After
years of research, development and day-to-day manufacture with the
EL519 series of pentode tubes, Tim de Paravicini has come up with a new
and exciting Triode configuration. Conventional triode connected
pentodes have the second grid tied to the anode, which results in a
halfway compromise between a pentode and a triode. This neither has the
efficiency of the pentode, nor the linearity of the triode. Tim de
Paravicini's Enhanced Triode Mode (ETM) goes one step further, and
creates a true, highly linear triode from a robust pentode tube.
Instead of driving the normal Grid One with signal, this is tied down to
the cathode, and thus becomes an invisible, transparent element, and
part of the cathode. Signal is fed into the tube's Grid Two, and in this
configuration, Grid Three has no effect - it can either be connected to
earth, or left floating. The ETM behaves like a true triode and is in
fact more linear than the majority of directly heated triodes. Compared
with the latter, it has the additional advantage of being a tough, more
robust tube, capable of much longer operational life.
Push-pull power amplifier
operating in pure Class A, enhanced triode mode. Zero overall
negative feedback. 32 wpc stereo (bridgeable to 64 watts mono) into
4, 8, or 16 ohms. Uses EL519 output tubes. Self-biasing. Balanced
and unbalanced operation
The first amplifier to use the ETM configuration was the '859, and with
some justification the '861 could be regarded as a push-pull version of
the '859. However, this is more than a slight understatement: each
output transformer has a massive 5 kilogram weight, with no feedback
applied around it. The circuit is balanced push-pull from input to
output, allowing balanced (professional-style) inputs as well as
conventional unbalanced (RCA phono jack socket). Similar to the '859,
the circuit is direct-coupled. Tube choice is not critical; perfect
operation does not rely on matched tubes, nor on user adjustable bias.
Output power is 32 watts per channel, 20 Hz - 20,000 Hz. The half power
bandwidth is in excess of 16 Hz - 60,000 Hz, both with low total
distortion, and no overall feedback. Tube complement: 2 x ECC83, 6 x
PCC88 and 4 x EL519. Amplifier weight: 27 kilograms.
Subjectively the amplifier has the same 'family' sound as the EAR 859.
Listeners will find it builds heavily upon this, with an increase in
authority and attack. The lower bass has real grip and feel with this
amplifier, way in excess of the 32 watt power rating while the treble is
smoother, cleaner and sweeter, mainly due to the lack of overall
feedback. A single word can sum up the 861: ''effortless.'' It has real
power and control, the power to convey the emotion of the most demanding
of recordings, whether the source be our preferred analogue or digital.
