@ muvideo,
Thanks for the heads up on the high impedance mode. I missed that in scanning the manual.
Do your 7A22's have the awesome machined tuning capacitors like mine in this thread?. The manual I downloaded shows regular tuning caps in the manual. The jumpers that get unsoldered for the high impedance mode are shown in those pics also.
It's exactly the same:
By the way one of the mine was broken. One of the problems was
due to a deformed variable capacitor, pushed by the offset pot the
armatures were touching and it was shorted.
The other problem was a resistor cosmetically perfect but electrically
open, before I started checking the resistors I swapped all the
semiconductors and capacitor in that stage.
I was so amused by the fact that it's entirely passive design,
the schematic seem "simple" for the specs, but as everything the
devil is in the details.
In this case the high impedance mod precludes the use of the higher
input voltages, at least trows off the calibrated amplitude since the
attenuator expects to have there the 1Meg input resistor.
One could think to use a pair of switches or jumpers or reed relays
to connect and disconnect easily these jupers, but must be
careful with the eventual introduction of thermocouples with
the contacts.
Fabio.