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Reference single ended triode (SET) monoblock amplifier
Ruby XR 300B monoblock amplifier
Product Status

The Ruby series of products is the culmination of Roger Hebert's experience and knowledge gathered over 20 years as well as some new insights into circuitry that reduces overall noise levels to unprecedented levels resulting in heightened dynamics to accommodate the ongoing increase in resolution in analog and digital recordings.

Our goal with the Ruby XR monoblocks was to design the best SET amplifier around the most favoured output tube, namely the 300B Western Electric designed, that would be capable of having enough power to drive most speakers from the better high end speaker manufacturers. We also wanted it compatible with all premium 300B tube manufacturers available now and in the future to enable plug in and play with our self biased automatic circuits.

Our exclusive Ruby 300B gain stage circuit design, never before implemented in a tube output stage, has been the most important factor in bringing to fruition the most refined sound ever from a 300B type amplifier. The result is an output stage that has four times the gain of what a single 300B type tube is capable of. This newly developed output circuitry, having no precedent, raises the bar in state of the art development.

Each 300B serial leg forces the two tubes to have the same plate voltage and plate current. This ends up as a forced matched operation with equal grid bias. This forced operation results in even wear of both tubes and likely doubling the lifetime of usage that would occur normally.

The two serial legs are then tied together via the two top plates to drive the output transformer while operating independently from each other. The 4 tubes operate as one giant 300B with 4 times the output power, while at the same time using an output transformer with the same impedance as would be used with one 300B tube

The fact that there are quite a variety of new 300B tubes being manufactured today gives the user a varied choice in selection and voicing of his system. The Ruby XR 300B monoblocks are shipped with the Shuguang Treasure 300B-Z tubes.

Other options for tube swappers to consider include Emission Labs EML 300B XLS and the KR 300B XLS with a filament current of 1.5 and 1.8 amps [ standard 300B is 1.2 Amps ], and the Western Electric 300B.

Circuit Description

Voltage Stage

This stage operates in pure class "A1" single ended plate loaded with independent automatic biasing circuitry for each triode . Both triodes are wired in quasi parallel to take advantage of the 3 dB noise reduction using this configuration.

Driver Stage

This stage also operates in pure class "A1" single ended plate loaded with automatic self-biasing circuitry. This stage operates with high bias current and high voltages needed to drive the four 300B output tubes and do so without driving the 300B grids positive to insure no grid current drive is required. The AC signal is coupled to the 300B grids via 4 independent metalized high voltage, high capacitance Teflon signal capacitors with self healing ability and 1300 Volt DC rating.

300B Output Stage

All 4 output tubes also operate in pure class "A1" single ended self-biased isolated circuitry and transformer coupled output.

The 300B gain stage circuitry is exclusive, ground-breaking and unique, being only one of its kind ever to be implemented in a tube output stage.

Simply stated it is a serial - parallel single ended configuration that results in increasing the 300B stage gain by a factor of four, unprecedented and unique.

Two legs of two series connected 300B's are used in parallel by tying the top plates of each leg to drive the primary of the output transformer. The two bottom tubes of each leg is referenced to ground while the top tubes have floating biasing and signal drive.

If either leg of the series connected 300B tubes go out of range the red LED fault light will come on suggesting that these 2 tubes should be replaced. The left two tubes fault light is designated FL and the right series connected tubes is designated FR.

If the FL or RL red LED's come on then it's time to change that pair of 300B tubes.

Other Features

Dual triple digit LED bias meters read up to 99.9 Volts using a blue readout for constant monitoring.

A LCD hour meter (99,999.9 hours) is now incorporated to keep track of usage, especially important with monitoring the life of output tubes.

The 300B filaments, which also act as the cathode for each triode, require isolated pure 5 volt DC power supplies. Each of the four supplies have a separate 7 volt AC secondary winding connected to a full wave bridge rectifier followed by a 10,000uf filter capacitor and terminated using a solid state 5 volt regulator chip.

The output transformer reacts to this configuration in such a way that it thinks it has only one tube with four times the power rating of one 300B driving it. In other words this stage uses the same ratio of primary to secondary in the output transformer as would be used in an amplifier with only one 300B output tube.

Impedance settings of either 4, 8 or 16 ohms is selectable via two toggle switches located on top rear of each chassis.

Ground loop hum is not a problem - there is no ground lift switch on any Wyetech Labs amplifiers. We employ a special network that does not remove ground safety from the chassis. As a consequence Wyetech monoblock amps don't suffer from ground loop hum pickup!

Power Supplies

Three Toroid power transformers are used in each monoblock with input AC power operation for 115V-120/230-240V 50-60 Hz selected via an internal toggle switch.

Separate DC power supply filtering provide total isolation between the INPUT and OUTPUT stages. This consist of a quadruple-4 (pi) filter for the 500 Volt front end supply and a quintuple-5 (pi) filter for the 1 Kilovolt output stage power supply.

Twin bridge rectifiers rated at 12,000 Volts DC provide the needed voltage and current, that in turn feed the 6D22S (6Kv rating) rectifier tubes that enable the voltage to slowly ramp up due to the 30 second delayed warm up time of the 6D22S.

Custom made polypropylene in oil capacitors with special screw connectors allow easy assembly or removal from Printed Circuit Board

The use of pure LC filter networks with 10 very large polypropylene in oil capacitors, 3 large polypropylene capacitors and six large chokes provide an unparalleled ripple reduction and purity of design unequalled in tube SET amplifiers.

Rectified, filtered and regulated 12 Volt DC provides the power for the input tube filaments of the 1st and 2nd stage. This also contributes to lowering the noise floor.

An Analyst Plus AC Power Oval power cord is supplied with each Ruby monoblock amp.

Mechanical Construction

Extremely rugged all welded steel chassis with 4 mm aluminum top and bottom plates provide a solid firm structure by design. Think of a picture frame doubled up and back to back with the flat top and bottom pieces flush mounted and bolted with 28 stainless steel dress machine screws. This reduces any possibility of vibration induced aberrations affecting the operation of the amplifier tubes.

Top panels are CNC machined to a tolerance of 0.01mm (0.0004 in.).  All components and parts are secured to the top panel via CNC threaded holes

Highly polished 6 inch solid brass handles allow for easy handling and accentuate the chassis styling.

Very high quality powder coated chassis frame with baked on finish to further enhance the beauty of the very symmetrical arrangement of parts.

Satin black finish of the output transformer and dual power transformers mounted on top

Gold plated machined brass footers with 3M rubber feet inserts

Teflon tube sockets with machined brass gold plated tube pins for 5687, 12B4A and 300B tubes for an absolute secure connection and lifetime reliability

Ceramic tube sockets for the high voltage 6D22S rectifier tubes.

Power ON Hour Meter - count to 99,999.9 hours

Dual bias voltage Meters with blue LED readout - 0 - 99.9 Volts DC

Circuit Boards

The components are mounted on three Printed Circuit boards [PCB] which is made from FR4 glass epoxy with double sided copper traces and plated through holes. Both sides have a protective green solder mask. A silk screen is printed in white showing the component layout and parts value. All our PCB's are designed manually with CAD program in house. We use enlarged power and signal line traces to attain the best analog integrity that automatic CAD routing circuit programs cannot attain.

The final assembly of parts to the PCB is done by hand soldering of all components which is superior to automated flow-soldering techniques, by allowing more solder on each and every joint. 4% silver solder is used on all solder joints.

Wiring to the PCB is attached via screw down crimp terminals to allow for ease of repair or removal.

Auto Power Sequencing

A built in time-delay of about 30 seconds in the 6D22S rectifier tubes allows for a slow smooth ramp up in final DC voltages to maximize tube life

In addition a speaker muting circuit is engaged for 35 seconds on power up and 2 seconds before power down for dead silent operation.

Power Switches

Two toggle switches are employed for powering up the unit. The master switch enables the power and the momentary RESET switch engages the power relay to enable the automatic sequencing of operation until the green [ready] LED comes on after the initial time delay. In case of AC electrical power failure during a storm or other event the unit stays powered down until the RESET switch is again enabled. To use the RESET power switch it is important to hold down the spring loaded toggle for 3 seconds when powering up. Once you see the blue LED's light up - you can release the switch

We employ a delayed DC power sequencing that maximizes tube life by preventing cathode emission deterioration.

Power Down Sequence

The master switch is used to power down the unit. On activation of this switch a 2 second time delay occurs that mutes the speaker output before dropping power thus ensuring silence on powering down.

Impedance Matching

Triple impedance outputs for selecting which one of the three [ 4, 8, or 16 ] impedance's you require by the use of 2 toggle switches. Match the numbers to select. When the one switch is set to the 16 ohm position, it overrides the other switch for 4 & 8 ohm selection.


Tube Complement

(per monoblock)

voltage gain (T1)15687WB dual triode JAN NOS Philips USA
driver (T2)112B4A single triode JAN NOS GE USA

Svetlana 6D22S high current high voltage 6KV rectifier

  • 30 second high voltage ramp up until final bias is obtained
  • The 6D22S is preceded by a Solid State Bridge Rectifier rated at 12,000 Volts 1/2 Amp.
output4Emission Labs EMS 300B-XLS tubes with gold plated pins

Frequency Response

20 Hz to 24 KHz (+/- 0.25 dB)

Input Impedance

30K Ohms minimum

Output Impedance

SELECT 4, 8 or 16 Ohms via the two toggle switches by matching the numbers on each switch.

When the one switch is set to 16 ohms, it overrides the other switch setting for 4 or 8 ohms.


22 dB > 1.4 VRMS for full output

Absolute Phase


Power Output

38 Watts RMS - 80 Watt Peak music

Dynamic Headroom

music peaks up to 80 Watts

Universal Voltage Select

115-120/230-240 Volts 50/60 Hz

Power Consumption

385 Watts - each MONOBLOCK


Net: 2 x 68 lbs. ( 31 kg)
Shipping: 2 x 77 lbs.(35 kg)


16.5" W x 24" L x 10" H

41.91 cm W x 60.96 cm L x 25.4 cm H


Note that due to the passing of Roger Hebert, we are no longer able to offer warranty coverage going forward. The sale price has been adjusted accordingly. Sales made previous to January 2022 will have the waranty coverage period honoured.

Warranty coverage for sales prior to January 2022:

  • 5 years on Ruby amplifier front end tubes, namely the 5687 and 12B4A.
  • 18 months or 2500 hours on Ruby XM EMS 300B XLS output tubes, whichever comes first.
Price (USD)
$ 38,000
Price (CAD)
$ 49,500