Often regarded as the first great amplifier, Peter Walker’s original, the Quad II, is a fairly unusual find in the United States. This classic '50s tube amp from across the pond cemented Quad's reputation as a company of influence and integrity. These examples have some character, and one side has a bit of a dent near the terminals, but electronically, they're square in spec and fully tested.
- Condition
- 7/10
- Serial No.
- 58231/61449
- Restoration
- Comprehensive bench test
- Replaced power cords with custom switchable, braided cloth cable
- Upgraded speaker terminals with Cardas solid copper
- Replaced signal caps
- Installed new EF86 tubes
- Cleaned controls, switches, and internal electronics
- Exterior detailed
- Factory Specs
Type Monophonic Valve Power Amplifier
Type Monophonic Valve Power Amplifier
Power output 15 watts into 8Ω (mono)
Frequency response 20Hz to 20kHz
Total harmonic distortion 0.25%
Input sensitivity 1.4V
Signal to noise ratio 80dB
Speaker load impedance 7Ω to 15Ω
Valve complement 2x EF86, 2x KT66, 1x GZ32
Dimensions 13"W x 6.5"H 4.75"D
Weight 18.25 lbs.
- Documentation
Quad II Schematic
- The History of Quad
- The company was founded by Peter J. Walker in 1936 in London, and was initially called S.P. Fidelity Sound Systems. In 1936 the name was changed to the Acoustical Manufacturing Co. Ltd. The company moved from London to Huntingdon in 1941 after being bombed out of London in World War II....
[ Read More ]
- Liner Notes
A Quad II, original or Classic, is a class-A push-pull monophonic amp with only two active stages. The input stage contains two EF86 miniature pentode tubes, each of which is capacitor-coupled to its own output tetrode tube, but only one of which (call it input tube No.1) gets the original input signal. From there, in addition to driving its corresponding output tube, input tube No.1 drives input tube No.2 with a portion of its reverse-phase output, attenuated by some 6dB. Thus the output of the second EF86 is equal to but out of phase with the output of the first, and this balance is maintained through the output transformer's primary, where the full music wave is put back together. This design, called a paraphase circuit, used to be quite popular, arguably because it accomplished phase inversion and voltage gain in one stroke—and so allowed the designer to keep both distortion and parts cost to a minimum.
- Stock No.
- 8075824070877
Often regarded as the first great amplifier, Peter Walker’s original, the Quad II, is a fairly unusual find in the United States. This classic '50s tube amp from across the pond cemented Quad's reputation as a company of influence and integrity. These examples have some character, and one side has a bit of a dent near the terminals, but electronically, they're square in spec and fully tested.
Condition
7/10
Serial No.
58231/61449
Restoration
- Comprehensive bench test
- Replaced power cords with custom switchable, braided cloth cable
- Upgraded speaker terminals with Cardas solid copper
- Replaced signal caps
- Installed new EF86 tubes
- Cleaned controls, switches, and internal electronics
- Exterior detailed
Factory Specs
Type Monophonic Valve Power Amplifier
Type Monophonic Valve Power Amplifier
Power output 15 watts into 8Ω (mono)
Frequency response 20Hz to 20kHz
Total harmonic distortion 0.25%
Input sensitivity 1.4V
Signal to noise ratio 80dB
Speaker load impedance 7Ω to 15Ω
Valve complement 2x EF86, 2x KT66, 1x GZ32
Dimensions 13"W x 6.5"H 4.75"D
Weight 18.25 lbs.
Documentation
Quad II Schematic
The History of Quad
The company was founded by Peter J. Walker in 1936 in London, and was initially called S.P. Fidelity Sound Systems. In 1936 the name was changed to the Acoustical Manufacturing Co. Ltd. The company moved from London to Huntingdon in 1941 after being bombed out of London in World War II....
[ Read More ]
Liner Notes
A Quad II, original or Classic, is a class-A push-pull monophonic amp with only two active stages. The input stage contains two EF86 miniature pentode tubes, each of which is capacitor-coupled to its own output tetrode tube, but only one of which (call it input tube No.1) gets the original input signal. From there, in addition to driving its corresponding output tube, input tube No.1 drives input tube No.2 with a portion of its reverse-phase output, attenuated by some 6dB. Thus the output of the second EF86 is equal to but out of phase with the output of the first, and this balance is maintained through the output transformer's primary, where the full music wave is put back together. This design, called a paraphase circuit, used to be quite popular, arguably because it accomplished phase inversion and voltage gain in one stroke—and so allowed the designer to keep both distortion and parts cost to a minimum.
Stock No.
8075824070877
