An AF lens should meter on a D70 or a D70.  It's the older manual
focus lenses (the AI and AIS lenses) that will not meter on the
amateur bodies.  I used such old lenses with my Fuji S2 a lot; they
don't meter (and of course don't autofocus, either; they were never AF
lenses), but they're still quite usable for me (but I've worked with
cameras without built-in meters before; I'm used to keeping an eye on
the light and adjusting, and making quick checks of the histogram
makes it very easy to keep the exposure on track).

Does that lens have an aperture ring?  If so, make sure it's set to
minimum aperture (largest number, probably f/16 or f/22).  There's
probably some kind of lock to keep it there, too.  This is necessary
to enable aperture control from the camera body.  I'm not certain this
is the right answer; I don't know if getting that wrong on those
models results in that error (obviously I don't have those exact
models to play with).

I've used that lens on a Fuji S2 and I believe on the D200
successfully (no metering on the S2).  So it should be okay.  I've got
Tokina, Tamron, and Sigma AF lenses, as well as Nikon MF and AF lenses
I use.  I've never had a compatibility issue with Nikon cameras and
lenses (though some exist, the old 21mm version that needs mirror
lockup, for example, it sticks in too far to be used with the mirror
down).

If I put an older AI lens on my D70 I also get an "F" error.  That's because
the camera cannot read the aperture of your lens or couple to the meter.
The aperture will have to be set manually using the aperture ring on the
lens, and the lens will have to be focused manually.  The camera should show
focus lock, however, as a green dot, even though you have to do it manually.
Shutter speed is controlled by the wheel on the camera body.  If the camera
is on and set to M you should be able to take a photo.  I have several older
AI non AF lenses that work just fine in M mode.

What surprises me is that most auto focus 35mm lenses will couple to the
camera and work automatically.

Consider a Canon.  Works fine in stop-down mode with older manual-focus
Nikon lenses with a suitable adapter.

You can use an AI or AI-S lens, but it will not autofocus, of course.
Also, the autofocus light will not work with a reflex lens. The lens
must also have a maximum aperture of at least 5.6 for the focus
confirmation light, so an old, slow reflex lens is just not going to be
very useful. Aperture priority (A), Shutter priority (S), Program (P),
and Auto (A) modes are unavailable. You will have to set aperture
manually. You will also have to turn off the "Auto" ISO mode in the
menu and turn the M/AF switch to M. My guess is that you still had
Auto ISO set in the camera and possibly also had the M/AF switch wrong.
With an AI-P lens you have to have a maximum aperture of 5.6 for the
focus confirmation to work in the viewfinder and it will not autofocus.
Also, you cannot use 3D matrix metering, so the meter will not use
distance in its calculation.

Your Tamron should work fine, but I am not sure I would trust the
doubler.