New build ... looking for some suggestions to make it even cooler

[Diverted]

Hi all,

I'm building a one-off amp in an old Setchell Carlson PA head. When I got it (ebay) power transformer was blown, half the wiring had been messed with by someone and it was a mess. So I scrapped the original circuitry and have built a new circuit in there. Went with a newer output transformer too as the original seemed very small.
My question is this: Check out the center right spot, where there is an empty hole for a potentiometer. If you were going to add one more feature to this amp, what would you do? I'm looking for suggestions. Thanks!

About the circuit
The amp's bones are a Fender 5E3. The normal channel has been re-voiced into an early Marshall per Rob Robinette's Lead channel mod.
Also:
Volume interaction has been removed, also per Robinette's mod.

Pre-phase inverted master volume installed.

I added a two-gang 1M pot to allow for tone control on both the stock and Marshall channel.

Power transformer I am using was putting out too little B+, about 60VDC too low with a 5Y3 rectifier. I don't have any GZ34s on hand so I swapped it out for a diode bridge. B+ is now at about 390.

I installed a three way feedback switch.

That's it for the most part. Bias resistor is 280; 250 called for in schematic was putting me just over 100 percent dissipation. Now it's running around 94 percent.

Like I said, I would love to come up with one more cool feature to add to this amp and fill that last hole on the face plate. Any suggestions for cool stuff would be great, thank you!

[shooter]

there is an empty hole for a potentiometer.

just add a pot to nowhere, hang a knob on the shaft and play

[sluckey]

I added a two-gang 1M pot to allow for tone control on both the stock and Marshall channel.

Use two single pots. All holes now plugged.