2A3 (300B) SE tubeamplifier

Category: Product Published: Friday, 01 June 2018 Written by Richard Hoogeveen


These are the new HMR-audio Single Ended Class A monoblocks with 2A3-40 from JJ.



This set is completely handcrafted from mostly 10mm thick 6082 aluminum. The front, the back and 6mm upperside are CNC work. Each case weighs 8kg. The total weight is 24kg each complete monoblock.

The 2A3-40 tubes are equal to the 300B from JJ, but has its filament half of that of the 300B. The DC DHT filament regulator for the 2A3 can be "easily" configured for a 300B filament.

The driver tube sitting behind the frontplate is the 6H30P double triode tube, chosen for its linearity, little distorsion and gain and it is actually quite good in driving a 2A3 or 300B. This tube is connected to the HMR-audio/Dalojan MOSFET MU-stage and HMR-audio/Dalojan voltage regulator driven by a Mullard GZ34. The bias current regulation is a conventional one, the autobias is still in development (Arduino based).

The amorph output transformers, chokes and power transformers are famous Tribute ones and are my latest set of Jan. This is a expensive handmade set by Piet Treurniet. Next sets will probably be AE Europe.



You need to drive these amplifier with a volume regulated pre-amp like the HMR-Audio pre-amp or other sources with a volume regulation like a mediaplayer.

In the front you see a part of the HMR-audio tube amplifier controller. It is a Nextion touchpanel and the cpu/software of the controller is capable to controll the amplifier (product page tube/multipurpose controller).

The amplifier tube controller has specific software built for this model.

You can turn it On or Off, measure bias current, temperature, measure high voltages, keeps track of tube hours and you will have audio detection.

You can turn on auto shutdown for 15 min "no audio", too high temperature in Fahrenheit or Celsius, too high bias current.

You can set touchpanel backlight, setpoint bias measurement, level detection of the audiosignal and enable shutdown, level of temperature and enable shutdown, level of bias deviation in +% and enable shutdown.

You can show all measurements of voltages, current, temperature and audio detection on one screen or just a digital  bias meter.

You can turn on a RGB led when you trim your biascurrent (when you are in digital meter bias mode), blueblink, blue, green blink, green, green blink, red, red blink

You can reset your tube hours manually, hours (actually seconds) are stored in EEPROM when you turn Off the amplifier with the touchscreen, other settings are saved in EEPROM on their own pages.

You can set a high voltage delay (optocoupler output available 0-10V which can directly drive a MOSFET), in this amplifier the MOSFET is not implemented, but if you later want to change from a softstarting GZ34 to a diode rectifier you can create your own delayed HV.



Single Ended SE monoblock 8.7Watt class A output

Tubes, 2A3-40 JJ / Sovtek 6H30 / Mullard GZ34

220V / 80Watt, standby 0.9 Watt

Case temperature max about 45 degrees Celsius 

GZ Uk about 390 Volt

Ureg about 360 Volt

Uref about 185 Volts

Ug 2A3 about -70 Volts

4 and 8 Ohm output terminals

THD @ 1 Watt 0.71%

PCB's from HMR-Audio and high quality components

DHT regulator from Rod Coleman (really good and no plans to design my own)

75mA biascurrent


These high end amplifiers are for sale, you can contact me with the contact form. 









The price of 1 (in many hours) handcrafted amplifier is 6499,- euro (price can change because of customer wishes and market prices).

Fully populated amplifier pcb's can be made available.


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