Brand new homemade 275 Watts 8 KT88 based Push-Pull tube amplifier
2100 euros

I live in France (near Compiegne city, 75Km North-East from Paris) 

This amp was build in purpose to be reliable and intended for heavy use during whole nights in parties.

(not built in purpose to make watts for cheap). No tubes which flash nor tubes which lose specs quickly nor amp which goes into self oscillation and destroy itself or speakers. 

Homemade Output transformer (300Watts down to 20Hz, 450Watts down to 30Hz) with amorphous core (it's for high grade O.T.) and homemade High Voltage power transformer.

Choke input, Tubes rectifiers, voltage regulation. (not cheap design) 

Intelligent automatic start, the H.T. is applied only when the KT88 are ready and only if the bias is present (bias protection).

Intended for 4ohms use (for example, 2 paralleled 8ohms subs, or 4 paralleled 16ohms subs, or 8 serie + paralleled combinaison of 8ohms subs)  

or 2.66ohms use (for example, 3 paralleled 8ohms subs, or 6 paralleled 16ohms subs, or 12 serie + paralleled combinaison of 8ohms subs)  

Avoid 8ohms if you want it reliable (this O.T. is designed without multi outputs, in purpose to use it at full capacity (for all multitaps O.T., when 4, 8, 16ohms taps, when using the 4ohms tap, you in fact use only half of the copper of the secondary)(and usually, making multitap make you slightly losing coper wires space making your O.T. less efficient))

When changing KT88 tubes (which shouldn't be required before at very least the next 1000 hours of use as tubes are new (except the time spent for the many tests), and that the amp is designed for the tubes to last long), the amp is very easy to set, as there is a two ways ampermeter which tell you in live if the tubes are not balanced when no signal (if it's the case, change the tubes positions until it's balanced), and it also show if it's not balanced when driving them hard (in this case, there is a multiturns potentiometer inside the amp that you can set, which change the drivers output ratio)

S/N > 66dB, this amp is very quiet, less than 15mV RMS background noise when gain potentiometer fully ON, so, you got around 0.00005 Watts of noise in the speaker while up to 275 Watts of sound.

(no "hummm" or "bzzz" in the speakers, except if you have ground loop problem or noisy preamplifiers of course).

Damping factor: enough for any kind of speaker.

Here the measured specs of the amps:

275 watts Push-Pull tube amplifier

Frequency range f-3dB: 20Hz-20 000Hz (but Output Transformer optimized for bass not high-frequencies)

Distortion (THD) at 1 watt with a 4 ohms load:

- 20Hz 0.17%

- 40Hz 0.052%

- 80Hz 0.030%

- 100Hz 0.031%

- 200Hz 0.028%

- 800Hz 0.036%

- 1000Hz 0.049%

- 8000Hz 0.16%

Distortion at 10 watt with a 4 ohms load:

- 20Hz 0.088%

- 40Hz 0.041%

- 80Hz 0.043%

- 100Hz 0.043%

- 200Hz 0.057%

- 800Hz 0.17%

- 1000Hz 0.21%

- 8000Hz 0.98%

Distortion at 50 watt with a 4 ohms load:

- 20Hz 0.28%

- 40Hz 0.17%

- 80Hz 0.12%

- 100Hz 0.11%

- 200Hz 0.16%

- 800Hz 0.41%

- 1000Hz 0.50%

- 8000Hz 3.08%

Distortion at 240 watts with a 4 ohms load: 

- 20Hz 1.17%

- 40Hz 0.51%

- 80Hz 0.54%

- 100Hz 0.47%

- 200Hz 0.50%

- 800Hz 2.47%

- 1000Hz 3.66%

Distortion at 306 watts with a 4 ohms load:

- 20Hz 14.7%

- 40Hz 13.7%

- 80Hz 13.7%

Distortion (THD) at 1 watt with a 2.66 ohms load:

- 20Hz 0.17%

- 40Hz 0.045%

- 80Hz 0.029%

- 100Hz 0.034%

- 200Hz 0.047%

- 800Hz 0.090%

- 1000Hz 0.11%

- 8000Hz 0.39%

Distortion at 10 watt with a 2.66 ohms load:

- 20Hz 0.13%

- 40Hz 0.11%

- 80Hz 0.10%

- 100Hz 0.12%

- 200Hz 0.13%

- 800Hz 0.39%

- 1000Hz 0.46%

- 8000Hz 1.99%

Distortion at 50 watt with a 2.66 ohms load:

- 20Hz 0.90%

- 40Hz 0.58%

- 80Hz 0.54%

- 100Hz 0.54%

- 200Hz 0.55%

- 800Hz 0.82%

- 1000Hz 0.97%

- 8000Hz 4.23%

Distortion at 275 watts with a 2.66 ohms load: 

- 20Hz 1.66%

- 40Hz 1.15%

- 80Hz 1.08%

- 100Hz 1.13%

- 200Hz 0.98%

- 800Hz 3.35%

- 1000Hz 4.15%

Distortion at 360 watts with a 2.66 ohms load:

- 20Hz 14.6%

- 40Hz 13.3%

- 80Hz 13.4%