Dynaco Dynakit mkVI
Power Amplifier Kit
The Mark VI is a vacuum tube high power basic power amplifier designed for the professional sound installer.
Vacuum tubes are most often favoured in their ability to withstand enormous physical and electrical abuse - conditions frequently encountered in discotheques, public address and musical instrument applications.
Its rugged construction and utilization of superior components, including the patented Dynaco Super Fidelity transformers, permit continuous duty at full power, while maintaining safe operating margins.
Protective isolation of the load from the driving circuits, and uniform power output into a variety of load impedances are inherent in all designs which use an impedance matching transformer.
The Mark VI employs a basic circuit arrangement which all Dynaco vacuum tube amplifiers have used since the inception of the Mark II amplifier in 1955.
Refinements of the operating parameters have been incorporated for circuit balance, stability, and for drive capability.
The components used have been selected to protect against failure, and all parts are operated conservatively to assure superior performance and proper operation for many years.
Power output: 120W into 8Ω (mono)
Frequency response: 10Hz to 40kHz
Total harmonic distortion: 1%
Damping factor: 14
Input sensitivity: 1.6V
Signal to noise ratio: 95dB
Speaker load impedance: 4Ω to 16Ω
Valve complement: 4 x 8417, 1 x 7199
Dimensions: 19 x 10.5 x 8.75 inches
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Reviewed May 07th, 2014 by guest
A rare & less-than-stellar valve amplifier, fraught with issues that should help deter a collector's ardor...
Basically a MkIV with an extra set of higher power output valves (8417 vs. EL34/6CA7), and compromised by excessive cheapness of build. Looks good in pictures, less so in the (cheap!) metal. Doesn't sound especially powerful for its rating, it was noticeably outpointed in a comparison I did with a Marantz 8B (35W vs. 120W) driving Martin-Logan CLS electrostatic speakers. The Marantz played them louder!
And even into easy (less reactive) loads, the Mk.VI displays a persistent subjective lack of bass below 35-40c/s, with a bump in the 80-120c/s region that really doesn't substitute very well...
Mids & highs are about as nice as the Mk.IV/Stereo 70's, but the 7199's triode section kangaroo splitter is overmatched trying to drive the 50k grid resistance & Miller effect of the 8417's, which can only tolerate 1/3rd the grid resistance of an EL34 when both are used with fixed bias; as is the case here.
Metalwork is junky, my amps have rusted noticeably with bubbling under the faceplate(!!!) black paint, also the el-cheapo rack handles (nothing more than bent-up rectangular strips of low-grade steel!), and nasty black screws (more low grade steel). Leaning on one of the transformers whilst fiddling about caused the flimsy chassis to buckle & permanently crease slightly!!!
Some examples have potted transformers (my current set does), all the others I've seen don't. The potted transformers sound just as blunted & flabby & lacking in the bottom octave as all the other unpotted examples I've heard (about 3 sets).
The meter looks good, but isn't terribly accurate. There is only ONE bias adjustment for all four output valves, more cost-cutting stupidity! The 8417 has the highest transconductance (24ma/V) of all the audio power valves ever made, twice as much as the next highest (EL34 & EL156/KT120). Valves therefore match poorly & bias is typically wildly all over the place! No big deal if you buy 100 8417's and match them into a couple of quads; but the valve is long-discontinued, costs a mint, will NEVER be put back into production (too difficult to manufacture because of the incredibly precise grid alignments necessary in such a high-slope valve!), and you'll never find a vendor (or twenty, all combined!) with 100 of them anyways, even if you did have $10-20k to spend on sifting through the goofy NOS that's left...
Oh, and only Sylvania made them originally, they were the very last audio power valves (along with Mullard's beautiful little ECL86/6GW8) ever designed in the Golden Era.
Dynaco screwed up large designed around a dead valve, they obviously had no concern about future maintenance. This has resulted in all sorts of conversion modifications, either to 6550/KT88's (a bad choice, as grid resistance issues are the same as the 8417) or to EL34/6CA7. The latter conversion allows you to raise the combined grid resistance from 50k to 150k, which SHOULD be helpful. In practice though, the bass remains just as shabby as it did with the 8417; suggesting that the OPT is the culprit as beefing up power supply capacitance dramatically didn't help much either!
Due to demand, GE started making 8417's in the early 80's after Sylvania finally stopped. Good samples sound better than Sylvania's, but typically short GE cathode life & sloppy QC meant that most samples have mu-slop (cutoff issues related to biasing & matching) problems. I'd say 30% of GE 8417's were defective right out of the box, and that's a conservative estimate. Even then, good GE 8417's typically need about 5 more volts (negative) on the grid to bias the same as a Sylvania, making mix-matching a VERY bad idea!
Gob only knows what Internet Valve rippers have sitting in their caddies awaiting your eager purchase!
Apparently only 1000 of these silly boat-anchors were made, or perhaps it was 1000 pair. Reliable information seems scant. What is considered true is that it was put into production around 1976, long after the rest of the valve line, at the behest of the Japanese Dynaco importer whose customers were apparently clamouring for something along these lines. Considering all the nasty mid-fi tranny-trash they sent us, it seems they mostly got what they deserved!