Sound Valves M60C Tube Monoblock Amplifier Pair

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Sound Valves is the name taken after Dynaco stopped selling DIY kits in the 1990's and set up shop in Columbus Ohio.

The M60 amplifier could be considered the next version of the Dynaco MKIII.

The parts used on these amps, aside from chassis and main board, follow the Dynaco design principal of being readily available. Meaning most parts are available from either Mouser or most modern tube suppliers today.

There is great support out there for anything Dynaco and that includes these amps. Any place that repairs or mods Dynaco equipment can work on these amps.

The M60 audio circuit topology is a four stage, single channel power amplifier.

The front end consists of an all triode, Class A gain stage, phase splitter, and low impedance drivers.

The output stage uses 6550 tubes and operates in triode or ultra-linear mode selected by a switch between the output tubes and transformers. (NOTE: Manual states the switch can only be used when amp is off).

In triode / ultra-linear mode the first 17W / 30W are pure Class A, switching to Class AB1 for a maximum RMS output of 30W / 60W.

These units came to us from a collector that had dozens of amps so I suspect they received little to no use.

They are working like new and ready to make someone happy. 

SkyFi Service Notes:
• These amplifiers received a fresh set of tubes from our stock.
• Output tubes are matched pairs of strong testing used Svetlana 6550.
• Driver and PI tubes are McIntosh and Sovtek branded 12AT7 and 12AU7.
• Both amplifiers tested to 60W and beyond before clipping with surprisingly good frequency response and channel balance.

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 - Speaker Cables - Good

Kimber Kable - Speaker Cables - Better

Kimber Kable - Bi-Wire Speaker Cables - Better (If Applicable)

Kimber Kable - Power Cords - Better

Kimber Kable - Power Cords - Best

Below is the information from the manual:
PROUDLY MADE IN THE USA

ULTRALINEAR MODE:
60 watts (into 2, 4, or 8 ohms)

THD+N (60 watts RMS, 20-20kHz):
<0.5%; @1kHz: <0.1%

Frequency Response:
20-20kHz, +0/-.25dB

Full Power Bandwidth:
5-75kHz, +0/-3dB

TRIODE:
30 watts (into 2, 4, or 8 ohms)

THD+N (30W RMS, 20-20kHz):
<0.8%; THD @1kHz: <0.2%

Frequency Response:
20Hz-20kHz, +0/-0.5dB

Full Power Bandwidth:
6-60kHz

GENERAL:
Input impedance:
300K ohms

Output impedance:
<0.70

Max.power before clipping:
70 watts

Dynamic headroom:
1.2dB

Signal-to-noise ratio (@60W):
Down better than 95dB

Input sensitivity:
1.2VRMS for 60W; (200mv for 1 watt; l.0V for 30 watts triode)

Gain:
+22.4dB (20 dB negative feedback)

Polarity:
Non-inverting

USA Tubes:
2 x 6550A
1 x 12AT7/6201
1 x 12AU7/5963

Case Dimensions - EACH:
9-1/2" W x 7-1/2" H x 11" D (12"D including binding posts)

Net Weight - EACH:
32 lbs.

Circuit Features:
- All-triode front end. Triode switchable output tubes.
- Massive custom-wound power/output transformers-exclusive custom designs by SV's Harry Klaus.
- Polypropelene signal caps. 1% metal film resistors. Hand-matched gain resistors. Mil-spec FR4 boards.. Shielded silver-Teflon wire between jack and board.
- Class AB1 operation-pure Class A to 30 watts (ultralinear); Class A to 17 watts (triode). Balancing trimmer on phase-splitter for ultralow distortion.
- Quality USA tubes: hand-matched, 48 hours burn-in. (May be internally reconfigured for EL34 or 6L6GC.)
- 2-ohm impedance load support for exotic speakers
- Visual bias adjust for each output tube. Instantly indicates tube status-shows when tube changes from Class A to AB, and eliminates need for matched pairs. LED indicator switch has center "off" position.
- "Soft Startup" for extended tube life. FET regulated power supply for front end tubes; regulated heaters.
- 2, 4, or 8 ohm selectable speaker impedance via four rear panel binding posts, "pyramid" configured for quick impedance changes via dual banana plugs.
- Ground lift switch for optimized signal-to-noise ratio plus IEC power socket with 14-guage power cord.
- Superb low volume level performance. Accurate musical colors, tonal timbres, and sound staging.

Cosmetic and Convenience Features:
- "Classic Chrome” plated steel chassis and bottom; additional internal supports for extra rigid platform.
- Stylized "Ultra-Vent ™" perforated cover-cage (included)
- Front panel tube bias LED status indicators
- Deluxe GOLD input signal jack and 30A 5-way binding posts

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.