Hi,
Welcome to the world of open-reel tape, i am sure you will discover a new world of quality analogue sound recording and reproduction.
I acknowledge what Steve and Mark have pointed out about the virtues of machines of more professional design than a Revox, but there are several good things about Revoxes too.
First and foremost, what you have discovered already: many were bought as a prized possession by music lovers or audiophiles of in the old days and, since the primary media were LP records and FM broadcasts - and, later, CD's - many of these machines ended up being used very seldom. Since they were engineered to be very rugged, most domestic users' usage patterns hardly put a dent in them. Professional machines, however, were bought to be used and the best one can hope for is to find a properly maintained example - a barely used one would be a rare find.
Re. tape hiss: on Revoxes, the reference level set at a conservative 250nW/m, with plenty of "lead" to allow for the VU meters' ballistic characteristics. On my B77 Mk.II with IEC equalisation at 15ips and SM468 tape, same as used by the Tape Project, I have arrived at a setting of 355nW/m - that's 3dB above 250 - and _no_ ballistic compensation which adds another few dB (I don't recall offhand how much was recommended by Revox). I use this for making live recordings that are more likely to overload the machine than taping off LP's and have noticed no problems with distortion or saturation of the highs (but please note I record acoustic instruments). I have had similar good results also with copying LP's at both 15 and 7 1/2ips. The reason Revox used such a conservative setting was, I suppose, that they allowed for domestic tapes of much lower performance than the professional SM468, which was available back in the day but was largely unknown to home users, and they would also have allowed a margin for user error. So you are looking at, say, 6dB or more improvement in signal to noise ratio just from re-setting the reference level and VU meters to take advantage of pro-grade tape. The B77 electronics seem to have more than adequate headroom for this adjustment, I haven't had an A77 but I don't suppose its electronics would differ widely in available headroom from those of the B77.
About conversion to two-track format, all you need to do is change the heads and possibly a few components in the bias oscillator as well. I don't have an A77 manual. But I have done conversions on B77's and A700's, given the heads the conversion is easy. It depends if you want the two-track format. If the machine needs the heads replaced I would convert it to two track. But four track has its advantages too, especially when copying LP's where four track at 7 1/2ips is more than adequate quality for most LP's. Tape is expensive, four track gives you double the time but the heads have to be very carefully aligned to avoid "dead channel" crosstalk.
The other good thing is that the wearing parts are available and reasonably priced, and there are very few of them in each machine... it's a very simple transport.
By the way, when copying from LP's, monitor on headphones with your speakers silent. The absence of acoustic feedback to your turntable improves its performance to the extent that you may notice better performance from your copy tape when playing back from loudspeakers than when playing back from the turntable over loudspeakers. I've posted before in this forum about this in a thread about copying LP's. A Revox is good enough to show that difference even with high quality turntables, in my experience.
If you have any questions don't hesitate to post or PM me.
With best regards,