Two-channel gramophone amplifier

J.F., "Two-channel gramophone amplifier"
Radioamator 1961/02

We present an interesting schematic diagram of a phono amplifier operating slightly different from the generally accepted principles. It is a two-channel amplifier with one input and two separate outputs, one of which is intended for low-range playback and the other for high-frequency reproduction.

Such an amplifier system allows separate regulation within wide limits of low and high tones. Both channels work in the output stage in a normal Class A system, which greatly simplifies the construction of the amplifier. The first stage of amplification works on the EF40 pentode in a conventional system. In the control grid circuit of this tube there is a "volume control".

The second stage operates on the ECC40 double triode in the cathodie phase inverter system. In the circuit of one of the anodes of this tube there is a RC filter that allows adjustable lowering of the pitch. The output stage of this channel for "low" tones working with the EL84 pentode has a potentiometer for "volume control" in the control grid circuit. The second ECC40 tube anode controls the "high" tone amplifier stage, working with the EL41 tube. The tweeter channel has no separate regulation.

Due to the fact that both channels work in a normal Class A system, the difficulties associated with the rather troublesome winding of a loudspeaker transformer in push-pull systems is eliminated. The acoustic effects obtained (as Yug2GR Yugoslavian YU2GR provides) are not inferior to those obtained from more sophisticated Class B amplifiers. However, we should remember about the right choice of speakers (loudspeaker Gł1 - for low tones, and Gł2 - for high tones).

Instead of low frequency choke in the filter of the power supply, part of the primary winding of the output transformer was used for this purpose.

In the absence of such a transformer, you can use a conventional choke.

According to the Yugoslavian monthly "Radioamater" 10/59.
Compiled by J.F.