I've got 3 early Tandberg reel to reels, Models 2TF (mono), 3B (stereo), 4 (stereo).

The 2TF has been my main focus. I have the owner's manual and schematics for it. So far, I've replaced the belt, pinch roller, and tubes (NOS '50s Telefunken!) It seems to work really well. My 6-piece band uses it all the time during rehearsals to track ideas mostly. We set up an old Turner 33D mic in the corner of the room, and let her rip. It's sounds okay, lo-fi, but not bad. But I've noticed that the bass tones tend to fuzz out. I'm wondering if the bias need to be adjusted. And if so, how do I go about doing that?

The 3B model, has been a lot of work with little results. I've replaced the belt and pinch roller in it also, hoping that I'll soon be able to make stereo recordings using the 2TF as a slave preamp. The 3B works just as it's supposed to. All the lights and meters work, rewind & fast forward are good. However, when I go to lock the lever into the play position, the reels begin to spin as it should up until the point that the lever locks into place... and then nothing! What gives?! I'm hoping it's something simple, like a belt issue maybe?

(The model 4 has been used for parts only.)

Any insight would be greatly appreciated. Thanks!