Sir Muldar . . . .

Never have run into that problem on that type of transformer at 10.7, usualy just the 455 units which are in series with the 10.7 in the circitry and dependence upon their great frequency disparity for the isolation of the units.
I have your other info additionally archived out at "The Mule Barn . . .in "Podunk Holler" but only grabbed the somewhat massive schematic info.

I would advise that initially. . .if not too late already . . .that you should assume that the rest of the IF strip is in alignment and
has never been touched. Then you tune into the strong signal of a FM station and place the scope probe to the insulation of the plate wiring from the limiter to the discriminator primary. (If a bare wire , a fold of vinyl tape upon it and scope probe clip on to the tape). WHY ? ? ? . . .I don't even like to see the potential detuning /loading effect of even a 10x probe on that circuitry. Use a
cranking up of the scopes vertical amps gain to make up for it.

THEN you just hope that your selected capacitive value for that L 12 and the primary is such that it is a wee bit more capacitance than was originally used. You will be wanting to initially have checked the scopes display to see that you have in order of 2/3 rds of the screen filled vertically. And with a strong signal the stage should be into full limiting and flat topping out of the IF signal.
What you need to do then is find a much weaker signal that is not flat topping , but that you can see its amplitude TRYING to go up and reach that saturated condition. Then you would want to make an initial assessment of that selected value of tuning cap present as the plate windings tuning component.

Hopefully on the insertion of a plastic / Delrin / nylon HEX diddling tool into the BOTTOM . . .A9 coil adjustment, you will find that a CCW movement of that slug will have resulted in an enhancement of the displayed amplitude of the 10.7 IF signal.
You just want to be sure that the eventual capacitive value ends up at resonance with the slug being slightly outwardly from center position within its coil. and I did say outwardly, as having it passing from center coil position and moving on INWARDS towards the outer discriminator secondary coil really fouls up alignment procedure and attainable results.

Another evaluation of needed capacitance value, as you might have mentioned, would be the initial shunting of that coil with a variable trimmer and use the same procedure , but never touching the coils original slug and trimming for resonance and then measuring the required value of cap needed.

If you find a cap that is a bit MORE than the desired value, I have corrected modern vintage El menco, Arco type of silver mica units by using a Dremel tool and a cut off wheel to the very tops and very bottoms to reduce the sizing a bit to result in diminishing the capacitance . When confirmed, a drop of lacquer, fingernail polish or epoxy reseals the unit.

Confirmation of secondary alignment using an off the air signal:


THEN you are ready to deal with a double edged sword in the aspect of the need of two like capacitor values.
To check that possibility you can check alignment by monitoring 6AL5 plate #5, hopefully with analog VTVM metering in its DC mode.

If you will then look down from that connection to [ A ] referencing, you can see that there is an isolative filter connection that is sending
correction voltage for the AFC circuit, that needs to be disabled by the grounding of terminal 1 of PC5. Tha then leavew you free to tune into a station without countractive AFC correction attempting to be made.

You then tune onto a station and note that if you are "RIGHT ON" in its tuning that the voltage output will be near 0 VDC.
Now here is the procedure you use to evaluate that secondary coils tuning, as you tune . .say to the left . . .the voltage should increase in a negative . .or. . .positive polarity value and then at some point come to a peak value and then start diminishiong
value with further tuning until it approaches the tuners capture range and pops off the station.

If you will then reverse tuning, to get the station contact re established, and approach that central tuning point where the DC voltage again should be near zero, with further tuning that voltage should be taking on the same effect as was being experienced before BUT with the polarity of the voltage being the opposite.

On using the main tuning condenser knob in tuning off from that station in both directions and if that secondary coils slug is properly positioned, the peak voltage read on both trials off of center tuning should have peaked at the same value.

Hypothetically on voltage value readings . . .if one tunes off to the right from 0 VDC and finds that the peak voltage reading is
+5 VDC, then in tuning back to 0 position and then tue to the left, its voltage should also peak at -5 VDC.
A finding of +4 VDC on a test along with a companion -6VDC reaing would signify an out of alignment placement of L 12 / top coil [A16 adjustment] slug. Likewise, you could have found a-4VDC or +6VDC or even a - 2 / + 8 VDC which would be a grossly mis alignmed placment of A16 coil slugs position.

You want them to be coincidental in values

Standing by . . . . . Reference schematic re tagged onto this post