The Mullard 3-3 Single Ended Tube Amp Kit

In the mid 1950s Mullard engineers published some audio amplifier designs to highlight the performance capabilities of their tubes. One of the most innovative and effective circuits was the Mullard 3-3, a 3 Watt Single Ended Monoblock Amps. It used an EF-86 or 6267 voltage stage directly coupled to an EL-84 or 6BQ5 power tube. This amplifier design has an excellent sonic reputation among audiophiles. This is surprising since the amplifier was never commercially produced, Mullard only released a manual for DIY construction. Once you hear the sound performance, you realize why it has the reputation it does.

Due to the resurgence in single ended tube or valve amplifiers and kits, we are pleased to offer the audio enthusiast the opportunity of own or build this excellent design. The chassis, circuit and layout are almost identical to the original. The transformers, designed by Peter Chappell of F&S Transformers, offer significantly better performance than the originals. Since the output transformer has three times more steel laminations than the original, the transformers are rotated 90 degrees from the original orientation.

The Mullard 3-3 is available in the following configurations and pricing(price does not include shipping):

Mullard 3-3 Stage I: Transformer Set of two power and two output transformers $ 390.00 USD

Mullard 3-3 Stage II: Kit consisting of transformers and painted punched chassis $ 445.00 USD(All parts minus signal capacitors, resistors, tubes, and hook-up wire)

Mullard 3-3 Stage III: Completely assembled and tested monoblock pair $ 845.00USD

Circuit Description "Excerpts from Mullard Manual":

"This circuit has been devel-oped to meet the demand for a simple amplifier of reasonably high quality. The amplifier uses three Mullard valves: an EF86, an EL84 and an EZ80. The output terminations of the circuit are suitable for almost all kinds of loudspeaker, but, although the circuit is designed to make the most effective use of the single output valve, the best possible results will only be achieved if a suitably housed high-quality speaker is used."

"The EF86 in the voltage-amplifying stage is used under conditions approaching those of starvation operation. With a high value of anode load resis-tance (R5 is 1Megohm) and reduced values of anode and screen-grid voltage, the gain of the stage is raised two or three times above that obtained under normal operating conditions. This increase is attributable mainly to the fact that, because the voltage at the anode of the EF86 is very low, direct coupling can be used between this anode and the control grid of the EL84 in the output stage. Thus the shunt loading on the anode circuit of the EF86 is least at low and medium frequencies."

"The use of direct coupling between the stages necessitates a higher cathode voltage in the output stage than is required with RC coupling. The value of the EL-84’s cathode resistor is thus greater than is usual in the standard cathode or self bias design. The screen-grid voltage for the EF86 is taken from the cathode of the EL84. In this way, negative D.C. feedback (which is essential in a directly-coupled circuit to stabilise the operating conditions of both stages) is applied to the voltage amplifier."

The Output transformer has a primary load impedance of 5000 ohms. It also provides secondary tappings with a nominal impedance of 4, 8 and 16 ohms.

The power supply uses the EZ80 tube rectifier. A resistor is used between the cathode of the EZ80 and the reservoir capacitor C9 for voltage control. The anode of the EL84 is supplied from C9, and the screen-grid is supplied through another filter network R12, C6.

General Description:

The chassis are aluminum. The chassis and transformer bell ends are finished in medium gold metallic paint (see picture).

The transformers used on these kits are designed and wound by Peter Chappell. He's the transformer designer used for all the Abacus Audio and Chimera Lab's products. Power transformers are available for line mains voltages of 100, 115, 220, 240 VAC at 50 & 60 cycles.

The output transformers are not only larger than those originally specified. They offer a wider bandwidth and offer a sonic improvement verified in listening evaluations. The power transformer is an isolation type with a grounded shield. The windings are concentric wound for low stray fields and low noise.

Mullard 3-3 Specifications

Operation: Single-ended Pentode Class A operation
Tube complement: EZ80, EF86, EL-84
Power Output: 5 Watts
Sensitivity: 100mv for 3 Watts
THD: 0.6% at 1 Watt, 1.0% at 3 Watts
Output Impedance: 1.5 ohm for 15 ohm load
Output secondary tappings: Nominal 4,8 and 16 ohms
Damping Factor: 10
Frequency Response: 20Hz to 30kHz at 3 Watts +/-1dB
Dimensions per monoblock amp: 8.0" wide, 6.0" deep and 6.0" high
Weight: 18 lbs net, 21 lbs packaged (for a pair of amplifiers)

If you have any additional questions, contact me and I will get it to you when I have it available.

Alliance Audio Products – Tube Amplifiers and Tube Kits Audio Tube Amplifiers Audio Tube Kits Audio Transformers ChimeraOne Home Page Classic Audio VIntage Tube Audio DIY Tube Audio ChimeraOne@worldnet.att.net