As it turns out, somebody must have opened up the Wavetek 907A before, and it is missing a crucial part – the detector, for the leveling circuit! Checked out with the manual – there used to be a 6 dB pad (to get better SWR for the detector), and a positive-type tunnel diode detector (SMA input, SMA output). Nothing I have around here surplus.
Wait – there is a spare HP Schottky negative-type detector around in a drawer back home in Germany, and coincidence allowed to have it carried over to the US. This litte device as SMA input, SMC output, and with a little SMC to SMA adapter, at least a mechanical fit.
A little mod will is required to get this going, changing the polarity of the input amplifier. No big deal:
Next step – there are correction coefficients stored in the Wavetek (in ROM), to compensate for signal losses along the RF chain, and to keep the output calibrated. This will require some more thought, to be continued.