New types of tubes for push-pull and stereo amplifiers

New types of tubes for push-pull and stereo amplifiers.
Radioamator i Krótkofalowiec, Rok XI, Marzec 1961, Nr 3

Among the many new types of receiver tubes that have recently been introduced to the market by Western European manufacturers, the ELL80 and PLL80 dual speaker pentodes deserve special attention. The idea of placing two tube systems in one bulb has been known since the birth of the now obsolete ECL11 tube, which at the time was a kind of revelation; it was followed by further, more modern types, such as ECL82 ... 86 and their equivalents in the U and P series. Placing two end pentodes in one balloon is, however, something completely new, resulting from the current needs of the electronics industry, in particular from the needs of modern stereo technology.

The final stages of the stereo amplifiers were initially filled with the standard ECC83 + 2xEL84 set, consisting of a total of three tubes. The use of ECL82 tubes made it possible to reduce the number of  tubes to two, and - with the same number of stages - had an impact on the cost of the device. However, equipping the same circuit with the ECC83 - ELL80 set is more rational at the same cost, as it allows for a favorable and transparent assembly, allowing you to easily avoid undesirable microphonics, various types of couplings, etc. As you know, two stages with a very strong overall amplification (in the case of an ECL tube) is quite critical and requires careful elaboration of both electrical and mechanical systems in terms of the stability of the system. The popular ECL11 tube was particularly capricious in this respect.

Fig. 1. Schematic diagram of the 2 x 3W amplifier with ECC83 and ELL80 tubes and its technical parameters.


Fig. 2. Schematic diagram of the 2 x 2.6W amplifier with ECC83 and PLL80 tubes and its technical parameters.
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Fig. 3. Schematic diagram of the push-pull amplifier with ECC83 and ELL80 tubes and its technical parameters.


Fig. 4. Schematic diagram of the push-pull amplifier with ECC83 and PLL80 tubes and its technical parameters.

The basic technical data of the new tubes is provided in the table below:

ELL80 tube
Uż = 6,3V, Iż = 0,55A

  Class A
(one system)
Class AB
(two systems)
Ua 250V 250V
Ue 250V 250V
Ia 24mA 2x21...26mA
Ie 4,4mA 2x2,3...8,8mA
P0 3,0W 8,5W
k 10,5% 5,0%

 PLL80 tube
Uż = 12V, Iż = 0,3A
 

  Class A
(one system)
Class AB
(two systems)
Ua 200V 200V
Ue 200V 200V
Ia 30mA 2x24...25mA
Ie 4,4mA 2x4,5...6,5mA
P0 2,6W 5,0W
k 10,0% 5,0%

Here are some typical application examples of new tubes.

Two-channel low frequency amplifier with ECC83 and ELL80 tubes.

Fig. 1a shows a schematic diagram, and Fig. 1b - technical parameters of the system. It should be emphasized the high sensitivity of the amplifier, which achieves the full output power of 2x3W with the control of the initial stages with a voltage of only 65mV.

Two-channel low frequency amplifier with ECC83 and PLL80 tubes.

The power of the amplifier shown in Fig. 2 is 2x2.6W with 10% distortion; this power drops to the value of 2x1.8W with lowering the supply voltage to 170V.

Push-pull amplifier with ECC83 and ELL80 tubes.

The circuit shown in Fig. 3 is used in higher class radio receivers. The amplifier delivers 8.5W of acoustic power (AB class) with relatively low distortion.

Push-pull amplifier with ECC83 and PLL80 tubes.

This version of the amplifier is used in the audio part of television sets. The circuit shown in Fig. 4 provides 5W of acoustic power with 5% distortion. When the supply voltage is lowered to 170V, the output power drops to 3.5W.

K.W.