Level 1 -bare minimum to do

The bare minimum while the modification is to remove the loudness circuit and the low pass filter in tuner mode!

Please remove R49, C34 (R149, C134 on the other channel) to eliminate the totally unnecessary loudness.

If the tuner input is selected, then the negative feedback is stronger and amplification is lower and with this also the noise of the pre-pre amplifier is less (just take a look on the factory noise/signal rate). This is done with switching in R42 + C33 (R142, C133). Unfortunately C133 is realizing a low pass filter (FM radio is poor above of 12kHz so for that one it was fine, but not for hi-fi…) So due to lower, less noisy amplification, it is recommended to use the Tuner input, but please remove the C33 and C133.

For easy and reversible modification you can desolder one leg so they are then not part of the circuit. (solder one desoldered leg to the other leg…)

At any time you can solder it back (but why would you…). In the schematic section you can find drawing about component positions, so where you can find R50 or C34 or C33. But below is an after modification picture with desoldering one leg C33, C34 (C133, C134) and soldering it to the other leg.

Now your amp is already much better. If you agree then have to highlight this is just the begin to create a perfect amp, so please check the next levels.

Not improving th sound, but avoids killing your source devices: The not selected Tape or Tuner input is shorted to GND (Also the riaa) This was fine in the 60s to short weak tube signals with high impedance, but nowadays with high level/low impedance inputs this is not acceptable. So please remove this GND from the input selector switch or ensure you do not connect signal on the not selected input. More about this in level 2.

Note: AG9014 is very similar, but there you need to remove the C33, C133. Actually that design is even more dumb to be not symetrical in the negative feedback… (R142, R147, C133, oh gosh…)

Replace all electrolytics while not touching the Philips mustard, for details check components section. Replace R30, R130, 120K with caarbon composite – check also here the components seciton.