6CH6 tube. Valve amplifier circuit diagram.

EL821 = 6CH6 = CV4055

Amplifier Circuit Diagrams

The circuit diagrams etc are believed to be good quality and correct. However, please note that several different people have built amplifiers for us in the past (mainly in the 1990s), using valves like S11E12, TT21, E180CC etc.

Since most of those people are now retired, you are free to use this data as a free gift, in good faith for you, an Experienced Electronic Technician to study and aid development of your own ideas

The data you see in this pages is therefore intended to be a Guide Only , not step-by-step instructions.

We try to be helpful, but advice is limited and available by email only. We cannot advise about amplifiers by telephone.

CIRCUIT IDEA FOR STEREO AMPLIFIER USING 6CH6

We have constructed an amplifier (parallel push pull Class AB1) Using 8 x EL821 valves (Plus 6C4, 6BR7, 5U4G).

The following pages show a circuit diagram and data necessary to build this 15 watt stereo amp.

The amp gives excellent crisp clear sound when used with cd player.

EL821 valve is similar physically & electrically to an EL84 but EL821 is more reliable and has a different pin out. (EL821 in class AB1 has Vf 6.3, Vg1 -6.7, Vg2 250V, Ia 30mA, Ig2 4mA)

Free samples of Brimar EL821/CV4055 may be available (limited to 2 per customer) – please enquire.

THE FOLLOWING VALVES ARE NEEDED TO BUILD A STEREO 15W AMPLIFIER

8 pc     EL821            BRIMAR CV4055, UK manufacture original Brimar NOS, very clean, in Government box

4pc      6C4                 MULLARD UK, box anode, glass printed CV4058, in white box

2pc      6BR7               BRIMAR UK, Government box

1pc      5U4G              RUSSIAN, no logo, white box

We have constructed an experimental single channel amplifier using 4 of EL821/6CH6/CV4055 in a parallel push – pull output stage.

We found after much experimenting that class AB1 was the most suitable method of operation keeping the valves well below their maximum anode current levels. Audio quality is excellent and an output of approximately 15 watts was obtained using a 16ohm load.

We also found that changing the output transformer to that of an EL84 and removing 2 of the EL821/6CH6/CV4055 the amplifier still produced excellent audio quality of approximately 8 watts.

The EL821 = 6CH6 = CV4055 is a High frequency low microphony power pentode often referred to as a beam tetrode has now found use as an inexpensive audio output valve. It is qualified to CV specifications and was used in military equipment in vigorous environments.

Although the power output is less than an EL84 the valve is more reliable and consistent in it's characteristics. The closeness of the anode impedance allows many transformers used in EL84 designs to be used for EL821/6CH6/CV4055. The valve sis shorter in appearance than the EL84 and has a different pin out, thus it cannot be used as a direct replacement.

We have constructed an experimental single channel amplifier using 4 of EL821/6CH6/CV4055 in a parallel push – pull output stage.

We found after much experimenting that class AB1 was the most suitable method of operation keeping the valves well below their maximum anode current levels. Audio quality is excellent and an output of approximately 15 watts was obtained using a 16ohm load

We also found that changing the output transformer to that of an EL84 and removing 2 of the EL821/6CH6/CV4055 the amplifier still produced excellent audio quality of approximately 8 watts.

TECHNICAL INFORMATION

Data when used in Class AB1

                        Vg1      =          6.7V

                        Vg2      =          250V

                        Va        =          250V

                        Ia          =          30mA

                        Ig2        =          4mA

Anode Load Impedance =          4500 Ohms (using 4 valves)

                                    =          9000 Ohms (using 2 valves)

The following circuit was designed and built using inexpensive valves as drivers and audio amplifiers. The component values quoted are those found to provide the best audio quality using the transformers and components available to us.

The circuit uses a 6BR7 (similar to EF86) as an audio amplifier, 2 x 6C4 as audio amplifier and phase splitter driving 4 x EL821/6CH6/CV4055 as power amplifiers. Rectification is by a 5U4 or 2 xEZ81, both of which should provide enough current to supply two channels for stereo working.

The gain of the amplifier was sufficient to provide full power output from a standard CD deck.