Ok... I desoldered the record/erase head and checked impedance:
--record head 165ohms... (right where you said it'd be!)
--erase head 7ohms... (whatcha think -- indicative of a partial short?)
Hooked the head back up and probed for a bias signal with the scope, but found nothing... As I mentioned, I'm a novice here, so let me recap in case of error: All I did was plug the probe into channel 1, set it for AC and the proper timing scale, and probe each head's "positive" lead (the other side of each head is tied to ground...) Saw nothing. Just to verify my scope, as it is largely a piece'o'shite, I connected it to a signal generator set to 100khz and did see a signal, although it was a PITA to stabilize the trace.
The above, assuming my methodology was correct, leads me to believe there is no bias signal. I was told the tubes are good, but I'm gonna run to a local electronics store today and test them just to be sure they're convincingly in spec (the store actually has an old public tube tester that supposedly works!)
Barring the possibility of bum tubes, I guess I need to probe around the oscillator circuit and find my missing bias signal? I'll study the schematic and see if I can figure whats goin on in there, but as always, any assistance is gratefully accepted!
In either case, thanks for getting me this far guys... learning every day with these little projects...
EDIT: forgot to mention... I did see audio signal across the record head, but not exactly what I expected. I fed the unit a 1Khz sine wave, then probed the record head lead expecting to see a 1k sine on the scope... What I saw instead was a distorted 1K signal -- looked like a 1Khz sine with an additional narrow peak riding atop the peak and trough of the wave... Not sure what to make of that, obviously something is getting injected into or distorting the signal...