MFA, MC Reference, Original Prototype - Mono Blocks I am the original owner of the Prototype Mono Blocks MFA built to be the paring to the MC Reference Preamp. I have held them since purchased in 1991. Those of you who know about the MC reference preamp know what a quality piece gear it was. You also know this was MFA's all-out assault, cost no object preamp that set the very pinnacle of what tube preamp technology could be. These mono's were slated to be the pairing to that preamp. There were only 10 preamps ever built and these amplifiers are the ONLY pair in existence.
Description: The amps are completely hand built, 100% point to point wired with custom hand wound transformers manufactured and tested to be identical in specs and measurement. The amps are hard wired in triode so there is no Ultra-linear or Pentode switchability. There are no meters or extra components like one would find on a 120 or 200. The output tubes and AC balance must be biased using a separate multi meter and there are plugs for this on amp. All the non-signal equipment that would normally be present on the 120 or 200 has been deemed not necessary and eliminated. The only two switches on each mono block are power and a negative feedback elimination circuit. The Negative feedback circuit was a test switch of which would likely be eliminated on a production run. The regulation is so good, the negative feedback loop has approximately 8db when switched on. (Normal for a stock MFA120 would be around 20db or more and has shown to knock down the sound stage.) You can also run them without any feedback for a monstrous sound stage but the specs fall off a bit. One cannot do any of this on a stock MFA 120 or 200. All tubes have been upgraded to the Mil-Spec 8 and 9 pin 5687 and octal 5691. Output tubes are real (Not fake) OEM GE 6550's but you can run kt88"s or kt90's or Gold Aero's or 300B’s if you can find some NOS. There are several capacitors, resistors and diodes, including the power bridge that were upgraded over a 120 or 200, too much to list and most forgotten due to time.
I have held them now for more than 26 years, the last 15 sitting in boxes with occasional use to see how other gear stacks up. They are impeccably well preserved, stored indoors, no smoke or pets. Why am I selling? My tastes have evolved and I simply don't use them enough to warrant holding them, besides, it's time for the next Audiophile to enjoy them. Absolutely-positively no disappointments. They really are special amps, nostalgia and sound quality.
Disclosure and condition: The only unfortunate part about these amps is that they are prototypes that were built on prototype chassis. Hence they are not the most attractive amps and have mounting stamp-outs and drillings that were never used. Some outright rough cuts too. I suspect that is what makes them special. For that I rate them 8 of 10 but they are very clean for older gear. They also have adjustable AC bias and output jacks for bi-amping. The speaker cable binding posts are not traditional posts but are a panel type, non magnetic mounts that accommodate 4 & 8 ohm loads and are era correct for this Amp.
For more information, please write me. I have documented the development of the circuit as much as possible given the product never saw formal production and I will be more than happy to disclose all I know.
Payment: PayPal plus 3%. It's my preference to take a check or wire transfer. email me to work it out but let’s save each other the PP fees.
Shipping: There never were boxes or manuals for the amps and if you are not local they will require special boxes and/or creates with appropriate packaging to be made from scratch. I will cover the creating expense, you will need to cover the shipping expense.
Thanks for looking. firstname.lastname@example.org 408-489-1414