PhonoGraph

Manufacturer of tube amplifiers

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Integrated Tube Amplifier PhonoGraph 60

Circuit

Williamson Push-Pull Ultralinear class AB1

Nominal power output:

2 x 25W ( f = 1kHz sinus THD=0.21% )

Maximal power output

2 x 35W ( f = 1kHz sinus THD=1% ) 2 x 60Wrms

Frequency Response

10Hz÷65kHz ( Power output = 5W sinus ±3 dB / 0dB for f = 1kHz )
15Hz÷60kHz ( Power output = 25W sinus ±3 dB / 0dB for f = 1kHz )

Frequency Response Irregularities

±0.1 dB (f=20Hz÷20kHz Power output = 5W)

THD dla f = 1 kHz

0.08% ( Power output = 5W sinus for f = 1kHz )
0.21% ( Power output = 25W sinus for f = 1kHz )

THD for f = 20Hz÷20kHz

<0.2% ( Power output = 5W sinus band f = 20Hz ÷ 20kHz )
<0.5% ( Power output = 25W sinus band f = 20Hz ÷ 20kHz )

SNR measured on the output

<0.01mV ( 104dB below signal level at 8Ω )

Input impedance

100kΩ ( f = 20Hz ÷ 20kHz )

Line inputs

4 x

Input sensitivity

550mVrms ( Power output=25W )

Nominal impedance

4Ω , 8Ω or 16Ω

Tubes/valves

2 x GZ34S , 4 x 6L6GC , 2 x ECC99 , 2 x ECC82 , 2 x EM84

Power supply

300VA

Weight

30kg

Dimensions ( without tubes )

430x375x120 mm

Description of the construction


The PhonoGraph 60 amplifier has been designed using Williamson’s Ultra-linear circuit scheme.

A Williamson circuit refers to amplifier which design uses the same principles as the design published by D.T.N. Williamson on the pages of Wireless World Magazine in 1947. Its power level has unique characteristics and had significant impact on HiFi technology. This is one of the first described constructions striving to reach the best parameters of sound reproduction. It is considered as the first HiFi amplifier.

Technical advantages of Williamson’s circuit:

• Very low output non-linear and intermodular distortion with high energy efficiency.
• Low internal resistance, high resistance against impedance changes. It is very important with modern speakers, where complex audio drivers are used and their impedance changes significally along with frequency.
• Oversized transformers, which on the one hand make the device heavier, but on the other allow excellent low tones transmission.

PhonoGraph 60 amplifier contains four main function blocks. The initial stage and inverter (phase splitter) are build on ECC 82 valve. Initial stage is directly cojugated with inverter, working in shared load arrangement and featuring very big symmetry. Signal from phase splitter is not directly transmitted on to output stage, but on to intermediary stage, implemented as symmetric differential amplifier built on ECC 99 valve . Such solution allows to deliver high amplitude and low distortion signal to the output stage.

The output stage is based on legendary beam tetrode vacuum tubes 6L6 GC and works in AB1 class (the first screen grids work only in negative voltage ranges). Up to 10W output power, the tubes work in pure A class. The output stage is conjugated with output transformer in ultra linear circuit arrangement.

Ultra-linear circuit technique has been patented by Alan Blumlein in 1936 and first used by D. Hafler and H.I. Keroes in 1951. Its characteristic feature is the local feedback through a combination of mesh screening to primary tap on the output transformer. Unhitch is arranged so that it goes back to 20 - 50% of the anode voltage of the variable. In this way, the flash mode is intermediate between the triode (100% of the signal on the mesh shield), and pentode (0% of the signal on the mesh shield). This arrangement provides a very low harmonic distortion and intermodulation and low internal resistance only slightly worse than the triode with incomparably higher energy efficiency.

Above-mentioned arrangement provides very low non-linear and intermodular distortion and also low internal resistance – only slightly worse than triode’s – with incomparable energy efficiency.

Output transformers are multilayer-produced on El trunking. Their core cross-section has been carefully suited to ensure excellent transmission of both - low and high frequencies.

The output stage tubes work at Auto Bias mode, which provides stability of the amplifier through the usage period. It completely eliminates necessity for the user to perform any adjustments or checks through the whole „life” of tubes.

Our amplifiers are equipped with contemporary produced tubes by companies like JJ-Electronic, except the EM84 (NOS) tube, which is a VU meter.

Assembling technology is based on combined method of spatial installation and printed circuit technique. It assures full parameter repeatability of all our products.

Audio electrical system has been built on dual-monoblock tube technology. It eliminates noise and reverb pervading between the channels. Semiconductor components have been used only in transformer’s soft start circuit and to delay output stage tubes’ power supply. As an engaging elements we used polypropylene capacitors MKP.

To achieve proper impulse response, we installed Low ESR, high capacity (2000mF) battery in the power supply unit. It results in excellent dynamics and bass drive.

The amplifier’s housing is made from laser-cut stainless steel. Natural steel and powder coated matt black color versions available.

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