Pyramid of Sound Equipment begins with Amplifers.

Remember the Food Pyramid?   Basics at the bottom building up to the top.

Well, basic amplification begins with....

First Choice....  Mono Amplifiers.  Typically two to four are used in a system.   One or two for each channel.

One Mono Amplifier for each channel can neatly handle the full range of audio.

Or Two Mono Amplifiers for each channel when bi-amping.   For example a four amp array for two channel sound would often consist of a Solid State mono amp for each channels low frequency reproduction, and a Tube amp for each channels mid to high frequency reproduction.   Pairing Solid State with Tube amplification can provide more affordable and amazing sound quality.

Enjoyable Low Frequency sound requires more amperage than enjoyable Mid range and High range audio reproduction requires. Since Solid State equipment can produce high amperage at a much lower price than Tube equipment Solid State equipment becomes a logical and satisfying choice for lower frequency reproduction. And because Tube equipment excels at producing high quality mid-range and upper range audio, Tube equipment is often a first choice approach to high quality mid and high range sound reproduction.  Lower amperage Tube amplifiers are fairly affordable making bi-amplification with Solid State and Tube equipment together a logical choice.

Second Choice....   Stereo Amplifiers.   One "Basic" Amplifier to power the full range of both channels.

Quatre 2 channel amplifier

Or again a variation of Bi-amplification would be with two "Basic" Stereo (two channel) Amplifiers to power ranges between the lower and upper frequencies, one two channel amplifier to power the lower frequencies and another two channel amplifier to power the middle and upper frequencies.  This can be a mix of Solid State and Tube two channel amplifiers or all Solid State or all Tube equipment.  If your listening level tends to be less deafening than mine, and your speakers are fairly efficient (will discuss speaker efficiency later) you might be able to get an affordable level of amplification for the lower frequencies using Tube equipment solely for the full range.   However I feel the merits of Tube equipment are primarily in the mid and upper ranges of the sound spectrum and it seems illogical to spend extra money to amplify lower frequencies with Tube equipment.  I am not so sure there would be appreciable improvement in lower frequency sound reproduction when choosing Tube equipment over Solid State.

An all Solid State Bi-amplification can be highly rewarding and cost effective.
For example an BK ST-140 two channel amp would be ideal for cost effective amplification of the middle and upper ranges, and the same is often said for the Adcom GFA-535 two channel amp.  I own both and can confirm from experience that both of these Solid State two channel amplifers are exceptional in producing middle and upper range tones with finesse.  They do quite well with lower frequencies too but might have difficulty on their own producing the low frequency sound volume some desire.   Pairing either of these with a more powerful two channel amplifier (or pair of mono-blocks) for the lower frequencies is a nice way to get an amazing quality of sound for the commoner.   Champagne sound for a beer budget.

Next posting is Pre-Amplification.