Manley designer ref. 300 series amplifiers

The Manley Reference 350 watt monoblocks were built at the old VTL factory back before the Manley-VTL split that took place in 1993. They were, at the time, Manley’s second-to-largest models in the Designer’s Reference Series. As 8-output tube designs, the 350’s were usually ultra-linear configured (although some units were fitted with triode-tetrode switching) and used either GE 6550A’s before 1990 or KT90’s after 1990. The Input tube was always the 12AT7A or 6201. Some early models used the 12BH7A for driver tube although most of the actual production models used 6350 driver tubes. Those two tube types have the grids and cathodes swapped on the pinout so make a big note that the 6350 and the 12BH7A are NOT interchangeable without reworking the circuit board. Flanking the driver tube there were two additional readout test points and an additional trimpot for the driver AC balance adjust.

Manley 350’s have a sheet-metal chassis and stainless-steel covers. Cool features of these amplifiers include the adjustable “slope” and “feedback” controls that allow the user to select different feedback capacitive and resistive values respectively. Changing the capacitor in the feedback loop changes where the high frequency rolloff of the amplifier starts. Bigger capacitor will make the amplifier’s super-sonic roll off earlier. Also handy is the front panel mounted bias readout tipjacks and tube readout selector even though one still has to address the top deck of the amplifier to make the actual bias adjustments. Many of the later Manley 350’s had MIT-Multicaps. And some of them even had TRIODE / TETRODE switches.

Both models ceased production in 1993 and were never manufactured at the new Manley Labs factory.

Manley 350 Watt Monoblocks

ALL-TUBE monoblock design
6350 driver stage
12AT7WA input tube
Output tubes: 8 x 6550 (before 1990) or KT90 (1990-1993)
RCA UNBALANCED input
Mercury Magnetics power & output transformers
Power output:
380 W 3%T.H.D. feedback MAXIMUM
376 W 3%T.H.D. feedback STANDARD
360 W 3%T.H.D. feedback MINIMUM
Factory set for 5 ohms nominal
Front panel bias measurement and adjust
Variable Feedback 3-position switch
Variable SLOPE: 20 KHz, (Ref. to 0dB @ 1K)
+1 dB slope MINIMUM
+0.97 dB slope STANDARD
+0.88 dB slope MAXIMUM
Large filter / reservoir capacitors
Input sensitivity for full power, feedback set at
MAX 1.8 Vrms
STANDARD 1.44 Vrms
MIN 1.2 Vrms
Input Impedance: 82 Kohm
S/N Ratio: better than -90 dB
Power Consumption: enough to occasionally trip circuit breakers on turn-on
300 W Quiescent
900 W Full Power
Factory set for 100V, 120V or 220-240VAC operation for original destination country’s mains voltage.
Operating Mains Voltage changeable with power transformer re-wiring and fuse value change.
Mains Voltage Frequency: 50~ 60Hz
Mains fuse 120v operation use 10A SLO-BLO; 220v use 5A SLO-BLO
B+ fuse use 1.5A SLO-BLO
Shipping weight: about 80 lbs.

pdf manual: www.manleylabs.com/PDF/HIFI_Manuals/Hi-Fi/manley350.pdf

“I have used these valve Manley amps to drive my Dynaudio M2 monitors and have not been disappointed. The sound actually improves and opens up as the amps warm up, giving you a real sense of valve presence. Inviting, warm and always bringing a smile, the Manleys are all that they should be. Don’t try lifting them though – they weigh a ton! My needs these days are more towards smaller near-fields and, as with huge monitoring in general, they are proving something of a luxury for me. They were used a lot during the 5.1 mixing of ‘subHuman’ where I could really test the full frequency range and power of that album. Recently refurbished, with some calibration, valve testing & replacement by John Earls, they couldn’t be in a better state.”