The 845 Pure Triode Tube. 1931 Vintage. A powerful alternative to the 300B.
The “Reviewers Amplifier”
With several pairs sold to leading reviewers, we are told that one of their outstanding qualities is the ability to give consistent results with virtually any type of speaker. Something many “high end” amplifiers cannot do. Like all our amplifiers the design is simple letting the magic of the valves shine through
The RCA 845, probably the ultimate power triode valve dates from about 1931 when the only way to get higher powers was to make valves bigger and run at higher voltages. The later EL34 and KT88 types are far more efficient but many think do not sound as pleasing.
When we first released the MB845 in the UK they were greeted with great acclaim by the hi fi press and customers, for power and value, but above all their unique sound quality. It has become THE reference valve amplifier for Hi Fi World magazine.
Many other 845 amplifiers use 4 stages, often using 300B valves as driver valves, but this more complicated design does not allow the 845 to reach its full potential in terms of transparency and maximum output of 110w, useful if your speakers need a lot of power. But the power is secondary to the large bandwidth and low distortion available.
For some people only a large triode valve like the 845 can give the golden warm tone which is so pleasing, with its feeling of air and space and sense of realism.
The MB845 MK I has truly become a legend in the UK, but hi fi fans were soon asking if there was more we could do to improve the performance. With the MB845 MK II, we have used all our expertise to create our ultimate triode PP amplifier. The MB845 MK II has an improved power supply, an upgraded driver stage, more linear driver chokes, and our new series of bigger LDT series of low distortion transformers. These have caused the MB845s to put on 11kg each to 37Kg each, so be careful lifting!
A feature of the MB845s is the high and low sensitivity. This enables MB845s to work with both “Passive” and conventional pre amplifiers. This is not done by attenuation which reduces quality, but genuinely changes the gain of the input.
The sound is best described at “an iron fist in a velvet glove”. These amplifiers will suit almost any speaker and situation. They have no particular down side other than size and weight.
Icon Audio MB 845 MK II M
Specifications and Features
- Improved LDT Tertiary winding output transformer
- Improved dual 6SN7 high current driver circuit
- Choke regulated power supply
- All hand wired point to point
- No printed circuit board to ‘colour’ sound
- Class A, all Triode front end
- 2x 845B precisely matched for best performance
- 1x 6SL7 first stage gain valves
- 2x 6SN7 driver valves, choke loaded plates
- 845 AC heating for max life and max reliability
- 30.5V (typical) output at clipping point 8 Ohms*
- Giving approx 20 Watts of Pure Class A
- Can be used with passive or active pre-amp
- 450mv (high) & 1000mv (low) input sensitivity.
- Signal to noise level -90db* (approx)
- Hum and noise 0.5mv (low sensitivity)*
- 6SL7/6SN7 DC heater circuit for minimum hum
- Freq response -1db points= 6Hz 27khz
- Freq response -3db points= 6Hz-57kHz
- Source impedance 0.7Ω (8Ω taps, low sensitivity)
- Damping factor 13
- Gain 67 (high) 30 (Low)
- THD typically less than 0.1% @ 1w. 0.14% @ 8w (1kHz)
- 4 & 8 ohm loudspeaker taps
- Custom tertiary hand-wound mains/output transformers
- Attractive Plexiglass cover included in the price
- Audiophile quality 2W precision resistors throughout
- Solen audio capacitors (or optional Jensen Copper foil)
- Silver PTFE audio cable
- Gold plated Input & speaker terminals
- 220/240volts (115 v adjustable)
- Comprehensive manual supplied
- Full instructions for DIY valve change included
- Power consumption: 180w min, (290w max sine wave) each
- Size in cm W24, D57, H28 mm ( inc cover), 37kg each (Allow space for connections and ventilation)
- Carton 2x 66x35x38cm + 1x 57x31x32 Total 84kg
(Specifications subject to change, errors & omissions excepted November 2016)
*The 845 is designed specifically for audio use. It not a transmitter valve, unlike the 811 and 805, its grid cannot be driven positive making it easier to drive and more linear.