The Maranzt 8B had a very nice OPT in it (It is a diferent animal than the pair in the original model-8). The amp as a whole is musical. As an historical collectors piece, the tube Marantz gear is classic and are collectors items (depending on condition). In the 1960s, Marantz arguably made the best sounding tube amps and preamp. The transformers were of a very high standard, but so were the transformers in the HK Citation II, McIntosh amps, Acrosound amps and a host of others.
I have owned, listened and repared/rebuilt a large number of classic amps. And I can share with you my opinion that the Audiogonzo pricing for classic Marantz gear is insane. Example, I owned a Marant 7 (there is no such thing as a Marantz 7C - straight out of the mouth of Saul Marantz). The Maranzt 7 is bested by MANY, MANY, MANY preamps made since. I think you can beat it with $600-$900 well directed dollars. Spending $2,000 on it for sonic reasons is silly. Spending more than that for sonic reasons is INSANE! It's main value is as a collectors item- PERIOD! Find one in mint condition and you have a collectors item! Find one in good condition and you have a piece of history! Same for the Marantz 8B. If you are into paying for a collectors piece, then you will be parting with a lot of money. NOW REGARDING PARTS. If you own one of these. Pull out the electrolytic caps and have them tested. If they are good... put them back in or replace them with good parts of the same type. Test the coupling caps for electrical leakage and only replace those that have gone bad (while this is important in general, it is VERY important in a power amp, especially between the driver and output tubes). DO NOT replace the carbon comp reistors unless they are cracked, open or drifted off of spec. And for the love of Mike, don't replace them with modern metal film resistors. You will not only change the sound (which you may not like) of the historical collectors piece, you will ruin it's REAL re-sale value. I repeat, these things cost a bunch of money not because they sound better than everything else (most well made modern stuff sounds as good or better) but because they are historical landmarks of audio - providing you don't slap a bunch of modern parts in them. You don't buy an original 1937 Cord and replace everything in it with modern parts... unless you wish to kill its true value.
I own and use Tamura, Tango and Nature Sound Transformers in amps of my own design and build. They are truly very good transformers. Tamura makes some average stuff and they make some great stuff. I can't comment on the quality of the Air-tight trannies, but if they are made to the level of my Tamura Permalloy tannies, then they are indeed, very good.
BTW, In a tube amp... obviously the circuit design matters, but after that... transformers (and good tubes) will make more of a difference than caps and resistors. When looking for a good amp (obviously how they sound is important) choose an amp with a solid circuit design and great transfomers. The transformers are the most expensive parts. You can always fool around with caps and resistors after the fact.But if you own an old Marantz or McIntosh amp, please, don't change the caps and resistors to modern parts - you will change the sound and kill the true value of the amps.