Katie
KT88 Katie is my first Single-ended stereo amplifier. Pure Kenji design, the two Shuguang KT88s are driven by the pair of 6AN8A triode / pentode wired as "perque drive" and capacitor coupled to the KT88s. The design allows for triode, ultralinear and pentode arrangement: triode is so much nicer to listen to, I've never reverted. Also, there's a switch for up to 6db NFB, that stays "off" (0db). The power supply is a 5AR4 with a 5H choke, 47uf and 200uF Pi filter. Most of the materials were sourced from China: Australia is a DIY'ers desert (or else ridiculously overpriced). Even paying international courier, it's cheaper by far to import myself. The suppliers are in my links page and I can recommend them all. Katie gets used all the time, every day. No noise, very musical and clear, and up to ~6W THD is under 1%. At under 1W (most listening), 2nd harmonic is negligible and inaudible. Katie worked first time, from switch on, a tribute to the excellence of the design. All I did since then was add slightly better coupling capacitors and change to Triode.
Transformer layout
First and most important step in designing your single-ended amp layout, is to decide on the transformer locations and orientation. This is critical if hum is to be minimised. The "nice" looking design is not necessarily correct! Whereas a push-pull amp will cancel induced hum picked up in the OPT, a single ended amp cannot. I was able to get 100uV induced hum from the mains transformer in this orientation...
The wrong way
Same spacing, 90 degree rotation yields an extra 40mV of hum pickup. This would be very audible.
Metalwork
Metalwork comes next. The two OPT on one side of the chassis (like this) optimise the spacing from the mains transformer- much better than a symmetrical layout. Looks are not the main factor but you can still make it look acceptable to others, with care.
Moment of truth
Hooked up to my macbook and the SEAS Thors, I fired Katie up. I did try the power supply first (no valves except the 5AR4) and since it worked ok, plugged in the rest. First time success, thanks to Kenji-san's great design. The amp hardly got switched off for weeks after this.