"Toccata" - KT88 SE UL amplifier

This simple two stage power amp was built from 95% parts on hand. I had all the expensive parts, tubes, OPTs, power tranni, base etc. Inter-stage caps also on hand and are Russian PIO greens. I have used these in so many builds and always sound excellent. Only a handful of cheap components required purchase. Most of the parts on-hand I've had for nearly twenty years. Time to put them to good use and I haven't made a tube power for a while. Included in the parts I have had for a while were a pair of mustard caps (0.1uf) which I used as bypass caps (across Ck) on the 6N1P driver tube.

The power tube in the image is a JJ Blue Glass KT88 of which I have had - and never really used - for a long while. I bought them as a quad matched set for a PP amp I had years ago. The power tube can be swapped out for 6L6, EL34 and others with no bias tweak. The 6N1P is Silvania. Power tranni and choke are Hammond and OPTs Edcor. Ceramic sockets. Base is Australia Spotted Gum rubbed with a finishing oil and top plate paint Epoxy Enamel. Top plate is 2mm Al and the tranni is isolation mounted to reduce HF vibration to the tubes.

As is my usual practice there is no PCB or shielded wire. Cat5 solid core used throughout. Most P2P wiring uses a large tag brd. with components aboard then wired P2P from the brd. This results in a lot of hookup wire. A better solution is small 5 tag tag brds at each tube, two brds. each then mount components to them. Far less hookup wire, parts are right at the tube.

I'd built a SS rec. brd. with two SF 3A diodes and 150uf of 400V filtering a long way back. Using it here with a 5H choke and another 470uf in double Pi configuration (CLCRC) resulted in a dead quiet robust PS. Noise at the speaker post is 0V with the meter on the 200mV scale. That's quiet!

The amp only produces 3.5W RMS into eight ohms but sounds louder on my 90db+ sensitive speakers. Bass tests down to 20hZ and upper frequency is 70KhZ. Bass in my room is heavier and deeper than my DIY SS amps and there is a real sparkle at the top end. Best I've heard so far. Very transparent amp to listen to. Gain is 15db low for a power amp but only requires 300mV for full output.