The choice of an amplifier is governed by considerations of cost, power and flexibility. As the amplifier is the heart of a hi-fi system it is well worth buying the best one can afford.

The main amplifier and the control unit or pre-amplifler may be bought as separate units or combined on one chassis; the term 'amplifier' used alone usually refers to the combination.
The control unit should have independent bass and treble controls, a selector for various types of records and inputs for radio and tape.

The provision of a filter is well worth while. In the main amplifier, wide frequency range alone is not enough; low distortion at full output is essential and the frequency range and distortion figures must be known for full output, not for some nominal figure. Except for the very smallest rooms, a 10 watt amplifier would be the minimum and 15 or 25 watts may not be excessive in a large room with relatively inefficient loudspeakers.

If the system is to be used for stereo listening then either two complete amplifiers or a double amplifier and stereo control will be necessary. If a system is to be used for single-channel reproduction at present but possibly to be converted to stereo later, choose units which may be converted without making any of the components redundant. Imhofs staff will always be happy to advise you of the most suitable unit for your requirements.

Stereo unit: usable for single-channel if required. Valves: two EF86 (Z729 or 6267), two ECC83 (12AX7). Distortion: less than 0.1%. - Hum and noise: better than -70db. Input sensitivity (for 1.4V rms output): radio and tape 70 mV rms, mic. 1.5mV rms. Frequency response: ± 1.5db, 20 to 20,000 c/s. - Dimensions: 10"w x 6"d x 3'h. - Weight: 9lb. - There is also the single-channel Quad II control unit.

Valves: two EF86 (Z729 or 6267); two KT66 (5883 or 6L6G matched); one GZ32 (54KU or 5V4G). Power output: 15 watts throughout the range 20-20.000 c/s. Distortion: at 12 watts output not to exceed 0.25% at 25 c/s. Background: 80db referred to 15 watts. Input sensitivity: 1.4V. rms for 15 watts output. Frequency response: within 0.2 db 20-20.000 c/s; within 0.5db 10-50.000 c/s. Output impedances: 15 ohms and 7 ohms. Power supply: 200-250 AC single phase (or 100-130 AC). Consumption: 90 watts (excl. control unit, tuners, etc.). Dimensions: 13w x 4"d x 6"h. Weight 18lb.

Valves: two EF86, six ECC 83, four EL84. Power output: 10 watts rms. per channel (20 watts peak). Total harmonic distortion: 0.1% at 10 watts output at 1,000 c/s. Hum and noise: 80db below full output. Frequency: ± 1db 20 to 20,000 c/s. Damping factor: 30. Dimensions: 4" x 14" x 13" deep overall.

Valves: three ECC83, four EL84. Power output: 10 watts rms per channel (20 watts peak). Distortion: 0.1% for 10 watts at 1 K/cs. Hum and noise: 80db below full output.
Frequency response: 20-20,000 c/s ±1db. Damping factor: 30. Output impedances: 32,16, 8 or 4 ohms.
Power supply: 200-250V AC or 100-125V AC. Dimensions: 14" x 8" x 4".

Power output: 15 watts (peak). - Distortion: less than 0.1% at full output. Power response: 3db from 25-65,000 c/s.
Loudspeaker impedance: 15 ohms. Power supply: AC 200-250V, or 115V, 40-100 c/s. Dimensions: 11" wide x 6" deep x 4" high

Power output: 10 ± 10 watts (15 4- 15 watts peak). Distortion: less than 0.1% at full output. Frequency response: ± 0.5db 20-20,000 c/s. Loudspeaker impedances: two 15 Ohms; adaptor for twin 4 ohm speakers available. Power supply: 210, 230, 250V. AC or 105, 115, 130V AC. Dimensions: 15"w x 8"d x 4"h.

Valves: two EF86 or Z729 or 6267. Total harmonic distortion: less than 0.1% for 1.25V output. Hum and noise: approximately 66db below full power output on radio and tape positions and approximately 60db below on other inputs. Dimensions: front panel 1H" x 4-jV'; chassis 10"w x 3d x 5h. Weight: 4 lb.

Valves: two EF86 or Z729 or 6267. Total harmonic distortion: less than 0.1% for 1.25V output. Hum and noise: approximately 66db below full power output on radio and tape positions and approximately 60db below on other inputs. Dimensions: front panel 1H"x 4tV', chassis 10"w x 3d" x 5"h. Weight: 5 lb.

Valves: one EF86 or Z729 or 6267, one ECC81 or B309 or 12AT7, two EL84 or N709 or 6BQ5, one GZ34 or 5V4 or 5AR4. Power output: 14 watts rms. maximum. Total harmonic distortion: 0.1% at 12 watts output (±1db) at 1,000 c/s. Hum and noise: 85db ± 3db, below 12 watts with a source impedance of 25,000 ohms. Sensitivity: an input of 125mV at 1,000 c/s gives 12 watts output.
Frequency response: ± 0.5db, 20-20,000 c/s. Damping factor: 25, measured at 1,000 c/s. Loudspeaker impedances: loudspeakers of any impedance between 3 ohms and 20 ohms may be used. Power supply: 200-250V 50-100 c/s or (alternative model), 100-125V 50-100 c/s. Consumption: 75 watts. Dimensions: 10" x 7" x 5". Weight: 14lb.

Valves: one EF86 or Z729 or 6267, one ECC81 or B309 or 12AT7, two EL34 or KT66 or 5881, one GZ34 or 5V4 or 5AR4. Power output: 32 watts rms. maximum. Total harmonic distortion: 0.1 % for 25 watts output (± 1db) at 1,000 c/s. Hum and noise: 86db, ± 3db, below 25 watts with a source impedance of 25,000 ohms. Sensitivity: an input of 125mV at 1,000 c/s gives 25 watts output. Frequency response: ± 0.5db, 20-20,000 c/s. Damping factor: 25, measured at 1,000 c/s. Loudspeaker impedances: loudspeakers of any impedance between 3 ohms and 20 ohms may be used. Power supply: 200-250V, 50-100 c/s or, (alternative model) 100-125V, 50-100 c/s. Consumption: 130 watts (135 watts with Leak pre-amplifier). Dimensions: 10" x 7" x 6". Weight: 17 lb.

Valves: one EF86 or Z729 or 6267, one ECC81 or B309 or 12AT7, two KT88 or 6550, one GZ34 or 5AR4. Power output: 50 watts rms. maximum. Total harmonic distortion: 0.1% for 50 watts output (± 1db) at 1,000 c/s. Hum and noise: 83db ± 3db below 50 watts with a source impedance of 25,000 ohms. Sensitivity: an input of 125mV at 1,000 c/s gives 50 watts output. Frequency response: ± 0.5db 20 c/s to 20,000 c/s. Damping factor: 15, measured at 1,000 c/s. Loudspeaker impedances: loudspeakers of any impedance between 3 ohms and 20 ohms may be used. Power supply: 200-250V, 50-100 c/s or 100-125V, 50-100 c/s. Consumption: 145 watts. Dimensions: 11" x 9" x 6". Weight : 28 lb.

Balance control: dual ganged, permitting perfect channel balance and giving facilities of: (1) varying channel gains from zero to maximum to compensate for differences in loudspeaker sensitivities, and (2) monaural listening on either loudspeaker system.

Each channel is identical in gain within 0.5db and the characteristics of each channel are as follows: Power output: 12 watts rms. maximum. Total harmonic distortion: 0.1% for 10 watts output (± 1db) at 1,000 c/s. Hum and noise: 80db ± 3db below 10 watts. Sensitivity: an input of 125mV gives 10 watts output. Frequency response: ± 0.5db, 20-20,000 c/s. Damping factor: 25.
Loudspeaker impedances: between 3 ohms and 20 ohms. Power supply: 200-250V, 50-110 c/s, or 100-125V, 50-100 c/s. Consumption: 130 watts. 18

Valves: three ECC83 (B339 or 12AX7), four EL34 (KT66 or 5881), one GZ34 (5AR4). Power output: 60 watts rms max. (30 watts each channel). Total harmonic distortion: 0.1% for 30 watts rms output per channel at 1,000 c/s. Hum and noise: 80db below max. output with source impedance of 25,000 ohms. Sensitivity: 120mV input gives max. output. Frequency response: ± 0.5db, 20 to 20,000 c/s. Damping factor: 25, measured at 1,000 c/s. Loudspeaker impedances: any between 3 and 20 ohms.
Power supply: 200-250V, 50-100 c/s or (alternative model) 100-125V, 50-100 c/s. Dimensions: 10"w x 13"d x 6"h. Weight: 27 lb.

Valve: ECC83 twin-triode. Frequency response: (controls level) ±1db. 40-15,000 c/s. Dimensions: 8"w x 5"d x 2"h. Weight: 3lb.

Valves: four EL84, two ECC83, two GZ34. Power output: 12 watts per channel (15 watts peak). Total harmonic distortion: 0.2% at 12 watts output, 1,000 c/s. Hum and noise: -85db below 12 watts. Sensitivity: 750mV rms. for 12 watts. Frequency response: ± 0.25db, 20-20,000 c/s. Damping factor: 20. Loudspeaker impedance: 4, 8 or 16 ohms. Power supply: 200-230-250V 50 c/s or 110-115-125V 50-60 c/s. Consumption: 125 watts. Dimensions: 14" x 8" x 5". Weight: 33 lb.

Valves: two EF86, two ECC83, four ECL86, GZ34. Power output: 12 watts rms per channel (14 watts peak). Total harmonic distortion: 0.25% for 12 watts. Hum and noise: 80db below 12 watts. Frequency response: ± 1db, 30-20,000 c/s. Power supply: 110-250V AC. Consumption: 95 watts. Dimensions: (in teak case) 15" x 10" x 7". Weight: 21lb. Also available in chassis form. Dimensions: 14" x 10" x 5". Weight :23 lb.