Dynaco Dynakit mkIV
Power Amplifier Kit
The Mark IV Amplifier uses a circuit arrangement based on that of the Dynakits Mark II and Mark III which have become world famous for superior quality while essentially simple and trouble free.
The new 7199 tube is used as a pentode high gain voltage amplifier directly coupled to a cathodyne phase inverter. All parameters are adjusted for minimum distortion.
This type of phase inverter has the unique advantage that its operation is independent of tube ageing so that no adjustments are required in maintaining optimum performance.
An internal capacitive feedback loop balances the phase inverter at the highest frequencies, and the arrangement provides accurately balanced driving signals to the output tubes, which are EL-34's operated well below their maximum ratings.
The output tubes use a fixed bias arrangement which is set through use of Dyna Biaset (patent pending) which provides optimum linearity of the tubes and minimizes the effects of unbalanced components.
The connection of the output tubes includes a small percentage of screen loading which improves the regulation of the output stage and makes it comparatively uncritical of load impedance.
Power output: 40W into 8Ω (mono)
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 1%
Damping factor: 15
Input sensitivity: 1.3V
Signal to noise ratio: 90dB
Speaker load impedance: 4Ω to 16Ω
Valve complement: 2 x EL-34, 1 x 7199, 1 x GZ-34, 1 x selenium rectifier
Dimensions: 5 x 14 x 6.5 inches
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Reviewed May 07th, 2014 by guest
One of the very finest Dynaco valve amplifiers, so one of the finest valve amplifiers...ever!
Simply 1/2 a Stereo 70, with a slight upgrade in power output due to a more enthusiastic power transformer which output about 30VAC more...and burns out alot! Fortunately, there are reproductions available to deal with the problem...
IMHO, sound quality is down slightly from a Stereo 70. I find the extra 50VDC on the anodes of the EL34/6CA7 adds a slight hardness to the sound, the ST70 is a tad more relaxed & refined by direct comparison. Otherwise, the circuit is IDENTICAL. Output transformers are identical, and like the ST70, the power transformer is underrated for the job. Despite the virtually side-by-side placement of the input jacks on the Stereo 70, I don't find the Mk.IV has much of any advantage in terms of subjective channel separation; i.e., imaging.
Not an amp to lust over if you already have a Stereo 70; definitely something worth shopping for if you don't!