Install a Post Phase Inverter “Tone Cut” Control
If you regularly run the amp at heavier distortion level,
a post phase inverter tone control is very useful for
taming the high end response of the amp. This tone
control is identical to what can be found in the vintage
Vox AC30 as well as many boutique amps. I
recommend removing the second speaker output jack
to use as the chassis hole for this control.
Step 1
– Install a 250K linear taper potentiometer into
the chassis
Step 2
– Solder a 2 or 3 position terminal strip to the
back of the pot (photo 11e).
Step 3
– Solder a .0047ufd / 630V cap between
terminal 1 of the pot and one of the outside lugs of the
terminal strip (not the middle grounding terminal).
Step 4
- Install two 20AWG wires 7” long between
terminal 2 (the wiper) of the pot and the solder terminal end of the .0047 / 630V capacitor.
Step 5
– Twist these two wires together and run them neatly to turrets T48 and T38. Cut to
length, strip and tin the end of these wires and then solder them around these two turrets.
There should be wire routing holes located near these turrets to facilitate neatly routing these
wires under the board if so desired.
Install a Choke in the Power Supply
By installing a choke in the power
supply, the dynamics of the amp will be
quicker and the low end will hold
together better. The amp will have
slightly more power output and any
hum residual will decrease even further.
The inexpensive choke as used in the
Fender Deluxe Reverb is a perfect
choice for this application.
Step 1
– Attach the choke to the inside
of the chassis near the power transformer with #6 screws and nuts (photo 11f). You will have
to drill holes in the chassis for this.
Step 2
– Twist the two black wires of the choke loosely together and run them neatly over to
the can filter cap.
Step 3
– Remove the 2.2K / 3W resistor from across the terminals of the can cap. In place of
the 2.2K / 3W resistor, install the two black wires of the choke (photo 11g).
Install a Post Phase Inverter Master Volume (PPIMV)
There are many master volume control options, however this version is my personal favorite.
It is a bit complicated to wire but the sound is very good.
TubeDepot.com 57
1
Photo 11e
Photo 11f
Photo 11g
2
3
These directions refer to mounting the MV control in place of one of the vibrato input jacks.
Other options are in place of one of the speaker jacks or drilling a dedicated hole.
MOD
