I wanted an ultra-low output amp for late night noodles. So I've been mucking about with this amp design, which is essentially a valvecaster with an ECC86/6GM8 tacked on the end:
It's powered by a laptop power supply. Output transformer is a 100V line output transformer, less than £5.
Surprisingly, it sounds really ok. Lowest gain setting gives a nice crunchy sound, not skweeky clean but nice for strumming and picking, good note seperation. As you wick the gain up the volume doesn't increase much, but it goes quite AC/DC gnarly. If you stick an overdrive in front, the world's your lobster.
Background hum and hiss levels are really low, pretty non-existant actually.
Volume is surprisingly loud. I'd say it's about the same level as a decent acoustic.
Overall, I'm dead chuffed with it. Only drawback is that ECC86 valves are a little thin on the ground, but I've managed to pick up a few for around a fiver each on eBay. There are some silly prices, though.
Here's my build:
I tried out a few tone controls - SWTC, Moonlight, 18 Watt - but preferred it without, so the tone control in the pic is disconnected. I uprated R8 to 10W wirewound cos it was getting pretty hot. I originally made a filter between the heater supply and the anode supply, but I found that it wasn't necessary - that explains the 3W resistor and the mini-tagboard. Can't be arsed to take them out.
There are probably a load of screw-ups in the design, but it works and sounds good. I'd be interested in any suggestions for improvements.....