The Stereo
70 is a dual 35-watt power amplifier, featuring the high quality and moderate
price which has characterized earlier Dynakit amplifiers. Its electrical
performance is matched only by manufactured amplifiers that cost far more.
The Stereo
70 can be used as apair of 35-watt amplifiers for stereo or as a 70-watt mono
amplifier. Its power and distortion ratings are completely conservative. Its
listening quality is unsurpassed.
Each channel
of the Dynakit Stereo70 employs a 7199 triode-pentode and pair of EL-34 output
tubes. The lower plate voltage used in the Stereo 70 assures long life for
tubes and filter capacitors. In fact this amplifier's components are operated
more conservatively than those in any other commercial amplifier we have used.
The
circuitry of the Stereo 70 is very similar to that of the older Mark II and
Mark III amplifiers, except for the smaller output transformers. Somehow, the
two amplifiers and their power supply have been packaged in a space not much
greater than that of the older mono amplifiers, without crowding and apparently
without running at a higher temperature.
The Stereo
70's frequency response is so flat that it almost seems pointless to plot it.
The power response, in either mono or stereo modes, is nearly as good. The
apparent discrepancy between the maximum power outputs shown in these curves
and those suggested by the distortion curves is simply due to the different
method of measurement. The power response shows the maximum power obtainable
before some distortion of the output waveform can be seen on an osciloscope.
Very small amounts of distortion can be numerical distortion values can be
obtained at much higher power levels.
The Stereo
70 will develop the eqivalent of 18 watts per channel into a 3-mld capacitive
load at 10 kc, which makes it quite suitable for driving electrostatic speakers
at high volume levels. It is absolutely stable and free from ringing under and
conditions of capacitive loading.
Two power
take-off sockets are provided to operate a pair of Dynakit preamplifiers. Each
has its own heater winding to prevent interaction between channels.
Specifications
Power
Output: 35 watts continuous, 80 watts
peak each channel
Frequency
Response: 10 to 40,000 Hz ±0,5 dB
Power
response: 20 to 20,000 Hz (within 1 dB
of 35 watts at less than 1% distortion)
Harmonic
Distortion: immeasurably at power of 10
watts or less
IM
Distortion: less than 1% at 35 watts
(less than 0,05% at 1 watt)
Hum an
Noise: Inaudible, better than 90 dB
(below 10 watts)
Sensitivity: 1,3 volts RMS input for 35 watts out
Damping
Factor: 15
Output
Impedance: 4, 8 and 6 Ω
Minimum
Channel Separation: 55 dB
Power
Consumption: 190 watts 50/60 cps
Preamp
provision: Two power take-offs with
independent heater windings to eliminate interaction. Each 6,3 volts 1 amp, 350
volts Dc 10 ma
Special
Features: two separate power supply sockets for preamplifier; front panel
switch to parallel outputs for operation as a 70 watts monophonic amplifier
Tube
Complement: 4 x EL-34; 2 x 7199; 1 x
GZ-34/5AR4; selenium rectifier
Dimensions
(W x D x H): 13" x 9 ½" x 6 ½"
Weight
: 32 pounds
Finish: chassis and bottom plate bright nickel
plated. Cover finished in charcoal brown vinyl paint.
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