MUSICAL FIDELITY A1, B1, MA50
Musical Fidelity A1, B1, repair - £159 (or repair + full recap with higher quality long life electrolytic capacitors - £204)
Musical Fidelity MA50, MA65 - £129, ( or repair + full recap as above - £169 per amp )
The A1 has always had a strong following with a distinctive warm tone that sounds very different from almost anything else in it's price range (one of the main reasons I suspect being at the end of this paragraph). Despite it's pleasant sound the build construction is quite rudimentary by the standards of today and has nothing in common with the excellent Musical Fidelity equipment produced in recent years which is in a very different league. In conjunction with variable component quality often pushed close to their limits it has never made for a particularly reliable ownership experience but the unique sound for it's price range almost forgives it's frequent affinity for the workshop bench. Despite the class 'A' label and the ultra pure sound folklore that circulates amongst the audiophile community these are not quite as 'pure' as their reputation might lead you to expect when put through their paces on an audio distortion analyser and a Cyrus One/Two will easily surpass distortion performance in comparison. It is this distortion however gently 'coloring' the sound which results in it's characteristic warmth (much in the same way that a studio would use an Aphex aural exciter to liven up bland recordings!)
These are generally accepted by most to be only biased partly into Class A (i.e low volume levels) with the entire top lid acting as a heatsink it does run astonishingly hot and anyone with an ounce of engineering common sense may find the temperatures attained quite surprising! With internal temperatures in excess of 65C adjacent the heatsink do not expect the usual 30 odd year lifespan from electrolytic capacitors (or many other components for that matter!). Almost all A1's seen here in the workshop have at least 25% of their electrolytic capacitors beginning to suffer from high ESR and falling capacitance (mainly budget 85C rated varieties although occasionally you see a few decent Elna's and Rubycons mixed in). The PCB suffers from localised hotspots around certain components and thus dark brown burnt patches are normal. In fact the internal appearance is often more akin to a home constructed kit but don't let that put you off as if you can live with the 20W output they really are a worthwhile buy for a cash strapped audiophile. As the very early models were simply a sealed box with no ventilation whatsoever the later ones with the vented side panels are a much better used buy. Those with a painted lid/heatsink will shed their paint rather easily (tip - use satin black VHT engine/caliper enamel to refurbish and you'll enjoy a far more robust coating than original) Also expect noisy volume controls and intermittent input selectors along with various parts of the case often never quite fitting together properly and you won't be dissappointed.
The MA50 mono power amplifier is an A1 minus the preamplifier circuitry, a higher 36V supply and the outputs of left and right channels simply paralleled at the loudspeaker sockets. With 50W output it suffers the same heat related degradation as the A1 and well used examples benefit from a new set of electrolytic capacitors now that all are over two decades old.
Later examples appear to actually use a B200 PCB using a MOSFET output with the B200 markings on the PCB underside hidden with a large sticker.
In summary if you hate things failing then an A1 is probably not for you. If you can tolerate the potential for unreliability however then they will reward you with a sound like no other for a fairly modest price.