Ok. You just had to ask. So, I spent a little time with PSPICE today so you can see the electrical response of the tone pot. The pickup is a Tele bridge. The conditions are as follows:
- Pickup inductance = 3.2H
- Pickup resistance = 7.4K
- Pickup interwinding capacitance = 160pF
- Volume pot = 500K (set at max CW)
- Tone Pot = 500K but 442K actual
- Tone cap = 0.05µF
- Cable = 20ft
- Amp input impedance = 1MEG
- Amp input capacitance = 100pF
The labels on the graph are
TONE KNOB SETTING (0 thru 10)/RESISTANCE. Remember it is a audio (non-linear) pot. The resistance values for the 0 through 10 positions are based on experimental data I collected on audio pots a few years ago.
Notice the resonance peak with no tone pot connected aka the no-load pot. You can now see how the TBX would give you everything between the max CCW and almost open.
I doubt some of you would experience the same no-load response as plotted because every amp input impedance is not as high as 1 meg. If the amp input impedance is more like 500K, that no-load response will be less pronounced. But, a Fender Twin is 1MEG input impedance.
Look at the curve for the 500K pot set on "8". Having a 250K pot (277K on the plot) is like a 500K pot turned down to "8".
Regarding the tone cap value, it matters most at a setting of "0". With the 0.05µF cap, the resonance is moved down to 300Hz. At other points on the dial, it is simply destroying the resonance at ~3.5kHz. If you used a smaller cap value, that resonance would be higher than 300Hz.