Kaiju 300B Amplifier Kit


2 in stock


Kaiju is our premium 300B stereo amplifier that can also be wired as a monoblock for double the power output.
Do you have super efficient speakers? You can learn more about the DC Filament Supply upgrade for this kit at this link.

This product has a universal power transformer and can be used worldwide by following the wiring instructions in the manual. Please note that international customers will need to provide their own power cord.

Save 10% when you buy 2 or more (when not on sale). It typically takes anywhere from a day to a couple of weeks to get your kit ready to ship.


Kaiju. It’s Japanese for “strange beast”.


The Kaiju 300B amp is indeed a beast, capable of 8 watts per channel in stereo configuration and 16 watts of 300B magic as a monoblock. You will need to order two kits for a 16 watt stereo monoblocks pair setup. Kaiju has even better performance than our legacy Paramount amp, a universal power transformer, your choice of AC or DC filaments, and the biggest and best transformers we have ever made.


Kaiju is our finest high quality single ended, parallel feed, directly heated triode amplifier kit, that can be configured as a stereo 8 watt per channel parafeed SE 300B amps or strapped as a 16 watt monoblock.


The maximum power output of up to 9 watts per channel in stereo 300B configuration allows the Paramount to work very well with high end loudspeakers of sensitivities as low as 93dB. One can use two Kaijus strapped to monoblocks for a 16 watt per channel system that will drive even inefficent 89 dB/1W/1M speakers to 100dB+ levels. Conversion from one circuit to the other is possible with some easy rewiring that is clearly explained in the assembly manual. Wired either way you get the articulate bass, sweet midrange and extended treble that parallel feed, active loaded and shunt regulated Bottlehead products are known for.


An option to upgrade the filament supply from super quiet AC to astonishingly quiet DC makes the Kaiju a great choice for super efficient, noise sensitive horn speakers too. And one can use a stereo Kaiju on each channel for biamping speakers designed for the purpose.


We consider this a Skill Level 3 kit. It has some PC boards and lot of parts. It will probably take three or four evening to complete the kit. It would make a great second kit for more experienced builders, though quite a few first timers have completed them as well.



The Circuit


The input stage uses a 5670/2C51 tube. The 5670 is a very sweet sounding, particularly linear tube (important when using an output tube as linear s the 300B!) There’s enough variety of brands to make tube rolling interesting and it is not prohibitively expensive. One half is configured as an actively loaded voltage amplifier using our Camille Cascode Constant Current Source for super quiet, dynamic, linear performance. The other half of the 5670 operates as an actively loaded hybrid shunt regulator for the voltage amplifier, giving the driver stage great extension of both bass and treble information.


The driver PC board has a soft start function. This delays the B+ to the plate of the driver tube for about 30 seconds at startup. I should note here that once fired up, the amp will need to sit for about 20 minutes after you turn it off for the circuit to “reset” itself and function with the soft start. This soft start may be useful in extending the lifetime of the tubes.


A custom Bottlehead plate choke loads the output tube and the output is via a high quality parallel feed coupling capacitor and custom Bottlehead parallel feed output transformer with 2,4,8 and 16 ohm taps to work with a broad range of speakers. The two amplification stages are R-C coupled.


The amp can be configured as a two channel stereo amp or strapped into a monoblock circuit with twice the output power.



The Power Supply


A custom Bottlehead power transformer supplies AC or optional regulated DC to the 300B filaments and high voltage is supplied to the driver stage shunt regulator and the output stage plate choke via smooth sounding Schottky rectifiers and a conservatively designed CRC filter for quiet operation.



The chassis


The laser cut and random brushed aluminum chassis is 10″ x 16″ and a hefty .120″ thick. The chassis plate sits in an attractive Pacific Northwest alder wood base that you assemble and finish to taste. All of the inductors are mounted with low noise in mind resulting in a classic look that highlights the beauty of your glowing tubes. Input, output and power entry jacks are at the rear of the chassis plate. A easily accessible power switch sits at the center front of the chassis, and equally easy to access hum balance pots reside next to the output tubes.



Component quality


Laser cut chassis plates and alder wood base kits are made for us here in the Pacific Northwest. The custom Bottlehead inductors – the finest we have made to date, composed of a universal power transformer and output iron with an audible improvement over the Paramount in bass control and punch – come from Northern California. Rectifiers are Cree high voltage Schottkys for B+ and high current Schottkys for the optional regulated DC filament supply. Capacitors are quality brands like of Panasonic, Dayton and Solen polypropylene, and Nichicon electrolytic. Resistors are carefully selected for each application and include 1% metal films for precise voltage and current tolerances, and overrated wirewound resistors for output tube cathode loads. Hookup wire includes both Alpha teflon insulated 22 ga. solid core copper wire for high voltage connections, Belden solid core shielded twisted pair for super quiet heater wiring, and Mogami input signal cabling. Tube sockets are ceramic and input RCA jacks are by Neutrik.





• Power: stereo 300B ~ 8+ Watts, strapped as monoblock ~ 16+ Watts


• Bandwidth: 16Hz to 34kHz at -3dB


• Sensitivity: Full power at 1.56v


• Gain: About 8 at the 8 ohm output tap (21.5 dBV)


“The Kaiju is officially a good move for me. I love my Stereomour but the Kaiju is digging a little deeper I think, even hi passed around 70hz, the lower midrange/upper bass seem to be more dynamic and the mids are amazing, I’m really loving it. It seems to be a bit more effortless with my 94dB speakers although the difference is subtle at the levels I listen.”


“…I have a sound that I am ecstatic about. Finally have bass, midrange, and crystal clear treble, imaging, depth, pinpoint instrument placement and musicality. I can’t drag myself away and keep going through my music collection hearing details and experiencing things I have not before.”


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Additional information

Weight 37 lbs
Dimensions 18 × 12 × 12 in
Upgrade Options

Basic Kaiju, Add the DC Filament Supply

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