Yes indeed based on how the cap is built. There is an inside and outside foil and many brands mark the caps so you are aware. From the Aiken amplifier site;
The proper way to connect the outside foil is to the low impedance side of the circuit, which, in the case of coupling caps, will normally be the plate of the previous stage. If it is a bypass cap to ground, connect the outside foil to the grounded side. If it is a bypass cap from a signal to B+, connect the outside foil to B+. The outside foil will act as a shield against electric field coupling into the capacitor, so you want it to have the lowest impedance return path to ground.
For AC signals, the power supply rail is effectively at ground potential, just as the ground rail is. This is why it makes a good point to use as a shield ground. This concept is sometimes difficult to understand, but if you think about how a capacitor works, it will become clear. A capacitor has a capacitive reactance that calculated as follows:
Xc = 1/(2*Pi*f*C)
where: Xc is the capacitive reactance
f = the frequency of the signal being passed through the capacitor
C = the capacitance of the capacitor.
As you can see from the above equation, the frequency term is in the denominator, so as the frequency increases, the capacitive reactance decreases. Since reactance is effectively a measure of the "AC resistance" of the capacitor, the capacitor will exhibit a very low resistance at higher frequencies, while looking like an open circuit for DC and frequencies low enough to make the capacitive reactance significant. This means that the large electrolytic bypass capacitors in the power supply are effectively "short circuits" to AC signals above a certain very low frequency. For all practical shielding purposes, connecting the outer foil to the power supply rail is just as good as connecting it to ground. As a side note, electrolytic capacitors have an internal resistance that tends to rise with frequency, which can make the capacitor less than ideal as a bypass at higher frequencies. For this reason, it is sometimes a good idea to bypass electrolytic capacitors with a smaller value foil or other type capacitor.
I have seen where a well-known guitar amplifier "guru" said to connect the banded end to the grid of the next stage because it is at ground potential. This is completely wrong, because the grid circuit is a very high impedance point in the circuit. The grid of the tube itself is very high impedance, and it is usually shunted by a high resistance of 220K to 1Meg, and also usually has a large series resistance as an interstage attenuator as well. Because of this, it would make a very poor choice for electrostatic shielding. The plate, on the other hand, has an impedance equal to the internal plate resistance of the tube in parallel with the plate resistor (assuming the cathode is bypassed), which for a typical 12AX7 is around 38K total. If the cathode resistor is unbypassed, the output impedance is a bit higher, around 68K or so, depending on the value of the cathode resistor, but still well below the input impedance of the next stage. Tubes with lower internal plate resistances, such as the 12AT7, will have even lower output impedances.
The proper way to connect the outside foil is to the low impedance side of the circuit, which, in the case of coupling caps, will normally be the plate of the previous stage. If it is a bypass cap to ground, connect the outside foil to the grounded side. If it is a bypass cap from a signal to B+, connect the outside foil to B+. The outside foil will act as a shield against electric field coupling into the capacitor, so you want it to have the lowest impedance return path to ground.
For AC signals, the power supply rail is effectively at ground potential, just as the ground rail is. This is why it makes a good point to use as a shield ground. This concept is sometimes difficult to understand, but if you think about how a capacitor works, it will become clear. A capacitor has a capacitive reactance that calculated as follows:
Xc = 1/(2*Pi*f*C)
where: Xc is the capacitive reactance
f = the frequency of the signal being passed through the capacitor
C = the capacitance of the capacitor.
As you can see from the above equation, the frequency term is in the denominator, so as the frequency increases, the capacitive reactance decreases. Since reactance is effectively a measure of the "AC resistance" of the capacitor, the capacitor will exhibit a very low resistance at higher frequencies, while looking like an open circuit for DC and frequencies low enough to make the capacitive reactance significant. This means that the large electrolytic bypass capacitors in the power supply are effectively "short circuits" to AC signals above a certain very low frequency. For all practical shielding purposes, connecting the outer foil to the power supply rail is just as good as connecting it to ground. As a side note, electrolytic capacitors have an internal resistance that tends to rise with frequency, which can make the capacitor less than ideal as a bypass at higher frequencies. For this reason, it is sometimes a good idea to bypass electrolytic capacitors with a smaller value foil or other type capacitor.
I have seen where a well-known guitar amplifier "guru" said to connect the banded end to the grid of the next stage because it is at ground potential. This is completely wrong, because the grid circuit is a very high impedance point in the circuit. The grid of the tube itself is very high impedance, and it is usually shunted by a high resistance of 220K to 1Meg, and also usually has a large series resistance as an interstage attenuator as well. Because of this, it would make a very poor choice for electrostatic shielding. The plate, on the other hand, has an impedance equal to the internal plate resistance of the tube in parallel with the plate resistor (assuming the cathode is bypassed), which for a typical 12AX7 is around 38K total. If the cathode resistor is unbypassed, the output impedance is a bit higher, around 68K or so, depending on the value of the cathode resistor, but still well below the input impedance of the next stage. Tubes with lower internal plate resistances, such as the 12AT7, will have even lower output impedances.