The Icon Audio MB 845

The 845 Pure Triode Tube. 1931 Vintage. A powerful alternative to the 300B.

Beautiful Versatile Affordable

Designed in Leicester by David Shaw, founder of Icon Audio. 845s the ultimate power triode! The 845 valve dates from a time (when the only way to get high power was to make valves bigger and more powerful as opposed to more efficient like the later EL84/34 KT88s. Just as the Western Electric 300B set new standards for high power and low distortion, the RCA 845 dating from about 1931 became THE definitive high power valve for audio and even radio transmitters.

WHY IS IT SO GOOD? Like the 300B, the 845 characteristics are very linear (input V. output).
WHERE DO THEY FIT IN? Nothing beats the sound of triode output valves, so probably someone who needs more power than 300Bs can offer.
WHY AREN’T THEY MORE POPULAR? The 845 is not an easy valve to work with. Many 845 amplifiers are complex using 300Bs as driver valves which are more expensive than the 845s. This leads to huge very expensive amplifiers which can sound “soggy” and “slow”. In keeping with our preference for simple designs, with a faster more transparent sound but with plenty of power, we used all our expertise to create a practical design similar to our popular MB90 KT90 mono-blocks.

DID YOU KNOW:

Two 845s in class AB1 produce as much “Class A” as a pair of KT66/300Bs in pure class A, but more than four times the power in AB1. And their low idle current causes much less stress on the tube. As it is less than 50% of the maximum rating! Preserving tube life.

Surprisingly from such big amplifiers is how well they perform at low powers. Their agility and detailed texture of strings and vocals is quite astounding. A feature of the MB845s is the high and low sensitivity. This enables MB90s to work with both “Passive” and conventional pre amplifiers. This is not done by the usual attenuation which increases noise and reduces quality, but genuinely changes the sensitivity (or gain) of the input.

Another new feature of the MB90s is the power saving “Warm up/Standby” switch. This prevents valve cathode stripping during start-up and enables the amplifier to remain in standby on low power without wasting valuable valve life or electricity (only 38w). The amplifiers will then start instantly, fully warmed up. The brand new design features polished stainless steel chassis, 20 mm solid alloy front panel. And our famous stainless steel and Plexiglas valve cover to create a stunning visual impression.

On the scales at 50Kg (pair) this amplifier is no lightweight in quality or performance and should give many years of excellent service. As each amplifier is prepared to your order here in Leicester. We can offer a range of upgrades including our unique HT delay, premium and “new old stock” valves, the superb Jensen Copper foil “oil in paper” capacitors. Ask us for a quote. As a small company we make customer service a priority. Valve amplifiers do need a little more TLC than transistors, they will need a valve change every few years (circa £190 per pair) but the sonic benefits are more than worth it. When re-valved, you get a new pair of amplifiers again!

An Icon engineer is always on hand at the end of the phone... Total Peace of mind service!

This is an early prototype of the MB 825 mono-bloc amplifier (current spec does differ see pdf)

Features and Specification

• Comprehensive manual supplied
• Full instructions for DIY valve change included
• Full instructions for 845 valve testing included
• Meter supplied for valve 845 bias/condition testing
• All hand wired point to point
• No printed circuit board to ‘colour’ sound
• Class A, all Triode front end
• Fitted with the newly designed 845”B”
• 2x 845 precisely matched for best performance
• 2x 6SL7 first stage gain valves
• 2x 6SN7 driver valves, choke loaded plates
• HT delay unnecessary as 845s have instant start
• AC 845 heating for max life and max reliability
• 90w (approx) RMS output at clipping point*
• Giving approx 15 Watts of Pure Class A
• Can be used with passive or active pre-amp
• 440mv (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 28 62
• THD typically less than 0.1% @ 1w. 0.14% @ 8w (1kHz)
• 4 & 8 ohm loudspeaker taps
• Custom hand-wound mains/output transformers using
Japanese special long grain iron and low oxygen copper
oven baked in resin to minimise mechanical hum and
increase reliability.
• Attractive valve cover included in the price
• High quality 2W metal film, & wire-wound resistors
• Blue LED mains indicator
• Polypropylene audio capacitors (or optional upgrades)
• Silver TEFLON audio cable
• Ceramic valve holders for minimum leakage
• Gold plated Input & speaker terminals
• 230/240volts (120v on request)
• Power consumption: 180w quiescent, (290w max sine
wave) each
• C E, ROHS, WEEE compliant where applicable
• Size in mm W, D500, H ( inc cover), 23kg each (Allow
space for connections and ventilation)
• Shipping H 45, W 62.5, D 37cm 26kg
*May be subject to around 5% variation due to valve tolerance)

Specifications subject to change, errors & omissions excepted. Gen 16/03/09)

Downloads

For full details of this product (including pricing, options and delivery details) pls download the PDF.

PDF