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is an increasing dependence on having only one of the output tubes controlling the
linearity.
When there is higher bias current there is a larger region of dual linearity, and there is
less generation of higher-order harmonic distortion products, particularly at higher power
levels. For the most critical listening at higher power levels, the FULL mode provides the
purest sound reproduction and the CONSERVE mode is the logical choice for less
critical listening, or listening at lower levels. However, you should evaluate the sonic
merits of listening critically at the various settings. You may overestimate the amount of
power you need and the CONSERVE or PARTIAL modes may not compromise the sonic
purity in your situation. Also, the output impedance is different for the different modes
and this generally does affect the sound.
The 211/845 follows other Berning designs in that the tubes are operated at relatively low
temperatures for long life. The exception is the operation of the output tubes if the FULL
CLASS A mode is used. However, these tubes are designed to provide long service life
when operated hot. The idle plate-dissipation for each output tube is 71 watts in the
FULL mode; 37 watts in the PARTIAL mode; and 17 watts in the CONSERVE mode.
Added to this is a 30-watt heater, and hence these tubes run quite hot. Routine tube
replacement on the 211/845 should not be needed with normal usage. 10,000 to 20,000
hour lifetime should be expected. Additionally, it is recommended that the amplifier be
powered down when it will not be used for several hours or more, otherwise it can be left
powered. If the FULL CLASS A or PARTIAL mode is used in listening, switching to
CONSERVE mode can be done to place the amplifier into a quasi-stand-by mode if there
is a break in listening for a period of time.
The output impedance of your 211/845 amplifier can vary from 1.7 ohms (moderately
high damping) to 5 ohms (moderately low damping), depending on the tube choice and
CLASS setting, as detailed in the Specifications section. This provides a rather wide
range of speaker damping characteristics.
While many amplifiers have a large amount of negative feedback to achieve high
damping, this is not always optimum. The impedance of most speakers varies with
frequency. Often this shows up most dramatically with a rise in impedance near the bass
resonance frequency. When an amplifier has relatively high output impedance, coupling
more power into the speaker at those frequencies where the impedance is higher changes
the system frequency balance. Speaker designers generally try to design for a flat
frequency response using an anechoic chamber. Home listening environments generally
fall far short of the ideal acoustic properties of the anechoic chamber, and the tube choice
and/or CLASS switch gives you, the amplifier user, a means to modify the normal
speaker response to compensate for room acoustics and personal preference.
Technically, speaker damping relates to the control that the amplifier has over the
position of the speaker diaphragm. High damping applies tighter voltage control over the
speaker and causes the amplifier to absorb and stop speaker cone motion due to the
(speaker cone) overshooting its desired position in response to transients. However, many
