance of detail even at the extreme low level of volume. Stereo image is wide with all instruments well placed and standalone. Central image is well defined and feels deep. Bass is good down to 30Hz in my system. On headphones Apparition would keep up or exceed the best I have made to date and no problems driving 250ohm phones. I'm inspired to build a dedicated preamp with this tube of which I have another quad matched set.
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