The Manley Reference 150 Watt Monoblocks were built at the old VTL factory back before the Manley/VTL split-up in 1993. They put out around 150 watts depending on which output tubes were in there and where you declared maximum to live, at 1.5% or 3% THD at 1KHz.

They were 4-output tube designs usually strapped in Ultra-Linear operating mode, although some had triode-tetrode switches on the faceplate (triode was always "up"). The 150's used the GE6550 output tubes before 1990 and the KT90's after that. The Input tube was always the 12AT7A or 6201. Some early models might have used the 12BH7A for driver tube although most of the actual production models probably used 6350 driver tubes. (Sorry my memory is failing me. Just read the number printed on the tube as the two types are not interchangeable without circuit board modification.) 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!

These amplifiers had adjustable FEEDBACK and SLOPE controls. They both are 3-position switches. The FEEDBACK control adjusts the amount of negative feedback. As I recall these were 1.5dB steps. For more info about negative feedback, go read this. The SLOPE control adjusts the feedback capacitor changing where the super-sonic roll-off of the amplifier takes place. The best way to use these controls is just to listen to each setting and pick which one you like best.

Manley 150's had a sheet-metal "deluxe" chassis and sometimes also stainless-steel covers. Bias readout tipjacks are located on the faceplate where it says "Read Bias" and the four position switch below those tipjacks selects which tube you are reading while the bias adjustment pots are located in a row in front of the two big grey B+ caps on the top deck. Additionally there are driver balance measurement points and corresponding trimpot to set the AC balance ocated near the driver tube, maybe inside the amp. These 150's were quite similar to the Manley Compact 160's of the time circuit-wise but have much larger filter caps and B+ supply. Both the output and power transformers were manufactured by Mercury Magnetics. The output tranny was factory set for an optimal 5 Ohm speaker load but it can be reconfigured by soldering the output taps in different series or parallel configurations. It was was on the better sounding output transformers of the time, same as found in the older Reference 100/200 model.

If it doesn't say "MAN1505###" on the serial badge then you don't have a Manley Reference 150.

This particular amplifier pictured here had an XLR connector and volume control fitted. Not all of them did. The XLR was paralleled to the RCA and was always unbalanced as the input circuit is unbalanced in this model. I cannot recall any balancing transformers being fitted to these.

This model ceased production in 1993 and was never manufactured at the new Manley Labs factory. For biasing info, read the owner's manual. You can safely follow the biasing instructions found in the Manley 350W owner's manual. We still do perform warranty service on these old amps, so if you need help with yours, please get in touch.

There was never an owner's manual for this model. Those were the days.

The pictures on this page were lifted from an eBay auction I spotted. These amps rarely come in for service so we don't have a picture that we have taken. There were maybe around 25 to 30 pair of these built. This picture shows the cage they usually came with (no, we do not have any more of these cages):


This unit was QC'd by Manuel Monroy on 2-25-1989:




  • Output 4 x 6550 or 4 x KT90
  • Driver 12BH7A or 6350
  • Input l x 12AT7WA
  • Input sensitivity: 0.750V 
  • Input Impedance: 100 kOhm
  • Output load impedance: Factory set for 5 Ohms nominal
  • RCA Unbalanced input (sometimes had paralleled XLR connector)
  • Front Panel bias measurement with Top Deck Bias adjust
  • Mercury Magnetics power & output transformers
  • S/N ratio: better than -90 dB
  • Power consumption: yes, definitely
  • Large filter / reservoir capacitors
  • Max output power: 150 watts
  • 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: 
  • Dimensions: slightly bigger than a bread box
  • Shipping weight: around 60 lbs. Sorry I haven't picked one up in awhile. They do not come in for service very often.

Specifications subject to change because they just might.