Transcendent Sound       Vacuum Tube OTL Audio Amp Kits

The Bruiser

UltraLinear Mode: 60W/Ch into 4 ohms and 50W into 2 Ohms

35 Watts/Ch of Triode Power into 4 and 2 Ohms

Kit without transformers and Tubes Only $499

NOTE:  Due to the high cost and weight of transformers, we are offering this kit without them.  Output transformers can be Edcor CXPP50-3.4K - 50W, 3.4K (4 ohm) and the power transformer from Antek AS-2T350 - 200VA 350V.  

There are many 4 ohm loudspeakers that require a lot of reactive current.  Many times, their impedance dips down into the 2 ohm range, especially in the upper bass power band.  Tube amps typically have a difficult time providing this high current drive.  Not this one.

The Bruiser is a heavy duty stereo tube amp designed to handle these types of speakers.  It has been designed around the magnificent KT120, one of the toughest tubes available.  The amp can also handle the even more powerful KT150.  Other tubes from the 6550/KT88 family will work, but the best overall sound can only be obtained from the KT120.

As expected from any Transcendent Sound product, this amp is dead quiet, fast and clean.  No muddiness or coloration of any kind.  The Bruiser can be connected in UltraLinear Mode for more power, but triode operation provides  the cleanest, most musical performance by far.  

The circuitry is straightforward, without any solid state modules or control circuits.  No bias adjustments are ever required.  Matched tubes will give the best performance but unmatched tubes will work perfectly well.

This is a low feedback design with only 5 dB of global feedback.  The low impedance of the big tube plates keep distortion low.  The driver tube is the ECC99 which provides the most lush and musical sound.  The input tube is the 12AU7.  Many variations of the 12AU7 are available allowing for tube rolling to adjust the sound to taste.  

This is a USA made, economical tube amp that can drive some of the most difficult speaker loads on the market.  Thirty-five watts is quite a lot of power when it is this clean with high curent available.

Here are some performance measurements in triode mode:

This is the noise spectra with no input and into to 4 ohms.  The net RMS noise figure is only 110 microvolts dBA spread out over the audio passband.  Notice that the highest noise component is only 35 microvolts at 500 Hz.  All of the rest are even lower.  This corresponds to a signal to noise figure referenced to full output of 100 dBA.

The above shows harmonic distortion of a 500 Hz signal at 1W into 4 ohms.  Net distortion is less then 0.5%.  The graph shows a tiny second order harmonic at 1000 Hz and one small third order component at 1500 Hz and that's abut it.  The one watt performance is critical because most listing occurs at less than one watt.  

This is a chart of harmonic distortion at 25W.  The net amount is just under 1%.  Notice that the single largest component is a third harmonic at 1500 Hz.  All of the other components are very low.  That means the amp is holding together and staying very linear at high power.

This is a picture of a 10 KHz square wave at 1W into 4 ohms.  There is an almost complete lack of ringing and overshoot.  That is quite good for a transformer coupled tube amp and reveals excellent phase linearity.

This picture shows the 10 kHz square wave into 4 ohms at high power, 25 watts.  The waveform is holding together quite well with minimal ringing.  Phase linearity is then quite good at high power levels indicating clean sound.

Specifications in triode mode:

Power:  35W per channel into 4 or 2 ohms.

THD: less than 1% up to full power.

Power bandwith: +/-  1 dB from 30 Hz to 30 kHz .

Noise: 110 microvolts A weighted, or 100 dBA referenced to full power.

Output impedance: 2.5 ohms

Gain: 28 dB or 400 mV for full power.  Can be driven by passive preamps.

Input impedance:  100 kOhms.

Dimensions:  17 inches wide, 11 inches deep, and 8 1/2 inches high with Kt120 tubes.

Weight: 26 lbs.

Power consumption:  165 watts at idle.

Voltage: 115-120V or 230-240V, 50-60 Hz.

Tube compliment: four- KT120, two- ECC99, two- 12AU7

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