Dynaco Mark VI Vintage Monoblock Tube Amplifier Pair, 120W

$2,399

This listing is for a working set of Mark VI Monoblocks in working condition.

Features rare XLR inputs for an amplifier this age. Cool bias meter on the front with rack handles.

This pair of amplifiers is labeled "Dynaco Wired", however they have underwent a significant modification at some point in the past.

The majority of the electrolytic capacitors were replaced, film bypass capacitors were added to the various power supply rails, and slow start relay circuits were added to delay the B+ voltages.

Other modifications may have been performed that we are unaware of that sharp Dynaco aficionados may recognize. 

Both amplifiers were tested to their rated power of 120W. Both meter lamps and meters are working properly.

Tubes include RCA 7199, and a mix Sylvania and Philips USA 8417.

Please see our pictures for overall condition.

Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - BALANCED XLR Connectors - Better

Kimber Kable - BALANCED XLR Connectors - Best

Kimber Kable - Speaker Cables - Better

Kimber Summit Series Monocle XL Speaker Cables (PAIR) - Best

Kimber Summit Series BiFocal XL Bi-Wire Speaker Cables (PAIR) - Best If Applicable 

More from Dynaco:

The Mark VI is a vacuum tube high power basic power amplifier designed for the professional sound installer.

Vacuum tubes are most often favored 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.

Dynaco Mark VI Professional Power Amplifier - Instructions For Assembly Operation

The SkyFi Testing Process for Tube Amplifiers:
We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect resistors and other passive components for signs of overheating. If tube arcing has occurred in the past we can usually spot discoloration on the output tube sockets. On vintage units we often spot check select capacitors for value and ESR.

If the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use an Amplitrex AT-1000 Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy. We document the results of each tube and replace any weak or suspect tubes before proceeding. When we power on tube amplifiers for the first time we usually use a variac and current limited AC supply and slowly raise the voltage up to nominal mains level while monitoring plate, screen, filament, and negative bias supply voltages where applicable. If everything is in order we feed a low level test signal into the amplifier’s input and monitor its output on an oscilloscope across an 8 ohm dummy load. At this point we are just looking to verify basic function and confirm that the output transformers are not damaged. Once we have verified that the amplifier is safe to operate, we connected it to full mains power. For fixed bias amps we set the bias to manufacturer spec. For cathode biased amps we monitor the plate to cathode voltage to determine if the output tubes are operating in a safe range. Once the output section is verified we move onto bench evaluation.

We start by feeding the input of the amplifier with a low level 1KHz test signal, slowly increase its amplitude while monitoring the amplifier’s output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. For tube amps we like to run this test at least twice. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when it has fully come up to temperature. We find this step to be essential, especially for vintage units.

Specifications:
Power output:
120 watts into 8 Ω (mono)

Frequency response:
10 Hz to 40 kHz

Total harmonic distortion:
1%

Damping factor:
14

Input sensitivity:
1.6 V

Signal to noise ratio:
95 dB

Speaker load impedance:
4 Ω to 16 Ω

Valve complement:
4 x 8417, 1 x 7199

Dimensions - Each:
19 x 10.5 x 8.75 inches

Weight - Each:
55lbs 

Item

Included

Original Box

Not Included

Manual

Yes Included

Remote

Not Applicable

Cables

Yes - Power Only

Physical Condition

6 / 10

Working Condition

10 / 10

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