|Stereo 60 Power Amplifier|
The Stereo 60 power amplifier is my own dream-amplifier. The EL34 ultra-linear output stage can actually deliver about 35 Watts at clipping, with distortion reaching 0.1% at about 25 Watts.
The amplifier is closely related to the Stereo 50 model, which at first glance looks quite similar. The external differences are:
The Stereo 60 has an input attenuator switch (some later Stereo 50 units also have these)
The first stage valve socket is mounted above the chassis instead of from below
A power supply filter choke was included in the Stereo 60 in the middle of the chassis. In the photo above the round can in the middle is where the filter choke is located. It has been reported (but not confirmed) that some Stereo 60 units had a large choke (like that shown), but most were much smaller that this.
Circuit-wise, the Stereo 60 is almost identical to the Stereo 50, except that the power supply voltage is higher - the power transformer outputs more voltage, and the filter choke results in less voltage drop in the filtering circuit. More impotantly though, the Stereo 60 uses type 8615 output transformers (with 25% screen taps) where as the Stereo 50 uses type 3925 output transformers (with 50% screen taps, making operation of the output tstage closer to triode, with less power). As a result the Stereo 60 delivers slightly more power than the Stereo 50.